just got an rx7

i was wondering about changine the stock exhaust

maybe runing straight pipe, gutted cats

how big or what is the best size of the pipeing?

 

most go 2.5 unless turbo then some go 3".

www.racingbeat.com has what most people on here would call the best exhast for any rotary. check them out. little pricy though but worth it.

 

welcome to the forum. i would agree with the above. also, go with racingbeat!!! well worth the money!!!

 

yes, racing beat is the way to go, great sound, good power, and it lasts like nothing else.

 

what is the stock size of the piping? Will i experience gains if i use 2.5 inch with no cat and stock exaust manifold and stock muffler?

 

That will most likely not do much, you need to replace the whole exhaust to really feel the difference. That's headers and everything.

 

Do not go bigger than 2" piping, you'll lose exhaust velocity thus power. If your engine is street ported, larger piping would be permissable, but your engine will not be pushing enough air on stock ports for anything larger than 2" piping.

This may be hard to understand, but the smaller the piping, the better the flow at lower RPMs due to the amount of air being pushed out the engine and that air being able to keep velocity, once that velocity is lost, you'll start getting back-pressure. As the RPMs increase, more air will be pushed, thus you'll need to gradually increase the diameter of piping for given power band, but when piping is too large for full efficiency of the engine (peak power of stock ports), your engine won't be able to flow enough air for it, thus actually harming flow by creating back-pressure (for the area of peak horsepower on stock ports).

 

i'm not contradicting, but i used to have rb header, straight 2" piping to a high flow muffler. now, i have rb header, straight 2 1/2" piping, to the same muffler. also it's now under the axle instead of the over. all through the rpms it is much better now than it was on 2". and my top end, WOOOOOOOOOOO HOOOOOOO! i actually shift at a lower rpm now because it throws me through the band a hell of alot faster. so maybe it's just my car. i dunno.

 

I believe Mazdatrix had a study on it with Dyno sheets of different exhaust diameters. Perhaps it could've been 2" with stock manifold, i cannot remember, but they achieved maximum power with 2".