A piston engine. In the '70's, Mazda commercials compared the rotary to the piston engine by explaining that pistons and valves are inefficiently "boinging" up and down, while the rotor just goes "hummmmm", efficiently around and around.
There are lots of reasons, but the main one is that traditional boinger displacement is a half truth. Advertised boinger displacement counts all cylinders, even though only half of them are capable of doing work during a single standard work cycle, one engine revolution. As a consequence, a "2292 cc" piston engine is not functionally twice as big as an 1146 cc 12A Mazda rotary.
That's right! The following comparison of a Pinto engine to the 12A explains why.
A 12A feeds two power cycles into the eccentric shaft for each revolution it makes. Each rotor face displaces a volume of 35.0 cubic inches, which is 573 cc. Therefore, 70.0 cubic inches or 1146 cc's worth of power are delivered to the output shaft for each revolution that shaft makes.
The most common Pinto engine, a contemporary of the early 12A, was a 4-cycle, 4 cylinder, having four pistons that each displace 35.0 cubic inches or 573 cc. Exactly two of these four cylinders deliver power to the output shaft in one revolution, which just happens to be exactly the same 70 cubic inch or 1146 cc amount as a 12A is doing in the same amount of time.
A key point here is the element of time. We measure engine size with reference to two things: time, and output shaft movement, revolutions per minute, or RPM. To make some other form of spark ignition internal combustion power plant with distinct intake, compression, power, and exhaust phases as does the 4-cycle piston engine comparable to it, equal parameters have to be given equal consideration. Therefore, since the 12A delivers two power cycles of 35 cubic inches each per output shaft revolution, it is exactly equivalent in this regard to the 4-cycle 4 cylinder Pinto engine that does the same thing.
Another way to look at equivalence is to quit trying to convert the rotary to 4-cycle piston equivalence, instead converting the boingers to rotary equivalence. The number of working chambers or pistons is irrelevant. Simply compare displaced volume converted into combusted mixture per output shaft revolution. The 12A is 35.0 cubic inches times two, or 70.0. The early Pinto just happens to be 35.0 times two as well, making it a 12A equivalent. The 13B is 40.0 times two. Later Pintos just happen to be 40.0 times two as well, making it equivalent to a 13B. An old 2.6 liter six cylinder Datsun 260Z happens to have 26.666 times three, or 80.0 total, same as a 13B. Since 4-cycle boinger pistons only put power to the output shaft every other revolution, they should be rated at half the displacement they claim to have!
There are noteworthy differences. The rotary makes excellent HP because it easily lends itself well to operation at higher shaft speeds (RPM) that get more power pulses into the output shaft per unit of time. The piston engine delivers it's power in shorter bursts of a nominal 180 degrees of output shaft revolution. The 12A nominally uses 270 degrees to deliver each of it's power "strokes".
A 12A engine is tuned to operate at a higher RPM level than the Pinto, so its maximum HP is higher. However, when both engines are operated at 5000 RPM, the small difference in HP is more a function of each's individual tuning than the differences in basic design. And, it is this correspondence that helps confirm the logic used above to compare the 12A engine to the Pinto 2.3L, and why it is the method of choice in racing classes in which rotaries are permitted to race against boingers and yet be competitive without being dominant. Doing it any differently upsets the competitive balance.
Equivalences other than 2 to 1 used by race santioning bodies are simply an attempt to equalize results instead of using what works for the boingers, capacity for them being the sole primary criteria of equivalence. The use of a factor of 2.6 recognizes that the rotaries operate at higher RPM's than the boingers in the same classes. If we convert the Pinto 2.3L into rotary equivalence, cutting the displacement in half from 140 to 70, the 2.6 becomes 1.3 to get the same equivalence. A maximum operating speed, redline if you will, of 7000 in racing trim for the Pinto, or any 2.3L stock based four for that matter, is probably realistic. Apply the 1.3 factor to the 7000 redline and what do you suppose we find? A 9100 RPM rotary redline in racing trim comparable for that class. Pretty slick of those rule makers, huh? They know more RPM can make more power.
Most simply put, the Renesis engine, the heart of the RX-8, makes more power, and emits less pollution, as a result of technological evolution. This evolution boils down to one fundamental difference between the Renesis and preceding generations, and several tuning elements that follow as a consequence of the fundamental difference.
Older generations, much like boingers, include significant overlap between the end of the exhaust cycle and the beginning of the intake cycle. During the overlap period, high exhaust pressure forces some exhaust gases through the chamber space between exhaust port and intake port into the intake charge, reducing overall intake efficiency. In supercharged versions of prior generations, intake pressure is at times higher than exhaust pressure, allowing some of the intake charge to be forced through the connecting chamber space into the exhaust. This overlap period is responsible for reduced operating efficiency at low engine speeds, while tuning compromises made to minimize the effect of this characteristic reduce efficiency at higher engine speeds.
In stark contrast, the Renesis port configuration includes no such overlap period. In fact, there is a dwell period between the end of the exhaust event and the start of the intake event, something totally without parallel in any production boinger. The only exhaust available to dilute the intake charge is the residue present in the chamber volume, primarily in the depression in the rotor face. Likewise, since there is no overlap, none of the intake charge is ever delivered directly into the exhaust. Result: greatly improved overall efficiency.
No other manufacturer has won such a long string of consecutive championships. The 1979 season was almost the first in the string. Mazda had 199 points to 1st place Datsun's 211. The 1979 season opened with the RX-7 IMSA debut at the 24 Hours of Daytona, where RX-7s finished first and second in GTU. Also in 1979, Mazda won the Champion Spark Plug Challenge with 246 points to 2nd place AMC with 218 and Datsun with 100. Mazda RX-3 drivers took took the first three places in the series' drivers' points race. Results like those take two basic things: 1- Power, to be first, and 2- Reliability, to stay first.
Like any other engine, the cooling and oil systems must be kept up to snuff to maximize reliability. If you let a boinger overheat, a typical result is a blown head gasket. The nature of rotary overheating is that a "head gasket" type failure requires a total overhaul to repair. If you can avoid such neglect, you can expect extraordinary service.
No. While it is true that the RX-7 was discontinued, its production run lasted 23 years. The RX-8 now provides a home for Mazda's newest production rotary, the first generation Renesis, and Mazda continues development efforts along several threads, including alternative fuels, such as the dual hydrogen/gasoline fueled second generation Renesis 16X. Rotary engines are produced by other companies for use in marine applications, model and experimental aircraft, and various stationary power applications. See links to car stuff for links to a few. Conversion packages are also available for using Mazda rotaries to power light aircraft.
The numbers represent metric displacement. Power is generated from one face of each rotor per shaft revolution. 10 is the result of two 491 cc rotor chambers, 982 cc total, which rounds to 1.0 litres. 12 is the result of two 573 cc rotor chambers, 1146 cc total, which incorrectly rounds to 1.2 litres. 13 is the result of two 654 cc rotor chambers, 1308 cc total, which rounds to 1.3 litres. 16 is the result of two 800cc rotor chambers, 1.6 litres. 20 is the result of three 654 cc rotor chambers, 1962 cc total, which rounds to 2.0 litres.
