Sorry chaps, the question has probably been asked before but i cant fathom the new search and im either getting old threads with dead links or not quite the answer im after.

Im at the end of my rebuild and im starting to think about the exhaust, the car is;

b20 vtec
9.2:1 compression
stock head (for a short while)
Full-race twin scroll manifold and 4" downpipe
GT4088r turbo

My question is, will a 4" exhaust offer much of a benefit over a 3", that question has been asked before. But i am not interested in peak power gains, can anybody tell me whether the 4" exhaust will offer any gains in spool up for the turbo.

Im aiming for as close to 600 (WHP) as possible - safely. I am simply doing all that i can to reduce the lag- and any input or links would be great.

Thanks

 

gonna be hard to get to that goal with that head

 

The 3" exhaust will be fine and you shouldn't have a problem making 600whp on that turbo/setup. I went from 3" to a 3.5" and the different wasn't all that. I have a PT67 turbo which is pretty much the same size as a gt4088.

Adriano

 

Thanks for the feedback- i think ill stick with a 3" then. Was there noticeable difference in lag?

HarfordCTR - the head will be changing before i go for the 600, im doing it slowly. The head will be getting some attention next. I just need to get the car up and running again at the moment.

 

Dont listen to HartfordCTR cause you will have no problem making 600whp. I made 650WHP@23 psi with GT4067 which is little bigger turbo than yours on a stock head with type r cams.

 

Oh thanks Turbocivic94 thats encouraging. I wasnt sure myself but this is potentially good news for the bank balance..

 

Does anybody else have any information on whether the step from 3 - 4" has an effect on lag?

 

No