Ok... I have searched for many days, NOT hours days! and have not come across the answer I am looking for. My main question is what would be the max HP that a 2.5 Stainless Steal exhaust would hold on a FI Garret t3/t4 hybird turbo setup? I am doing this on a stock -SE motor starting with 5psi untill I get the additional injectors and a Haltech F5 to handle more boost. My goal is to run 12psi on a Streetported -SE motor with all 93 side seals and 3mm apex seals when I am all said and done. This will be a daily driver so keep that in mind before stating I should go with 3.5" exhaust. Low to mid range would be nice, thats why I was looking at doing 2.5 from turbo back. But I also want to allow for upgrades. So I was thinking to make a 3 peice stainless steel exhaust with a 3" Downpipe, then go down to 2.5" from the DP to the rear. My thinking on this is it will allow for a 3" full exhaust later if the 2.5 will not handle what im putting to the wheels. But my debate on that is boost lag with the 3" downpipe, seeings there is less back pressure. It seems that everyone stresses to put 3" exhaust on a turbo rx7 but many others are finding that it is to big for their setup. I dont plain on driving her above 6k rpm ALL the time, so to have boost start at 4 to 5k rpm wont do me much good. I am still learning as I go with this turbo setup seeings I knew nothing about a turbo charged cars about 6 months ago. Any advice or tips will be great! Please back up your suggestion on what size to go with, or why my idea of the 3" downpipe with 2.5" mid2back piping wont work.
Thanx guyz.....

" This forum rockz for turbo Rx-7z "

 

A full 2.5" exhaust setup is good for about 350 rear wheel horsepower (so i've been told).

I am running a full 2.5" setup, from downpipe through to rear muffler. I have a Racing Beat 2.5" downpipe, and then i took the gsl-se Racing Beat muffler and chopped off the dual inlet and welded up a single inlet. I also have a 2.5" racing beat presilencer in the middle. This is the nicest sounding exhaust i've ever heard. I LOVE it.

As far as flow goes, the larger diameter tubing you have, the LESS turbo lag you have, the more free the air flows the faster the turbo will spool. THe problem with larger diameter tubing is that you will lose engine backpressure down low, before the turbo spools. This is why you'd go with smaller diameter; to help the engine's low end not the turbo's.

The smaller diameter (2.5") will also help prevent boost creep. During normal (safe) turbo operation the wastegate opens at a set PSI (lets say 6 psi), and then the boost goes from 0 to 6 psi and holds. Boost creep is when the boost is too powerful for the aperature size of the wastegate, and after holding for a short while it continues to rise again. This is uncontrolled boost, and this is not good. This can destroy the engine if you get a boost spike or something. So smaller diameter exhaust tubing helps prevent this.

Hope this helps. Any other questions feel free to shoot me a PM.

 

bump....

 

IoTus, you mentioned something about backpressure being needed by the engine for low end power.... I was under the impression that rotary engines didn't need any backpressure, which is why we can run RB headers-to-presilencers-to-PP muffler on a stock engine. Does the addition of a turbo necessitate backpressure? Or are you speaking in General, from stuff you know about 4cyl exhaust systems?

Jon

 

bumpy bump....

 

Come on... no one else has anything they can add? ;]

 

I run a 3in system on a full To4b turbo upgrade. Lowspeed driveablity and stop and go isnt really a problem. IMO a good strong clutch is going ot affect that the most.

you may want to look into a straight TII conversion with original harness and maybe a chipped computer, I would think it would be faster, cheaper and with better drivability. Plus you could get a prefabed 3in downpipe for cheaper than custom