2 1/2" bore to 3" bore exhaust worth doing?
07-02-2010, 07:21 PM
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2 1/2" bore to 3" bore exhaust worth doing?
down pipe and turbo location on my escort and cause me problems failing on the 6spd gearbox mount so now need a new downpipe and manifold modded, its it worth me going 3" bore? what power will it restrict me? its a t35 on a zetec turbo btw, cheers
Last edited by rst in breaking; 07-02-2010 at 07:24 PM.
07-02-2010, 09:21 PM
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Yes, theres no hard and fast rule though, you could make 500bhp on a 2.5" exhaust. But if you went to 3" you might gain 50bhp. I'll put up some flow tests of some of the 2.5" and 3" exhausts we make to show the difference when i get home.
07-02-2010, 09:30 PM
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Ive just made a 3" down pipe for the S1, thought the bigger size would help with the flow as it has to make some tight bends. From the sump back its 2.5". 
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08-02-2010, 12:28 AM
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500bhp on a 2.5" exhaust...LAWL
2.5" iirc starts to becomd restrictive at 280bhp (Im fairly sure)
at 500bhp i'd be wanting a 4" downpipe and twin 3" pipes!
Ask yourself why cossie uprated (mongoose/scorpion/magnex) exhausts are 3" from turbo back.
2.5" iirc starts to becomd restrictive at 280bhp (Im fairly sure)
at 500bhp i'd be wanting a 4" downpipe and twin 3" pipes!
Ask yourself why cossie uprated (mongoose/scorpion/magnex) exhausts are 3" from turbo back.
08-02-2010, 10:22 AM
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Although you might need 1200bhp to do 150mph in the lorry, it is possible. In the car it might take just 300bhp. The law of deminising returns applies.
We actually made 491bhp on a dyno dynamics rolling road on a 2.5" exhaust. We didn't go on the rollers after it was changed as the spec was changed totally, turbo, exhaust etc etc. I've no doubt we'd pick up a tonne of power, (a max of about 50bhp as it was on a GT30).
The exhaust design plays just as big a part as the size. A well made mandrell bent exhaust taking the straightest/shortest route possible could be better than a 3" exhaust twice its length with crap bends everywhere.
08-02-2010, 10:44 AM
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I didn't want to go too indepth but heres a simplified version. Think of the fluid dynamics of an exhaust as areodynamics of a car. If you get a lorry, (large frontal area and terrible CD, compare it to a road car, much smaller frontal area and much improved CD).
Although you might need 1200bhp to do 150mph in the lorry, it is possible. In the car it might take just 300bhp. The law of deminising returns applies.
We actually made 491bhp on a dyno dynamics rolling road on a 2.5" exhaust. We didn't go on the rollers after it was changed as the spec was changed totally, turbo, exhaust etc etc. I've no doubt we'd pick up a tonne of power, (a max of about 50bhp as it was on a GT30).
The exhaust design plays just as big a part as the size. A well made mandrell bent exhaust taking the straightest/shortest route possible could be better than a 3" exhaust twice its length with crap bends everywhere.
Although you might need 1200bhp to do 150mph in the lorry, it is possible. In the car it might take just 300bhp. The law of deminising returns applies.
We actually made 491bhp on a dyno dynamics rolling road on a 2.5" exhaust. We didn't go on the rollers after it was changed as the spec was changed totally, turbo, exhaust etc etc. I've no doubt we'd pick up a tonne of power, (a max of about 50bhp as it was on a GT30).
The exhaust design plays just as big a part as the size. A well made mandrell bent exhaust taking the straightest/shortest route possible could be better than a 3" exhaust twice its length with crap bends everywhere.
08-02-2010, 12:37 PM
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how come when i first got my escort it had a standard down pipe then 3" bk. it would only make 1.3 bar boost. i changed the exhaust to 3" turbo bk and it then made 1.6 bar boost. surly you need bigger bore to make more power (get the gases out).
08-02-2010, 12:38 PM
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08-02-2010, 04:11 PM
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havent the money atm so was either going to mod a s2 down pipe ot buy the bends and make it but prob just mod a downpipe and see if im happy + its a mk4 exhaust so tail piece sits wrong lol, thanks anyway
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