The letters "A" & "B" represent the combination of two basic production engine configuration parameters, "eccentricity" and "generating radius". The "A" is applied to the first (A), and only, combination of the two specifications actually deployed in a regular production engine of nominal 0.60 litre displacement per rotor, the 12A. The "A" was also applied to the first (A), and not only, combination of the two specifications actually deployed in a regular production engine of nominal 0.65 litre displacement per rotor, the low production 13A. Mazda later determined greater economy could be achieved by using the 12A's combination of eccentricity and generating radius in conjuction with a wider rotor, thus giving birth to the second (B) regular production rotary of nominal 0.65 litre displacement per rotor, the 13B. If Mazda were to create new two rotor engines of 0.60 and/or 0.65 litre displacement per rotor using some different combination of generating radius and eccentricity, application of the same logic previously applied by Mazda in naming its rotaries would give birth to a 12B and/or a 13C.
|10A, 12A, 13B, 20B||15 mm||104 mm|
|13A||17.5 mm||119 mm|
Interchange shows which engines were used in which cars.
Why, to sell you more spark plugs and spark plug wires at each tune-up, of course!
Actually the upper pair of plugs, called the "trailing", reduce emissions considerably, and improve power by a small amount as well, compared to using only the leading plugs. This happens because of the polymorphic nature of the rotary combustion chamber, which changes both in shape and position as the combustion process takes place.
So, why not just the upper plugs instead of four?
The spark needs access to the combustion mixture to light it effectively, but it can't actually be in the combustion chamber like in boingers, because the apex seals would either break off the tips of the plugs, or destroy themselves on the plugs.
So, the spark is located outside the combustion chamber in a recess. Whenever an apex seal is over one of these recesses, gas can leak through the recess from one chamber to the adjacent chamber, reducing efficiency.
At the location of the trailing plug recess, the gas pressure on either side of the apex seal is quite different, so the amount of potential leakage is large, and therefore the recess must be small to minimize leakage. Unfortunately, combustion instability at low load is a problem if the only plugs used are at the trailing location.
Conversely, at the location of the leading plug recess, gas pressure on either side of the apex seal is approximately the same, so the amount of leakage potential is small, and therefore the recess can be much larger, which improves idle combustion stability. However, the location of the leading plugs is not ideal for maximum efficiency overall. Power is reduced by about 2% and unwanted emissions increased if only the leading plug location is used.
Using four plugs allows idle quality to be maximized via the leading, and overall efficiency to be maximized via the trailing. In addition, the leading and trailing plugs are timed differently in order to improve overall efficiency further.
Some of Mazda's racing engines use three plugs per rotor to improve efficiency and reliability slightly further.
The rotors have no direct contact with the "cooling system", insulated well from the rotor and side housings, where the cooling passages connected to the radiator are situated. The eccentric shaft has oil jets that spray oil onto the back sides of the rotors to provide the required cooling. Without the oil cooler, the oil would get too hot and cease to lubricate.
On a related note, I've never seen dowel o-ring leaks on a 13B or pre-'83 12A. When rebuilding a 12A that has had dowel o-ring leakage, the old o-rings are very hard & will break if you try to bend them. This indicates that the '83-85 12A's get the oil hotter. In turn, this indicates that oil cooling in these cars is less effective. Part of this is the .6 quart lower overall oil capacity, but mainly it's the Rube Goldberg-style, two-step oil-to-water-to-air oil cooler not doing as well as the single-step oil-to-air type. This is something to remember if the opportunity to change to the pre-'83 or 13B type oil cooler presents itself.
The apex seals have no direct contact with the "oiling system", insulated well from any natural lubrication source. Without some form of lubrication, their lives, and the lives of the rotor housing surfaces, would be very short. To protect the seals and housings, oil is provided with each intake charge, either through mixing in the fuel supply, or from an oil injection pump.
This is a multipart question. One issue depends on where you live, the season, and consequent temperatures. This is the choice of weight. Common weights are 10W-30 and 20W-50. When your car left the factory, on the underside of the hood was a decal with instructions on choosing the weight appropriate for where you drive. This information was also provided in your car's owner manual, and can be found in the shop manual as well.
Another issue is the SAE grade. The same places with weight instructions also have grade instructions. However, If you car is several years old, the grade there specified has most likely been superceded. Yours may have had a specification of API SE or API SG. Any oil with a last letter higher in the alphabet than the spec is a superceding oil and has equal or better properties than the oil spec current when your car was built. At this writing, current top mineral oil spec is API SJ.
FWIW, the same weight and grade oil appropriate for a boinger is normally appropriate for a rotary. The primary exception to normal recommendations applies on high mileage engines or those that have been overheated. During normal operation, sufficiently worn oil seals will hydroplane over the oil film instead of cutting through it as designed, according to how tough and thick the oil film is on the side housings. Using a lighter SAE grade can assist the seals to do their job, thus reducing oil smoking and consumption, while a heavier SAE grade can produce the opposite effect. This is contrary to the common recommendation to use a heavier weight oil to reduce oil consumption on a worn engine.
More information on choosing oil can be found with the links in the index.
Other rotary oil choice considerations follow in the next two sections of this FAQ.
Mazda recommends against using it in the rotary engine. Who should better know? This has nothing to do with the lubricant properties of synthetic. As a group, synthetics do a better overall job than dino oil, which is why military and commercial jet turbines use only synthetics.
Like jet turbines, there are differences between boingers and rotaries. One is that oil is injected into the combustion chambers to lubricate the apex seals. The consequence of this is that it is desirable to choose an oil that burns as cleanly and leaves behind as little combustion residue as possible, to minimize combustion chamber build-up, to maximize catalytic converter life, and to minimize smoking. Testing oils for these attributes is not something a typical car owner can easily do. Take Mazda's advice and stick with dino oil in the engine.
A properly selected synthetic used in the transmission and differential will reduce friction, reduce running temperature, improve shifting, and extend component life.
They shouldn't, but they do if you have a Mazda rotary. Before you read further here, be sure to read some of the good technical information on engine oils, so that what you don't read following won't baffle you even more.
I've used 20W-50 Havoline for over 20 years. Before that I used Castrol GTX 20W-50 for 9 years. Prior to that I drove boingers and don't remember what oil I used, other than not using Quaker State or Pennzoil.
The reason I switched was I learned of tests that demonstrated a switch from GTX to Havoline resulted in materially reduced oil consumption. Upon making the switch I was able to confirm those results. This is something a car owner can do, but it can take quite some time to collect sufficient data to constitute proof unless the test vehicle(s) is/are already heavy oil consumer(s). A fleet operator could easily do this, but I am unaware of any recent production rotaries suitable for those who operate fleets.
The only thing to account for the majority of the reduced oil consumption with Havoline is its chemical composition must have been more compatible than GTX with the oil control seal o-rings. They are subjected to more heat than any other oil seal in the engine and are the seals that deteriorate and allow that puff of smoke when first starting the engine or when you exit the throttle at high RPM in gear. As they get worse, the start-up smoking lasts longer and longer, and/or the deceleration smoke gets worse and worse, and eventually the smoking doesn't stop. The friendlier your oil is to these o-rings, the longer they will last.
What I did was many years ago. Oil and/or o-ring chemistries may now be sufficiently different to invalidate my experience. That this may be so isn't grounds for me to make a switch. I still use Havoline 20W-50, but I live in the sunshine state.
Different oil brands are constructed from chemically different crude base stocks. Different oil brands are different colors. Before the producers of 2-stroke oils started adding dyes that proved the presence of oil when mixed with gasoline, the highest quality, cleanest burning oils were a color similar to Havoline and quite different from the color of Castrol, unlike one popular Pennsylvania brand with a bad reputation among marine mechanics that was close in color to Castrol. So it may be that an indicator of whether a particular brand of oil may be o-ring friendlier than another may be its color.
