4" Exhaust Is It Necessary?

[ISLIDE013]

Hey guys

Almost completed my r32 GTR build

Wondering if I need a 4" exhaust or is a HKS Hi Power fine?

Quick rundown im aiming to make anything from 500-600kw at the wheels

I have an rb26/30

Everything built

With a billet s72 (GT42 size) turbo

ATM it has a .81 rear which I'm sure will be too small so probly upgrade to .96 rear.

And

60mm turbo smart power gate externally vented

I was told 4" could just make it laggier with only minimal power gains ? Say 20-40hp?

I have also searches for weeks and have mixed answers

For example a lot of people on SAU believe in running a 4" but then so many people I know including a few GTR owners say 3.5 is good enough but they are not pushing big power.

Also the japs plenty of them running 3.5-3.7 exhaust with 800hp

Really not sure which way to go here

Edited October 28, 2012 by ISLIDE013

[Bronx]

why would it become laggier? the easier the flow the better, it will give you lots of top end room.

is it necessary?

depends, is your engine running 12k rpm? how much boost? total displacement?

how do your extractors flow so on and on.

generally on a 3l engine a 4" exhaust helps quite a bit upwards of 7krpm.

thing is, nowhere near street legal.

[Tai1or Made]

Have a search brahandle, been covered.

[AngryRB]

i went a 3 1/2inch for 320kw, so 600kw's id definitely go a 4inch dump atleast

[ISLIDE013]

Bronx my tuner said something about keeping heat to the rear housing via smaller exhaust which somehow let's it spool up quicker (can't remember all of what he said,he did say 4" let's put more exhaust gasses and shows in top end.

It is 3litre rb30 bottom end not sure how much exact displacement is.

Looking to run around 30psi

Rev limit will only be 8k nothing too crazy.

Head has been heavily ported by 6boost

Also have a 6boost manifold so should flow decent,

And not to worried about the Law at this stage lol all power!.

Tailor made I've done a search and nothing quite as specific to my car specs.

Want to know if "I" should run a 4"

[Bronx]

if your tuner is talking about back pressure for a turbo car, he is still dead wrong, back pressure is for a 2 stroke engine, it has been proven heaps of times that a higher revving car does not need the back pressure.

exhaust and manifold sizes affect whether you have low, mid or high range power, and im 200% sure you dont want the low to mid power range, so bigger is better.

but from your setup, depending on what turbo you are running, for a 3l engine@8krpm, i would suggest the following: 200-400kw 3", 400-600kw 3.5", 600-???kw 4". (you might get slight different power with whatever exhaust you choose depending on the tune)

however, you can always factor in that from where your converter sits, the heat will cool down dramatically, so from there on it suits a larger size than the dump.

[ISLIDE013]

Woopa forgot to mention,

It's a billet s72-GTS rated at 900-1000hp although It has the .81 read so instead of changing the rear I'm goin to sell and go for a precision 7175 from powertune.

And looking to crack the 600kw mark so I'll probly opt for the 4" exhaust straight through thanks to your advice

[GTRsean]

4" with big ass straight through mufflers to keep the noise down if street car....

[Bronx]

sounds nice. hope to see the outcome mate