Exhaust Size

[exXU1]

Would some one please shed a little light on the following.

I would like to know wether a 4" exhaust is going to flow that much more than a 3.5" .

Will it make a lot of differance on a high hp ( 900 ) engine.

What size do most of the high HP GTR run ?

I would like to be able to work out the flow rate some how.

[paulr33]

i would imagine it would make a massive difference.

the less backpresure on the turbine housing the better usually

i think the racepace rb30 gtr has a 4" dump into a twin 3" system. it was in one of the magazines, speed im pretty sure

i guess the ideal way to find it would be to run it on the dyno with the exhaust attached then do another run with it deattached and see the difference, may highlight if its a restriction or not

[Busky2k]

4" is a fair step up from a 3.5". The surface area difference is 30%!

On a 900hp car, yeah you'd want it as big as you can get...

[R31Nismoid]

as stated, 4" above 400rwkw IMO

[Roy]

4" ? Crikey, how do you go with tucking that up the belly of the car? If you need the exhaust flow, then surely its easier to package twins on the underside of the car rather then a biog single???

[exXU1]

4" ? Crikey, how do you go with tucking that up the belly of the car? If you need the exhaust flow, then surely its easier to package twins on the underside of the car rather then a biog single???

Good point Roy!

[Edge]

No it won't make much difference, 3.25" is the tested optimum max size with a GT3040 turbo, so 3.5" should be enough. Sorry I can't remember who tested it.

edit - argh still getting used to the controls of the new forum, lost most of my typing...here goes again.

I like that dual exhaust set up, you should be able to make the car quieter while also getting even better flow characteristics setting it up so that the exhaust tips are smaller but still meet the 3.5" total size. Multiple smaller exhaust tips should create a lower pressure differential and assist flow.

I like this idea, so now I wonder where I can get dual exhaust system from in Sydney? Is there a brand name option for this or is it all custom?

The noise on my car is perfect lower tone (same tone all through rev range, just volume change) but a bit loud on low throttle ie. off boost,

I'm thinking of installing an exhaust valve controller (EVC).

Should I get tuner to set it with the computer to automatically open and close proportionate to the THROTTLE or BOOST or RPM ???

(Anyone have advice on whats best?).

Edited March 1, 2006 by Edge

[R31Nismoid]

No it won't make much difference, 3.25" is the tested optimum max size with a GT3040 turbo, so 3.5" should be enough. Sorry I can't remember who tested it.

Umm, sorry to say but a GT30 is only around the 300rwkw mark.

This is hardly what is being asked here.

What was asked was a 900HP setup, well over 500rwkw

So the above statement has nothing to do with this thread.

Bigger is always better. I cant see how 3.25 was "optimum" as the less backpressure the better. 3.25 would have been the minimum requirement

[PHaT MR30]

what size did you have for your 369rwkw run ash?

[R31Nismoid]

3" actually... on the 104, we only went 270 on pulp and it was carrying on a bit.

Much more and there was mis-firing, detonation... not good

The plan was to change to 3.5"... but then i sold the motor to our mate

[Bl4cK32]

Apexi make a dual cat back system.

Ive got a custom catback -2x2.5" pipes to 2x 3" mufflers. It works out to about the same as a 3 and 3/4" single pipe.

It is quieter, and doesnt drone.

A 3" should be good to 300rwkw, a 3.5" to 350+ but over that id want to flow at least a 4" (or split 3") system.

[Trust33]

Not speaking from any experience here from owning a hi hp car,but,i have been swapping from stock to aftermarket exhausts of late and the power difference is very noticeable.

Even when there is just a silencer in the end of the sporty it takes away all of the fun in owning a sports zorst.because there is that initial surge of power for a split second and then it's like it just returns back to normal power levels.

Id personally go for the biggest zorst u can fit.Especially if you are using it mainly for track duties.

[R31Nismoid]

what size did you have for your 369rwkw run ash?

Oh, and for the RB26, im going twin 2.75" (or there abouts) off the GT-SS/trust split dumps, aiming for 300-320rwkw.

As Bl4cK32 said... you can get it quieter and less drone... hence why im now going twin... noise is only good for so long

[exXU1]

Oh, and for the RB26, im going twin 2.75" (or there abouts) off the GT-SS/trust split dumps, aiming for 300-320rwkw.

As Bl4cK32 said... you can get it quieter and less drone... hence why im now going twin... noise is only good for so long

All intertesting in put fellas , but would like to see / hear of some solid evidence of flow characterisics,eg what volume at X pressure will y Dia flow etc?

[manage13]

No it won't make much difference,

Yes it does! Around 35rwkw difference on a certain setup. Speak to Ben (RACEPACE) yourself if you don't believe this figure.

[Dash]

What size do most of the high HP GTR run ?

The fastest one on street tyres doesn't run one so theres a option.

[180bfj20det]

Bigger isnt always better, its just better than smaller. Going to big adds weight. Fact is in Australia, we chuck 3" on everything from 600hp GTRs or XR6s to 200hp CA18s. It works but for example, the CA18 could make exactly the same power as with a 2.5" exhaust unless youre chasing more than 450hp at the engine. Even most street WRXs are fine with 2.5" exhausts and make no more power with 3" exhausts. All this is within reason and notice I said "most" and "street". Exceptions always exist.

http://www.turbomagazine.com/tech/0212tur_exhaust/

Turbos operate best with no exhaust backpressure (Quote Bell's book) so you can see where the fact bigger is better comes in, but remember there will be a point at which bigger is going to yield no more flow and just add more weight.

Also, surface area is no good for comparison, you need to use pipe volume with respects to resistance, pressure etc which is a fluid dynamics formula. Quite simple really, so dont stress. Look it up on the net

Boosted frog