The best answer to this is: whatever your owner's manual says, if you have one. If you haven't, read "The Engine Oil Bible", "The Motor Oil Bible", and/or one of the many Exposing the 3,000 Mile Change Myth articles that Google can find for you, and read on here.
In the '70's & early '80's, I didn't regularly change the oil. I just changed the filter every 5,000 miles. I did this following my discovery that this was the recommended procedure for the NSU Ro-80 wankel made in the 1960's. The 12A & 13B engines from the mid '70's would rarely do better than 1,200 miles per quart and commonly did 600-800, so the addition to top off replentished the little bit of additives actually depleted. The oil itself doesn't wear out, but additives are depleted. In piston engines the oil becomes contaminated much much more quickly than in the rotary. Crankcase blowby doesn't contaminate the oil in a rotary the same way as in a piston engine because the pressure level remains relatively constant, with little pulsing - the power/exhaust cycle is continuous, with a new power pulse starting before the exhaust pressure from the last is gone. After 10,000 miles in a rotary, the oil looks better than oil drained out of most piston engines after only 1,000. Chemical tests show similar results. Engines I disassembled after this "unusual" oil change procedure showed only normal wear.
My current procedure here in Florida is change oil and filter each 5,000 miles. This is easy to remember via the odometer, and based upon observation, more than adequate for my driving behavior. This would be a suitable change procedure for any normally aspirated rotary that isn't subject to a lot of short trip (incomplete warm up) driving. What constitutes "short trip/incomplete warm up" driving depends on geography. In the colder regions of US or in Canada, most winter driving probably qualifies as this type and would dictate much shorter intervals, which in turn leads to 2,500 mile or shorter intervals making much better sense. Incomplete warm up allows condensation to remain in the crankcase without boiling off. This depletes oil additives quickly.
Most small 2-stroke engines are lubricated this way, chainsaws and leaf blowers, for instance. So were 2-stroke motorcycles and outboard engines. Then, someone figured out that injecting oil into the intake stream could be more efficient and convenient.
When there is little load, little oil is needed. When load is high, more is needed. Mixing oil with the gas serves this function in a broad sense, as more fuel, and thus more oil, is consumed under higher load. However, there really is much less oil needed under typical conditions, whereas quite a bit is necessary at the highest loads. And, at idle, an engine runs much richer than under most other light duty conditions, but it consumes much more oil than necessary if it is mixed with the fuel. Oil injection simply offers a better match between oil required and oil supplied.
Race cars have different requirements than our street cars:
Mixing oil in the fuel provides an adequate match between oil needed and oil supplied under such conditions. And, one more potential system failure can be avoided, besides a little weight saved.
Another thing to consider on this subject is that less oil than needed can cause excess wear, or even a blown engine. More oil than necessary can cause a blown engine too. Huh? If yours is a turbo, you want the most octane you can get. Oil acts as an octane reducer, so too much can bring on detonation you might not get otherwise.
Those who still want to mix oil in the fuel instead should know that any oil you buy for premixing with your rotary's fuel that is claimed to be a "special" formula probably isn't that special. The same properties that make a highly desireable small 2-stroke oil also make a highly desirable rotary oil: easily mixed and stays mixed with the fuel; burns cleanly, leaving behind few deposits to build up in the combustion chambers or foul spark plugs; and minimal octane reducton.
The most highly stressed racing rotaries run without oil injection have oil mixed in the fuel at a 100:1 ratio. Ratios up to 160:1 are acceptable for less severe racing service. Full oil-rich from the stock injection pump is roughly 150:1.
It depends. If your rotary Mazda is equipped with a turbocharger, all the normal rules about octane apply. Use the highest available octane premium fuel for best power and best protection against the ravages of detonation. You may find slighly better fuel mileage using lower octane, but you need to be very careful about using the available power on lower octane. If you are good at exercising restraint, you can save a little money on a long trip using regular, but it's probably best to stick with premium for normal use.
With all NA rotaries prior to the Renesis and RX-8, the highest octane you should use is US pump (AKI) 87, typically RON 91 outside the US, no matter how heavily your engine is modified. Octane in excess of any engine's actual requirement is always wasted. The issues of purity and additives in more expensive fuels are entirely separate issues. There's no reason not to want either in a NA rotary.
The rotary engine's high turbulence combustion chamber provides a very high resistance to detonation. Its duration of combustion is also longer, remembering that the rotors turn at 1/3 of the tachometer reading, and the slow burn* of high octane is undesirable in it. Pump 80 octane is more than sufficient for most of them. Best power and mileage are usually produced with the lowest available octane.
The NA rotary in the RX-8, due to its sophisticated fuel management system, higher compression ratio, and different port configuration, does benefit from higher octane fuel.
Many serious rotary racers bring their own low octane gasoline to tracks that supply only racing gasoline. From "How to Modify Your Mazda RX-7", by Dave Emanuel and Jim Downing, HP Books, 1987, ISBN 0-89586-383-9, p 47-8:
". . . the best results are obtained with conservative spark-lead calibrations provided the engine is fed a diet of low-octane fuel. The fact that both 1985 and 1986 IMSA Camel Lights championships were won with low-octane fuel is a rather definitive statement . . . ."
So if you want best performance from your NA rotary, you want lowest octane. The lower cost of it is a nice bonus.
* Note - the time allowed for combustion at high RPM is measured in ten-thousandths of a second. Some literature ascribes lower volatility rather than a slower burn as the characteristic of a higher octane value. In contrast, consider the following: From "14-to-1 compression", By David Green, NASCAR Winston Cup Scene:
"One problem that has developed in the 9.5-to-1 engine is high exhaust temperatures, due to a less-efficient burning of 108-octane gasoline in the lower-compression combustion chamber." (emphasis supplied)For more information on octane/antiknock characteristic:
On the street, less than 12 MPG is uncommon, as is more than 30 MPG. Far more typical is the 16-24 MPG range, as few drive a whole tank at a time doing a particular type of driving. Pure interstate cruising generally means 24-30 MPG, depending on model, tire pressure, drafting, open windows, A/C, and cruising speed. Pure city traffic generally means 14-17 MPG, less if it also means very short trips running a high percent with the engine not yet warmed up, much less in very cold winter weather in northern climes. 18-20 MPG as an overall average is very common.
No and No. Mazda rotaries use a bypass style thermostat. When the thermostat is closed, the water pump recirculates the same coolant back into the block without going through the radiator. This allows the engine to come up to operating temperature more quickly. Without the thermostat, the bypass is never closed, and the engine will overheat. An overheated engine makes less power, until eventually it makes no power.
Thermostats are available in 160F, 180F, and 195F ratings for rotaries. For best HP, the 160 is the best choice. For best fuel economy, 195 is usually the best choice. Mazda usually installs a 180.
Usually, for maximum acceleration with street cars, shifting should be done at or near the RPM point that the G force falls to a level that equals the G force available in the next gear. Without a dyno chart, there's no way to be precise in determining when that is for every gear, and it is different for every gear, because transmission ratio changes between each pair of gears differs, both within a single transmission, and among different transmission models. So, the best that can be done is to approximate and experiment.
