What Size Exhaust?

[tm_r33]

hi all.

in the process of finishing a project. its an rb 25/30 with a gt3582 hanging off it with big cams and fuel system and going to be looking for above 400 rwkw at 20- something psi..

so i have fabricated up at 3 inch mandrel dump to match the 3 inch outlet on the back of the gt35 and plan to run open pipe the whole way through. it will all be mandrel bent.

Is continuing in 3 inch going to be large enough or do i need to raise to 3.5 or 4 after the dump or once i get past the firewall????

if u need to know specs on anything else to help inform me of correct exhaust sizing then feel free to ask. car has been built from absolute scratch to use as a track car so nothing is really standard and i dont know if any other factors will come into play.

thanks james

[abr33]

Im not sure but if your running or plan to eventually run e85 you might want at least 3.5 or 4 inch, assuming plumbed wastegate. Otherwise rb30 hybrid dyno thread :-)

[SiR_RB]

i would go from the 3" turbo outlet up in size after an inch or so to 3.5" all the way through, if noise is an issue i would also add 3.5" mufflers with no step downs in size.

[tm_r33]

noise is not a factor. track only. running a 50 mm gate that will dump to atmo at bottom of firewall.

i was thinking i would need to step up to 3.5. can i get a stainless reducer type of thing that goes from 3.5 to 3 inch perhaps?

im building the car myself so very much appreciate people contributing their knowledge. its very near completion but i like to research my options before i purchase/fabricate/assemble things.

thanks for the input guys, keep it coming. will check that dyno thread too! i do not watch the forums avidly so i do not posess the wealth of knowledge that many of u ppl manage to spunge up out of this forum lol

[R31Nismoid]

From the 3" outlet, flare straight to 3.5"

Keep the gate ATMO, and no problems. If you plan to plumb then you'll need to think about 4"

[tm_r33]

thanks ash. where do i find a stainless piece that flares from 3 inch to 3.5 or do i need to fab it myself???

gate will def be atmo.... just so i can crack gate and have screammer pipe and get da bitches jokes.

thanks guys

[r33_racer]

You can readily get 4" to 3" concentric reducers. You can use one of them and trim it down to suit the 3.5" tube. Any stainless steel supplier will have them, i.e Midway Metals, Fagersta or the like.

[Deano 1]

I cant see how 3inch straight though is not enough? The gate is to atmo so under full load a large amount of exhuast is just going to be flowing out the gate........

[Mitcho_7]

I wouldn't want to build a dirty 30 with a gt35 on it and then not have it perform up to my expectations just because i decided to skimp on the exhaust side of things when I was told 4" would be best suited...

[black bnr32]

http://www.modified.com/tech/modp-1102-exhaust-test-tech/index.html

not sure how important ground clearance is to you, but its something to consider. my 4" system has about 3" of clearance at the rear axle area.

[tm_r33]

Its not that i want to skimp or save money. i just dont know if 3 inch is big enough. no point making ita droney 4 inch if its not required. ok so i will try find a concentric reducer this arvo.