hi guys no doubt this subject has been looked at plenty of times but i couldn't see anything recent.

my question is has anyone done any back to back testing with larger exhaust sizes over 3 inch, ie dyno tested before and after, if so i would be keen to hear, also what power and boost levels are you talking.

i read a couple of articles where some guys with supras netted some fairly large/ hard to believe gains going from 3-3.5 inch at around the 700whp mark.
i am making 800whp and wastegate is plumbed back, i am thinking of making a 3.5 inch dump for the turbo and a separate one for the wastegate out the front bumper for racing, if it is worth the gains so this is me doing some research.

no offence to anyone but i am not interested in all the internet experts opinions i would be very interested to hear facts though

 

I have data that shows ~40hp loss when running with a full exhaust vs open downpipe at ~700whp.

Relatively speaking, my car will make ~700whp at 30psi with the dump open and it will need ~33psi to do it with the exhaust on.

 

I think one of the big dog evo threads on evom, showed gains from going to 4inch exhaust/downpipe. i want to say it was junkbox joey build, he did a side exit 4 inch or something and made more, i just cant remember if the turbo or anything else was changed.

 

cheers for the replies, surely there wouldnt be much to gain going from 3.5 to 4 when they are both side exit its probably what a meter long. i have a full 3 inch system now with muffler and resonator and wastgate dumps in to exhaust so i am thinking there is a bit to be gained there going to 3.5 side exit, not only that but there is a bit of a weight saving too.

 

sirius evo, i notice you are making some god power there with the 86r, have you tried smaller housings? i am making 790@40psi with the full exhaust still on but on a .82 housing on a fp3794, i did put a gauge on the headers and was just under 50 psi at 40psi boost so i thought that was ok.
i am still running rich though could probably pick up another 30hp leaning it off but want to take it out and run it first.
have you run a quarter yet?

 

A substantial factor in that equation is if the WG is plumbed into the exhaust or to atmosphere. Setups with WG vented to atmosphere have an obvious advantage, and aren't as sensitive to exhaust pipe diameter. And then again, the design of the system, especially with respect to point of entry angles and bends is oftentimes significant.

That being said, I recall a dyno test performed by Buschur on his EVO that demonstrated that so long as the WG was vented to atmosphere, the difference between otherwise identical 3" and 3.5" exhausts was insignificant until somewhere north of 650whp (on his relatively low-reading dyno). This is coming from memory, so feel free to look into it.