A good approximate starting point is to learn where your engine's torque and HP peaks lie, as they will be somewhat close to the points where those two accelerative forces match. Shifting somewhere near your HP peak will typically drop your RPM in the next gear to somewhere near your torque peak. The span between the torque and HP peaks usually contains the center or heart of the powerband. HP falls off fairly rapidly after the peak as reached, although typically less rapidly on Mazda rotaries than on most boingers. Since the HP peak is usually a little short of redline on a rotary, shifting it near the redline will be fairly close to best. Exactly where requires experimentation and depends on which gears are being shifted from and to. It also depends on on whether your car is stock, as peak HP will often be at or above redline on modified rotaries. The closer the gear spacing, the sooner the need to shift, as the following table illustrates:
|RPM Drop Example - 1984 12A RX-7|
|Peak Torque 107 lb/ft @ 4,000. Peak HP 101 @ 6,000 |
You can calculate the above RPM for your Mazda rotary by using the transmission ratios found at tranchrt. Simply divide the "to" gear ratio by the "from" gear ratio and multiply by the appropriate "from" RPM.
For related reading, see acceleration testing.
The "piston" in a rotary is a triagular cast iron assembly. Each tip of the triangle is an apex, so the seal placed there is called an apex seal. It is the only moving part that actually comes in contact with the rotor housing. It's rather unique feature is that its position in the engine doesn't allow for lubrication from the main oil system, so some other method of lubricating them is normally provided. Mazda uses an oil injection pump, similar to those used on many two-stroke boingers, to inject oil into the intake stream, thus reaching the apex seals. The consequences of this are that the injected oil is burned along with the fuel, and adding oil between oil changes is normally required.
Along the sides of the rotor, in between the ends of the apex seals, there are side seals. There are also corner seals at the ends of each apex on the side, whose job it is to pickup the function of sealing where the apex seals and side seals end.The apex, side & corners seals combine to serve a function similar to the pistion rings in a boinger. To see what these parts, or other engine parts looks like, visit the Mazdatrix online parts catalog.
With the engine assembled, a compression check is run. To do it "by the book", a special compression tester is required, because a normal tester for boingers is designed to measure only one combustion chamber at a time. Since three rotary combustion chambers share a spark plug, a normal tester will only show the highest reading of the three. The special testers are expensive tools normally only found at dealers or shops that specialize in rotary repair.
Using the special Mazda compression tester at sea level, if the readings are below 6.0 kg/cm2 (85 psi) and the starting system is functioning correctly (cranking speed of 240 RPM), there is a sealing problem. The compression specification drops roughly 4% per 1,000 feet above sea level.
There are a couple alternatives that are a relatively good guide to compression seal serviceability. The first is to simply remove the trailing spark plugs, disable the ignition, and crank the engine over. Listen for uniformity and strength of the hissing pulses escaping from the spark plug holes. If all the pulses don't sound the same, which is a steady and even rythm, or if they are weak, and the starter is doing its job correctly, there is a sealing problem.
The other alternate method is a normal compression tester with its valve disabled or held open. To do this, you must watch the tester while cranking the engine. The readings will be lower than those from the special tester. What you are looking for is relative uniformity between chambers, and minimum variation between the rotors. Using a normal compression tester with valve removed/held open will typically result in readings about 20% under spec.
If you check compression on an engine that wasn't run less than 15-30 minutes ago, you can be badly mislead. Compression must be measured as specified in the shop manual to be properly indicative of engine condition.
Oil will boost compression and allow starting of a so-called flooded rotary, but you can't count on any particular relationship between normal compression readings and those from a flooded engine with oil added.
The basics on this topic are covered in your shop manual and the previous section, but both assume a stock engine. Porting results in lower than stock compression test readings. This is an unavoidable consequence that mirrors use of radical camshaft profiles in boingers.
Most engines end the intake cycle, beginning the compression cycle, after top dead center. The later this point is, the lower will be the test readings. Such porting and camshafts are designed to shift power up to higher RPM to raise total power. At elevated RPM, intake inertia overcomes the late closing to effectively raise the dynamic compression. Test readings of 90 psi are typical of a good running ported engine, while readings around 110 psi are more typical with stock ports. Likewise, minimum acceptable readings for a ported engine are less than the shop manual specification.
The basic simplicity of rotary engine design means overhaul really isn't very difficult, at least in concept. Several parts of a rebuild are either difficult or impossible without special tools, but these can often be borrowed or rented, or with enough talent, you can improvise substitutes.
The best way to learn is to watch someone with experience. Next best is probably "Overhauling Mazda's 13B Rotary DVD", by Bruce Turrentine. One or the other should provide you with enough information to make an intelligent choice whether a rebuild is something you should attempt.
Most automotive engines are 4-stroke designs that use cams and springs to open and close the valves that let in the intake charge and let out the exhaust. Not only do the cams open and close the valves, they control when they open and how far they open, thus affecting the performance characteristics of the engine. Longer open times and higher lifts allow more flow, thus raising power output to a higher engine speed and level.
Most outboard, model aircraft, chainsaw and leaf blower engines and many other small engines are 2-stroke designs. 2-strokes use a series of ports, usually opened and closed by the piston skirts, to control intake and exhaust timing and volume. The port size determines the amount that can flow through it, and the position and size determine when the port opens and closes.
The rotary incorporates the 4-stroke boinger concepts of four distinct cycles, intake, compression, power, and exhaust, with the use of ports unfettered by poppet valves, which are instead opened and closed by the rotor in much the same way as piston skirts open and close 2-stroke ports. The size, shape and position of a rotary's ports determine both the timing and volume of flow through them, the same as in a 2-stroke. By making changes to the ports, you create the same type of effects caused by both porting the heads and changing the cam in a 4-stroke boinger. Bigger ports flow more, and also give the port more open time, increasing both the RPM at which peak power occurs, as well as increasing the peak itself.
"Street(able)" porting, often called extend porting outside the US, simply defines a degree of modification to stock ports that permits satisfactory operation with mufflers, automatics, stock gearing, and common accessories like power brakes, air conditioning and cruise control. The overall port shape remains similar to stock, but the size is enlarged such that the timing duration is extended, almost entirely by delaying port closing. This extension improves top end performance considerably, but creates a negligible increase in overlap with the exhaust cycle. Idle remains reasonably slow and smooth.
"Auxiliary" ports are used by stock 6-port engines, including the Renesis engine in the RX-8. They are positioned in approximately the space occupied by the additional opening of a street port, but close later, have their own runners, and have sleeve valves that close them off except under heavy load and high RPM. Unlike other intake ports, only one auxiliary port is provided per rotor.
"Bridge" porting is the necessarily big step across the line ending generally acceptable street behavior, equivalent to a "race" or "radical" camshaft. An entirely separate port is added to a street port. The new port creates both more port size and approximately 150 degrees of additional overlap between the intake and exhaust cycles. To work well, the exhaust system must have minimal restriction. Otherwise, exhaust back pressure causes excessive exhaust to dilute the intake charge at all operating speeds instead of just at slow speeds. Consequently, legally quiet muffling often results in poorer HP than good street porting. In contrast to a street port, idle speed must be elevated to smooth out roughness and/or prevent stalling. Bridge porting usually results in too much work to drive in bumper-to-bumper stop-&-go traffic.
Making only a small bridge port, or adding the ports only to the front and rear housings, or both, reduces reduces flow improvement potential considerably, with little or no effect on the additional overlap with the exhaust cycle. Since it is the exhaust dilution that is responsible for poor low speed behavior, the net effect of either is all of the disadvantages associated with the additional overlap, with only a portion of the advantages. Some people call such ports "mild bridge ports". Mild is an appropriate term to apply to the difference in HP between such engines and stock, while the increase in fuel consumption and emissions they cause is anything but mild.
