I just picked up an '84 RX-7 with an '88 streetported engine in it. I was thinking about exhaust sizes today. The car has on it a full stainless steel 3" exhaust system but I've been told this is too large. Now, my car currently has a custom 2.25" exhaust on it. After reading about a few things, and seeing that the outlet of the RB header is 2.5", I would think that 2.25" is too small for a streetported 13B. The car was supposedly dynoed at 150 RWHP with the 3" exhaust. So, I'm just wondering if the 3" exhaust is holding back performance or not, and if the 2.25" exhaust is too small. What do you guys think?

 

2.25 is too small. I'm not into N/A rotaries. I don't know if a 3" is too much or not. But I doubt that it is hurting the engine.

 

3" exhaust is overkill on an N/A dude... Plus, it'll cut your low end torque down. 2.5" is way good for an N/A

 

It depends where you are measuring the exhaust diameter. The headers and primaries should be about 2" OD. After that, you can gradually make the exhaust larger. It's not good to directly go to 3" OD, but if the pipe diameter gradually increases to an outlet of 3" OD, then that should work fine. Most people seem to have good luck with 2.5" pipe after the header collector, and with 2" pipe after the Y-split on Y-type exhausts that feed into two mufflers. It's actually more accurate to measure the ID of the pipe, but that's probably not very practical for you at this point.

 

It also depends alot on the porting,.. 2.5 inch max is a good rule for a STOCK port car. If the car is ported with alot of overlap and large exhaust ports a 3 inch will make more power everywhere, if its mild 2.5 would probably be better.

 

I have no clue what kinda port job was done on the engine, but I'm guessing its a mild streetport by the power it supposedly makes. The guy I bought the car from said it dynoed at 150 hp at the rear wheels with a full 3" exhaust. Thats about 180 hp at the flywheel. He also mentioned this is before the injectors were cleaned, and he said he noticed a difference in power after the injectors were cleaned.