im have a werid surging issue over 36 psi the car wont rev past 8k but if i turn the boost to about 30-33 i have no issues. my current setup is

10:1 motor stock head with fp5rs bc valve springs and retainers FF 6765 3in exhaust 3in ic piping 4.5in IC id2200cc injectors modified fullblown housing with two walbro 400 E85 pumps i have old school magnus intake manifold still with stock throttle body i think maybe the stock throttle body has something to do with it but im not sure.

i just want to put the money in the right direction instead of buying more things i dont need the car is currently making 706 @33psi with the way it is now

 

If you're trying to make more than the 706whp you're at, you will benefit from a 3.5" exhaust.

 

There are plenty making 800+ with 3" exhaust

 

Yes, 800+whp can be done with a 3" but even those become restrictive at those power levels.

 

your right. but i think it maybe causing alot of back pressure. im goin to try and remove the cat back to see if it fixes my problem

 

i wonder what the gains would be if i did change

 

This is a very good idea, pull it off and try to up the boost and rev it out.

 

There are alot of high power cars on a 3" exhaust. But the question is always out there.. How much more efficient would it be with 3.5" or 4"
Not sure if you ever saw this article, the supra has alot more displacement but the testing is there..

http://www.modified.com/tech/modp-11...ust-test-tech/

 

This article was the 1st thing I thought of as I remembered the Supra made massive gains from doing the swap. I still think an Evo would be nowhere near those gains but the OP taking the exhaust off should answer his question and I'm interested as well.

 

Both of my cars run a stainless 3" downpipe to 3.5" aluminum exhaust. What it's worth I don't know, but its bound to be worth more then 3" to some extent

 

Needs to be bigger for peak performance. What we force cars to do with certain parts vs what they can do with the right parts are 2 different things. This isnt exactly apples to apples but we went the other way to see once what the losses were.

Took a car with an HKS exhaust (not the freest flowing 3" as it has 2 2.5" resonators) and a 3586, made 535whp and spooled at 4k. Put a stock catback on it (2.5") with a testpipe dump (60mm) and lost 20whp. Okay so 20whp in a 1/2" isnt too bad right? It also spooled a full 1000rpm later.

Backpressure is the devil and must be eliminated for a proper combo to work correctly.

 

im going to set the boost at 36-37 and see if it will rev past 8k

 

I read that your car has standard Brian Crower springs without thick seats and not beehives or dual springs. Maybe valve float at that rpm.

 

i dont think its going to be huge like a supra with a 3L, our cars with a 62mm turbo or bigger i could see us gaining but will it be worth the cash to switch it out tho?

 

so your saying by switching to a bigger exhuast i may not only gain hp but it may have faster spool up?