"Peripheral" porting is an alternative big step across the line of acceptable street behavior, also equivalent to a "race" or "radical" camshaft. Like with bridge porting, peripheral porting results in large overlap, and consequent poor idle and low speed performance are exchanged for massively improved breathing and HP at upper RPM.
Unlike bridge porting, peripheral ports are not created by modifying the original ports. For Mazda engines, either entirely separate rotor housings made with peripheral ports are used, or a specially engineered sleeve is installed into a modified stock rotor housing.
Porting For Supercharging. Whether for mechanical, centrifugal, or turbo-supercharger applications, ultimate performance is implemented in part through delayed closing of the intake. Boinger cams designed for use with superchargers close the intake valve late compared to other applications, because it is ideal for giving the blower more time to pack mixture into the combustion chambers. The higher intake tract pressure offsets the compression stage's attempt to push mixture back into the intake when the intake is closed early.
The delayed closing of a "street" port is also ideal for improving supercharged rotary HP. Conversely, the massive overlap of "peripheral" and "bridge" ports gives the blower ample opportunity to push intake charge into the exhaust, which is generally counterproductive to improving power.
To learn more about porting and what ports look like, Mazdatrix has a good explanation of the process and some port pictures. Alan Marr had a porting glossary. For a more detailed analysis, visit Paul Yaw's Technical Articles on porting. Port Timing is a chart that lists Mazda rotary port specifications for comparison.
On a related note, you can find out more about the 6-port induction system and the effects of pressure waves on induction efficiency on this Mazda page.
All Normally Aspirated RX-7 13B's are 6-port. RX-7 turbos, all pre-RX-7 13B's, and pre-RX-7 emission-controlled production Mazda rotaries were 4-port. 6-port & 4-port refer to the number of intake ports per two-rotor engine. A 4-port 13B can easily be made using 12A end housings in place of the 6-port end housings. With engines built this way, aftermarket, Cosmo, REPU or RX-4 intake systems are used.
The 6-port configuration is somewhat analogous to a boinger having a two stage camshaft arangement, where different timing and longer duration are used when operating at higher RPM. To accomplish this, the 5th & 6th ports have a longer open timing , which is good for high RPM power. Since the longer timing is bad for low end power, sleeve valves are incorporated to close off the 5th & 6th ports except under high load and RPM. The opening and closing of the sleeve valves is accomplished through sprung diaphram actuators similar to vacuum operated carburetor secondary barrels, with pressure supplied either via exhaust or air pump. The much shorter port timing with the extra ports closed gives excellent low end operating characteristics.
In stock form, the 6-port has much more low end torque than an NA 4-port, but also more top end HP, making the power band broad & easy to use. Historically, best NA power ported comes from the 4-port. The second generation RX-7 catalog from Racing Beat has this to say on the subject:
"We have had little success in obtaining significant power gains from either street-porting or bridge-porting the 6-port engines. . . . "
But, a good intake to match the porting has been a limitation for the 6-port. This recently changed, and definitive results aren't yet in.
|Comparison of Selected Engines' Outputs|
An exhaust manifold specially designed to sustain the combustion process, which reduces emissions of unburned hydrocarbons and carbon monoxide.
An air pump is used to supply additional oxygen via nozzles or orifices at the exhaust ports. The inner portion is shaped to induce additional turbulence, maintain high temperature, and retard flow to the exit, giving unburned fuel additional time and means to oxidize, thus reducing unwanted emissions.
Thermal reactors were the first commercially implemented emission control devices to work directly upon the exhaust, developed before catalytic converters were technologically feasible. At the time introduced, 1970 for Mazda rotaries, they were considered advanced technology. Mazda began using catalytic converters for Japanese and US 1981 models, but continued using thermal reactors in various other markets until introducing the 2nd generation RX-7.
A lighter than stock flywheel is a great mod. It allows the engine to accelerate and decelerate quicker, which is good for fast shifts, better for vehicle acceleration, and easier on the transmission's synchronizers. Starting from a stop, particularly on hills, may require more slipping of the clutch to make up for the lower momentum than is stored in the heavier stock flywheel. It is for such reasons that the lightweight steel flywheels are a great choice. On a Mazda rotary, they generally offer more than a 50% reduction in inertia from stock, but not as radical a reduction as aluminum, which can be up to 80%. They cost less than aluminum and are more reliable in the long term. Starting from a stop on a hill is less difficult than with aluminum.
Stock Mazda rotary flywheels vary between 21 and 30 pounds. Aftermarket flywheels are typically 17 pounds for steel, and 8-11 pounds for aluminum. The actual flywheel mass is comprised of the clutch, counterweight, and flywheel, so the difference between 17 & 11 isn't as big as it appears, while the difference between 17 and stock can be quite a bit more. The reason for the latter is the weight distribution. On stock flywheels, the mass is focused heavily near the perimeter, while the replacements have more uniform mass distribution, making the inertia difference much more than the nominal weight differences would lead you to believe.
The aluminum replacements are actually a composition of aluminum, most of it, and steel, the clutch face and ring gear, and cannot be as reliable in the long run as the solid steel that costs less and probably never will need to be replaced. If your car rarely runs on a genuine road race track or autocross, steel should make you happier overall.
Reliability has to do with the steel/aluminum composition, which repeatedly heats & cools. The repeated heat/cool cycling can separate the two metals, leading to eventual structural failure. On race cars, flywheels are frequently inspected, as engines don't stay in the cars 20K-100K miles between clutches like daily drivers do.
OEM Mazda rotary flywheels, like most 4-stroke boinger flywheels, are two-piece, the flywheel mass itself, plus a shrink-fit ring gear, while replacements are three pieces or more. To install a replacement, a special adapter designed for automatic transmission use is fastened to the eccentric shaft with the same nut used for the original flywheel. The torque specification for this nut, which is 54 mm, is very high, 400-500 Nm or 289-362 lb-ft. The aftermarket flywheel is fastened to the adapter with six cap screws. The adapter is called a counterweight, since it provides the imbalance the engine requires that is built into the stock flywheel.
Use a Mazda puller. It's the safest and most effective method. It's also expensive. Other pullers can often be made to work, but success isn't guaranteed.
First the nut must be removed. The torque specification for this nut, which is 54 mm, approximately 2 1/8", is very high, 400-500 Nm or 289-362 lb-ft. An impact gun is the most convenient removal device. Without an impact gun, you'll need a long breaker bar, or a normal breaker bar with a piece of pipe slipped over the end to provide additional leverage to get the nut loose.
Do not remove the nut! The flywheel is heavy and subject to damaging itself and whatever it hits when it pops off unrestrained by the nut. Simply back off two or three turns from tight until after you've gotten the flywheel loose of the eccentric shaft.
The flywheel and the end of the eccentric shaft are tapered. The puller should provide enough force to separate the two, but a non-factory puller might not be able to by itself. If it won't, a hammer can provide the additional force required. While the puller is exerting all the force you can make it provide, place a thick piece of brass or aluminum against the flywheel nut, and strike it a moderate blow with a heavy hammer, something in the 2-5 lb. range.
All hope is not lost if you don't have a puller. Two ordinary crowbars can be driven in between the back of the flywheel and the rear housing, exerting pressure. This usually won't remove the flywheel. However, with the flywheel under this pressure, use a 2-5 lb. hammer to strike moderate flow to a piece of heavy brass or aluminum held against the loosened flywheel nut, driving the shaft loose from the flywheel.
