The best way to state this is that any changes to the exhaust from the cataytic converters forward (or intake) system will alter the emissions of the engine and are therefore illegal on all public roads anywhere in America. The only legal change is the rear muffler and the pipe in front of it. **All Exhaust Systems/Headers Etc. Are Listed In The Racing Section*
Now that the above has been said, the key to obtaining power from the rotary engine is first and foremost in the exhaust (for racing only, obviously). Any changes to the intake and/or engine ports will not reach their full potential if the exhaust is not done first, or at the same time. If you are on a budget, or need to do improvements in stages, the exhaust MUST be done first whenever possible.
There are many systems and pieces on the market for Rotarys. We have seen and/or tested virtually all of them, and only offer those we know work well and will LAST. The exhaust heat generated by a rotary engine is TRULY IMPRESSIVE. If the first muffler is not packed with stainless steel material it will not last. We have measured the life of some front (non-stainless) mufflers in MINUTES or BLOCKS DRIVEN. Standard type "Glass Packs" used as front mufflers normally last between a few hours to a few weeks. "TURBO" rear mufflers (obtained from local speed shops) actually work reasonably well as rear mufflers, and seem to last around 6 months. If you insist on using this type, at least try to fabricate your system such that they are easy to replace frequently.
For 79-92 RX7's (non-turbos) the most cost effective, easiest installation, and most horsepower gain thru the full RPM range is the TWIN PRE-SILENCER SYSTEM.
IT FITS! The tone is excellent and life is still not determined because none that we know of have burned out yet. Those of you with non-RX7's can essentially duplicate this system by buying individual pieces and having them welded/bent/fabricated to fit your car. We decided on RX2's, 3's, 4's, Cosmo and Rotary pick-up's it was easier to assemble individual pieces.
If you are unable to afford the complete system, considerable power can be gained by just installing headers and a pre-silencer as listed in the Racing Section.
We have found that on 86-92 non-turbo cars, if only a header and pre-silencer are used in conjunction with original equipment rear mufflers, the resulting system is just way too loud! If the Racing Beat cat-back (16420) is also used, then the tone is usable. This combination is our "single" system part #16-MZTX-0020RB. We have also tested the six-port actuators on 84 through 92 6-port engines, and found them to need about 2psi to open. The best opening RPM we have found is right about 3400 to 3600 (relatively stock engine). A single pre-silencer system generates enough back pressure at the pre-silencer to open the actuators, but a dual (side by side) system does not. Our dual systems provide actuation from the front exhaust port, which works excellent. We have tested systems available from other suppliers, and found them to either open too late, or not at all! Also note that the 89 through 92 cars use the air pump to actuate the 6-ports. Our method allows you to either leave the air pump active, or remove it.
Another test we did was on rear pipe and muffler diameter vs. power for the 86-92 non-turbo cars. We found that about 2" O.D. was the largest acceptable. The larger diameter pipes were giving very little gain above 7000 RPM, and were killing the power in the 2500 to 5000 RPM range.
We finally located a supplier of after-market catalytic converters that had acceptable quality, AND covered enough of the RX-7 range, that we could offer them to our customers. The converters listed later in this section are 50 STATE LEGAL, and work quite well. Many of our east coast customers were in dire need of affordable replacements, as theirs had simply rusted away, they were well beyond the 50,000 federal warranty on original converters, and really could not afford the over $2000 bill their local dealer wanted to replace them all.
All of our rear mufflers, and "cat-back" systems, are of considerably better construction than the original mufflers and pipes. The horsepower increase is anywhere from 5HP to 15HP over stock mufflers, depending on the application. They also last longer, and give a much better tone - lower, and without the "metallic" sound.
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