Most oil leaks are connected in some fashion to the next FAQ subject, o-rings. The oil pan gasket and retaining screws are one of only two other leak sources of any frequency. The other is covered in "oil problems", which explains things that cause and result from oil leaks, and some fixes. Once you've located the leak source, the shop manual will explain well enough how to replace those that aren't self-evident or covered in "oil problems".
Most engines use o-rings someplace or other. Mazda rotaries have several uses of particular significance, here listed in order of decreasing monetary consequence of failure.
There are several others, but their consequence and/or frequency of failure is minor.
1. The engine is a layer sandwich. Each layer is sealed by a pair of o-rings. The outer section o-ring of the joint layer rarely fails, but the inner one is a sophisticated multicomponent part that serves the same purpose as a head gasket in a boinger. The consequence of failure is the same, reduced or lost compression.
Symptoms of this type of failure vary according to the extent. Mild overheating initially may result in no symptoms at all. The first sign of failure is coolant loss. The high pressure in the combustion chambers squeezes by the damaged o-rings into the coolant. Typically this causes the coolant overflow bottle to fill, the coolant level in the radiator to drop, and operating temperature to rise. At first, the overflow will return coolant to the radiator when the engine cools, which is what it's supposed to do, but it won't get it completely refilled. At a more advanced stage, which may happen a few thousand miles after the initial damage, engine cooling after shutdown will draw coolant past the damaged o-rings and into the combustion chambers. At this point, the coolant, combined with lowered compression from the leaky o-rings, will make the engine hard to start and rough running. Once this is happening, leaving the engine off for several days or more can result in a locked up engine, due to rusting of compression seals. If you recognize this problem early enough, it's possible to significantly delay the need to rebuild by using a special cooling system sealer according to Tom Jelly's instructions originally developed by Paul Yaw.
Early production rotaries, pre-1974, cost Mazda and customers a lot of money, because this type of failure was common, usually induced by overheating. Cooling system and o-ring changes were incorporated into 1974 models that reduced this succeptibility to a small fraction of what it had been. 13B-REW engines suffer a slightly higher incidence of this type of failure than had been the case since 1974.
2. Each rotor has four metal seals that serve a purpose similar to the bottom ring on a boinger piston, controlling the amount of oil reaching the compression seals. The back of each one must be sealed to the rotor, and this is done with a very special o-ring that not only must prevent oil from leaking behind the seal, but also must survive the high temperatures in proximity to the combustion chambers. The longevity of these is influenced by o-ring chemistry, oil chemistry, and heat. "Why does my engine smoke when I first start it?" and "Why does my engine smoke when I shift at high RPM?" explain some consequences of this type failure, which can only be properly corrected via overhaul.
3A. These are also used at the sandwich joints, but their job is to isolate and seal part of the path between oil pump and filter. This path includes dowels than align the engine sandwich, so they are referred to as tubular dowel o-rings. When they cease to function correctly, oil pressure forces the oil through the joint externally, where you can see the leaking near either end of the Mazda logo on the rotor housings, and sometimes internally, into the cooling system. Adding transmission sealer to the oil can sometimes stem the flow, but the correct fix is engine overhaul. Failure of these is by far most common on 12A engines using the oil cooler placed between the oil filter and engine block, as this design results in higher oil temperatures than models with air-to-air oil coolers.
3B. This o-ring seals the oil pathway between the front cover leading to the oil cooler & oil metering pump, and the forward side housing. Failure here is nearly always related to improper assembly of front cover to front side ho using, and manifests as unacceptably low oil pressure.
3C. These o-rings seal the oil filter adapter (and liquid-type oil cooler) to the rear engine housing. When they fail, it makes a mess under the oil filter that can cause premature failure of the heater hose that attaches to the block below the oil filter. The cause is the same as for that for 3A above.
4. Non-6-port engine versions have pathways between the rotor housings and the intake manifolds to warm the intake. Occasionally these fail, resulting in an external coolant leak, either creating a small puddle on the top manifold/block joint, or dripping onto the exhaust. Failure here is typically the result of improper intake manifold installation.
If you look closely, you probably also see water droplets mixed in or nearby the foam. If you find either, there is probably nothing you can do to permanently get rid of them. Luckily, you don't need to. A change in your driving pattern to include more driving under high load and fully warmed, and less driving of short trips or while the engine is cold, might do the job. Enough of such a change will do the job if your car is totally stock.
What you see is an emulsion, oil mixed with water. Your oil includes emulsifiers as part of the additive package. They cause water to actually mix into and "disappear" within the oil. To a point, they do exactly that, preventing small amounts of water from congregating in any one place that might result in oil starvation in a critical location. As long as the amount of water doesn't exceed the ability ot the emulsifiers to disperse them, no harm is done.
All engines are subject to condensation from the normal heatup and cooldown processes, the same way dew forms on the grass in the morning. The oil filler tube area is subject to very little oil flow, and very little ventilation flow, while at the same time it is one area highly subject to the forming of condensation. The emulsifier in the little bit of oil in the area forms the foam as its limit to absorb the oil is reached. When the engine gets hot enough, long enough, the water will boil off. Whether this will routinely happen with yours simply depends on your driving patterns.
When you shut off most piston engines, horizontally opposed designs being the main exception, oil drains away from the combustion chambers. This is not the case with the rotary, which leaves small pools of oil in certain locations that can leak from the these areas into the combustion chambers when you turn the engine off. On a new engine this doesn't happen, but as engine parts wear, certain of the seals become less effective. So, this behavior is actually quite normal.
On engines that have this minor and normal internal leak, the result is a puff of smoke when the engine first starts after being off more than a few minutes. The color of oil smoke is bluish-white, but many don't notice the blue cast and simply call it white. Also, a cold engine runs rich, so this startup smoke will be darker from fuel richness than pure oil smoke from a fully warmed oil burner. Within a minute or two this clears up. It is nothing to worry about, unless the nosy neighbors have the pollution police staking out your house when you usually leave for work or school.
When these seals, actually special high temperature tolerant o-rings, cause the startup smoke, they also cause extra oil to reach the apex, corner & side seals when the engine is running. This may accelerate deterioration of the catalytic converters, but it also maximizes compression sealing for best power.
Just be sure never to let the oil level get below the add line. A low oil level can result in an elevated oil temperature, which can in turn reduce the life of the oil seal o-rings in the engine. The only way to replace those o-rings is a complete overhaul.
If you haven't already read "Why does my engine smoke when I first start it?" start there, and then continue here.
The most likely cause of this problem is the same as that of smoking on startup, but at an advanced stage of oil seal deterioration. There is no fix short of a rebuild, but some transmission sealer added to your engine oil might stall the need to rebuild for a period of time. Don't count on it.
The other possible cause is a leaking turbo seal.
A typical story goes something like the following:
It started just fine when I moved it out of the garage to wash it. Ever since I finished washing it, it just refuses to fire. I didn't get any water on the engine.
This isn't good for any engine, but you found the rotary engine achilles heel. You are playing Russian Roulette by starting a cold rotary Mazda engine and not allowing it to warm up completely before turning it off. If you do this often enough, eventually it will happen. It might even carbon lock. Just don't do it. If you must start it cold without letting it warm up completely, let it run at least two minutes. The longer the better.
One: If this happens to you and yours isn't an automatic, one solution is to push start the car.
Caution - Do NOT attempt to pull start your car. Upon starting, your car may lurch. This can quickly eliminate the space between the vehicles, or cause your car to run over the tow cable, damaging either or both vehicles.
Pushing spins the engine faster than the starter can. As long as you haven't done something else to prevent starting, this works quickly and rather easily. A hill also works well if available. When using either of these methods, do not use first gear. Let out the clutch after reaching a speed of at least 10 MPH, preferably more. Reverse will work if the downslope is facing the wrong way, but beware of the considerable additional danger. Using reverse on a hill should be your last resort.
Two: If yours is '88.5 or newer, simply holding your foot all the way to the floor while cranking may get it started. Cranking this way is supposed to disable the fuel injection and may get you on your way.
If yours is a GSL-SE, keep your foot entirely off the go-pedal, and try a burst of repeated extremely short start attempts, extremely short meaning roughly two seconds or less, followed bys a pause of 4-5 seconds in between, and burst meaning 4-10 tries before a longer pause of up to one minute if it does not start. This procedure is ideally suited also to hot restarts when the engine balks instead of starting instantly.
Three: If you have time, simply waiting until later to try can sometimes do the trick. Sometimes several minutes is more than enough. Sometimes a few hours, overnight, or a couple days may be required. Often, no amount of waiting will help.
Four: Lacking time to wait, purging the engine of excess fuel is the next thing to do. With a fuel injected model, you can generally accomplish this by disabling the fuel pump and ignition, easily done by pulling the "engine" fuse or disconnecting the tach lead from the trailing coil, and cranking the engine 20-30 seconds. This process is more effective if you remove the spark plugs first. If you are due for new spark plugs, now is the time to change them. If reusing the old ones, dry them of any excess fuel or oil before reinstalling. If you want to preserve engine compartment cleanliness, stuff some rags in the vicinity of the plug holes to catch the excess fuel. This also serves as a safety function, reducing the possibility of an unwanted fire should an errant spark find the surplus fuel. With a carbureted car, disabling the fuel pump doesn't shut off the fuel supply, so the spark plugs must be removed to purge excess fuel. You can prevent the carb from receiving fuel by either disbling the fuel pump, or, because carbs use a low pressure fuel supply, pinching the fuel line to the carb with vice grips. Flooding is quite uncommon with carbureted engines, and skipping to method Four is generally easier and prudent when they have a hard start problem.
Five: If pushing isn't an option, and Two through Four above didn't work either, getting additional lubricant into the combustion chambers is required. First, make sure the battery is fully charged and the battery terminals are clean. Full cranking power is crucial in this circumstance. If your rotary is carbureted, just pour a small amount, a half ounce or less, of light oil or ATF down each carb throat. Because ATF is lighter viscosity than crankcase oil, it takes less time for the smoke to clear after you start it. If yours is fuel injected, the task is more difficult. Usually, removing the air duct from the throttle body and squirting the oil past the throttle blades is the easiest. You can inject the oil through the spark plug holes, but if you try to use the trailing (upper) plug holes, you have to get the oil to go through the 3mm hole that the spark normally sneaks through, so even though the leading plugs are lower down, they are easier to get oil through. On some models, there are unused intake manifold vacuum ports to which you can easily connect your oil pumper with a short piece of hose.
A typical story goes something like the following:
"It started just fine when I moved it out of the garage to wash it. Ever since I finished washing it, all the starter will do is click."
This isn't good for any engine, but you found the rotary engine achilles heel. You are playing Russian Roulette by starting a cold rotary Mazda engine and not allowing it to warm up completely before turning it off. If you do this often enough, eventually one of two things will happen. Far more common is that you will flood it. The relatively rare, but far more disastrous, possibility is carbon lock. Just don't do it. If you must start it cold without letting it warm up completely, let it run at least two minutes. The longer the better.
Carbon lock is just what the name implies. A piece of combustion chamber deposit, which is made primarily of carbon, has dislodged from the face of the rotor and wedged in between the rotor apex and the rotor housing, preventing forward rotation.
If the engine has carbon locked, the only direction to turn the engine is in reverse. In-car this should be done only one of two ways. If your bellhousing has a hole aligned with the ring gear teeth, you can pry the flywheel through the hole. Otherwise you must remove the starter to use the flywheel ring gear teeth to force the engine to turn in the reverse direction of normal. Mazda makes a special tool for this purpose, part number 49 FA42 065 for manual transmission engines. This tool is depicted on page 23-4 of the '84 shop manual and page 40-4 of the '85 shop manual. Those with a modicum of engineering skill and a weldedr could fashion something similar from a junk starter. Any other in-car method will just compound the problem, further wedging the carbon between the apex and the housing.
Trying to turn the stuck engine with the eccentric shaft bolt will only do one of two things: badly overtighten the bolt, preventing its later removal when the engine needs to be disassembled; or, loosen it, again accomplishing nothing regarding the stuck engine. Trying to turn the stuck engine by pushing or pulling the car rarely works either. You don't have any control if you have to force it that way. Once the engine is broken loose, you don't want to turn it very far without determining if it will again stick going that direction. Once there is some freedom, usually the engine has to be worked back & forth until the carbon breaks into small enough pieces to let the engine turn all the way around freely. Towing or pushing the car in either direction doesn't allow you the use of any finesse.
Booby Traps explains more about the cause of this problem.
First, be sure you have no basic problems. If you are due or overdue for spark plugs, spark plug wires, distributor cap & rotor, or fuel or air filters, change them first, and then go for a retest. Also, you won't pass if you have removed or gutted your main catalytic converter or removed your thermal reactor.
If these are all in good shape and you only failed by a small amount, you may simply have not warmed your car up thoroughly before the test. On converter equipped cars this is essential. The hotter you can get the cat before the test, the better.
Another thing to try is sold in stores like Target, Wal Mart and K Mart, and many auto parts stores. It is sold under various names and comes in a small bottle like Heet or carb or fuel injector cleaner to be added to your fuel tank. Right on the bottle is usually a claim such as "guaranteed to make your car pass" or the like. As long as your engine doesn't have a massive problem, the stuff usually works. Fuel system driers like Heet contain alcohol that does essentially the same thing, but there's no guarantee on the label. Gasohol can provide the same benefit.
"Best" is a subjective term, so this question doesn't have a single correct answer.
If you plan to continue driving your car upon public roads, there may be little you can legally do due to emissions laws. Therefore, this section presumes that you plan to drive your car only where local law permits modifications that affect tailpipe emissions, whether on a public roadway, or "off-road", and that any modifications you do make are permitted within applicable racing class rules.
The following are HP Modification Areas, for NA rotary engines, mostly in decreasing order ot significance, and definitely not in order of what to do first. The fact is, if you have to choose do do only one thing of significant financial consequence, the one and only correct choice is exhaust, which should precede all other modifications, unless turbocharging.
An option to which all of the above apply.
Mazda rotaries in order of increasing displacement:
Synergy is the interaction between various components of the vehicle and/or engine. Some modifications typically have a materially greater effect if combined with other mods. Good engineering results from a combination of parts that work well together, a sort of the total equalling more than the sum of the parts, or good synergy. The factory systems are designed this way, an integrated package that works well as designed and delivered. You can't expect significant improvement over stock from most single modifications, as they violate the package balance, hurting synergy. On NA cars, exhaust changes produce the most noticable and worthwhile change of any single modification. Conversely, porting and intake changes are typically worth little or nothing used with an otherwise stock engine. However, improve the intake, the exhaust and the porting together, and you can expect a new synergy to really whack you in the seat of the pants, in many cases doubling the stock ouput.
Exhaust temperatures roughly 400°F higher than typical boinger exhaust are more than ordinary components can withstand. So, heavier and/or more expensive alloys are required for Mazda buyers to achieve a reasonable exhaust system lifetime. Replacing the original exhaust with standard boinger exhaust components will result in short life, and mostly likely substantially more noise.
Reasons Not To Remove It:
If you use your car where emissions aren't a concern, then you probably are looking for more available HP or you wouldn't be asking the question. With NA engines, exhaust modifications are usually the best foundation for a HP boosting program. The instructions for header installation should provide instructions for air pump removal.
Production Mazda rotary designs prior to the MSP-RE inherently want to send considerable unburned fuel out the exhaust while decelerating. When it does happen, the result is exhaust popping, commonly called backfiring. Over the years Mazda has used various means to minimize or eliminate backfiring. EGI and the newest non-EGI model methods work very well, and all are better than nothing - when everything is working and adjusted according to spec. By bringing everything to spec, you can keep it under reasonable control or even eliminate it. Conversely, you're on your own once you've eliminated "non-essential" components or made various modifications. Depending on what you've done, there may be little or nothing you can do, short of returning everything to stock. Key is minimizing unburned fuel reaching the exhaust. The simplest method is simply depressing the clutch while decelerating.
If your first generation RX-7 left the factory with rear disk brakes, it also had a limited slip. Many people complained about gear whine when these cars were new in 1980-85. Sometimes an expedient fix involved pig replacement, and an LSD wasn't always readily available in reasonable time. So, some had non-LSD replacements. Many years have intervened, so any number of reasons could explain why a car that should/doesn't or shouldn't/does have one.
There are several ways to determine if the car does have one. One is to jack the car up. With LSD, if you turn one wheel while looking under the car, you should see the other going the same direction. With LSD, if you turn the wheel clockwise, someone watching on the other side of the car should see counter clockwise on the wheel closest to him. That's the way they work when new and should work, but the clutches loosen up with use and eventually this test will not work.
Another way to test is to dump the clutch with the right tire on pavement and the left tire in the grass. If you get decent rubber on the pavement, it's LSD.
Another test is to simply jack one rear wheel. With the transmission in neutral, attempting to turn the jacked wheel should show considerable resistance. Without LSD, the only resistance is the little that comes from the gears and bearings.
Yet another way is to pull the fill plug. If your eyes and the light are good, you can see spider gears unencumbered by clutches if it isn't LSD.
Not every racetrack has effectively banned rotaries from competition. Many have via rules that prevent certain modifications that would be required to make power levels comparable to the boingers in the class. Others have noise restrictions that have the same effect.
One obstacle preventing more extensive participation by rotaries is displacement categories. The limited number of rotary engine sizes from Mazda makes a competitive fit within any class a hit-or-miss proposition.
Bracket racing is still widespread at dragstrips. Some classes in some types of racing permit rotaries at a competitive level.
The first generation RX-7 does have a class all to itself, called "spec RX-7", requiring use of the 12A engine. More information on this class is available. There's another spec racing class using a race chassis and stock block 6-port 13B engines.
Do you own a car that you can be proud of? Then spell its name correctly:
|A Rong Weigh||Its
The RX-7 was completely rebodied twice. We refer to the original body style as the "1st Generation". This body was introduced for sale in 1978 as a 1979 model. The last 1st generation model was designated 1985. The "2nd Generation" RX-7, the first restyle, was introduced in 1985 as a 1986 model. The last 2nd generation model was designated 1991. Sales of the 1991 model continued into 1992 until the new, second restyle, "3rd Generation" model was ready in 1992. This model was designated 1993. It remains in production without significant change to the body style. Sales of the 3rd generation in the US ceased when the supply of 1995 models was exhausted.
It is helpful to RX-7 mailing list and rec.autos.rotary Usenet readers for posts to include applicable generation information on the subject line in the form ,  or  indicating which of the generation(s) or combination thereof to which the post applies. [all] should be substituted if the post applies to all generations.
Mazda Rotary models eXported, and model year first sold in the US were:
Note that the RX-7 and RX-8 are the seventh and eighth on this list of eight.
In the US from model years 1970-1978, most Mazdas sold were equipped with rotary engines. The main exceptions were the RX-3, instead equipped with boingers & different trim and called the 808 or Mizer, and a series of boinger pickup trucks with model names prefaced with a B and finished with engine displacement in liters times 100. Up until the introduction of the RX-7, Mazda had produced 930,000 rotary engines. The bountiful supply of vehicles on this list was anything but experimental.
Mazda wasn't selling enough of them to make a profit. This often happens to products that are, or at least many believe to be, technically excellent and worthwhile.
Remember Sony Betamax VCR's? The parallel between them and the Mazda rotary is strikingly similar. The Betamax was technically superior to VHS in every regard except two. First was the inability, for the first several years of production, to record long enough for a tape to hold a whole feature length movie. Because of their technically superior picture quality, they were also more sensitive to wear and maladustment. By the time Sony overcame these drawbacks, VHS had already overwhelmed Betamax in the marketplace. The mass market wasn't interested in the technical excellence, just long enough play time and reliability.
With the rotary, the early problems were poor gas mileage in a market where that was a very important selling point, and seal reliability. Mazda overcame the best part of these two problems by the time the RX-7 was introduced, but the engine's track record had been tarnished. In the affordable sports car market where the original RX-7 was placed, the buyer was interested in technical excellence as part of the total package. So, the early RX-7 did a fairly good job of overcoming the negtives of previous rotary's record.
For what transpired next, no single reason is to blame. In 1979, the RX-7 had little competition. That changed, and so did the RX-7, becoming a more expensive, upmarket car. After a few years, the RX-7 moved even further upmarket, in a market that was shrinking, giving way to practical SUVs. Those remaining upmarket buyers were hard on their RX-7s, giving Mazda warranty expense per car more than double their average. Part of this was really Mazda's own fault, pricing things like turbos at about four times their real value. With sales numbers more like those of an average car, Mazda could have come to grips with the warranty trouble. But, enough people simply didn't put their money where the beliefs were, so Mazda, like Sony, all but threw in the towel when the US government through a hard slider, OBD-2.
In the US, emissions regulations historically were set by individual states, and for the most part they still are. After a period the federal government decided states and consumers needed federal-level assistance on emissions maintenance and passed a requirement for all cars to have an on-board diagnostic system. OBD-2, on board diagnostics phase 2, took effect for 1996 model years. For Mazda to conform to OBD-2 requirements it would have had to redesign the entire emissions control system, an expensive proposition Mazda felt couldn't be justified for a car selling in such low volume. So, OBD-2 was the nail in the coffin for the RX-7 in North America, ending sales with the 1995 model year.
Sony still makes a few commercial variants of the Betamax that are used by nearly every TV station, particularly by their news teams. They even continue two comsumer Beta models, though they are produced in extremely limited numbers that are on dealer allocation. Mazda still continues limited production of the RX-7, just not for export markets. And, rotary engine developments at Mazda have continued, with some remarkable successes that provide encouragement to rotary techies waiting eagerly for the next generation rotary.
For answers to questions less frequently asked or questions of a more technical nature, try looking in Related Questions back in the FAQ index or in The Garage.