Hi guys ,

got a question , like how restrictive would a 2.75" exhaust be ?

would it make such a bigger difference in terms of power within 400whp

cheers

 

With a stock turbo setup there probably wouldn't be a ton of difference vs. a 3" exhaust, but that's just my guess.

 

What's your angle? Getting a good deal? The exhaust you happen to look is that diameter?

 

Depends on your mods. I'd just get a 3" and not worry about it. lol Just my opinion.

 

thinking of changing to the GReddy SE Exhaust which is 2.75" , plan on working towards 400whp , anyone have experience any power restrictions with it so far ?

 

I got rid of my greddy for a 3" system and gained 10hp and 25Lbft, so IMO it does make a difference......

 

thats quite a fair bit of gain there , i'm curious cause Archiebabes achieved 500whp with the 5zigen exhaust which is only 2.5" i think with the FPred

 

that is all can be, because the different design of the exhaust or other circumstances , example weather or dyno etc...
Even some 3" exhaust can be differ in power. But the same design with 0.25 inch difference , it is hard to believe will cause that much difference, if does any on stock turbo with a same set up same tuner etc.

 

There are some guys making good power with the tomei which has the 2.75" neck down at the cat.
people will argue whether the short neck down Vs a whole pipe at that diameter makes any difference.
IMO the difference at 400hp (i assume a stock or Green of BBK Lite) wouldn't be terribly much.. you'll leave maybe 10-15hp on the table as suggested above. Or maybe less?

 

I know its almost a year down but I'm interested in 2 3/4" exhausts but custom made not some Jap aftermarket thing .
I bough 2nd hand a 3" front pipe locally made in Australia and it necks down to I think 2 3/4 to suit the std cat . What I want to do is cut the end off to stay 3" so I can use a true 3" cat .
People that want quiet usually have a resonator behind the cat and this is about where the system could step down to 2 3/4"- either side of the resonator .

I go with the theory that as exhaust gas moves down an exhaust it cools and contracts or shrinks if you like and when it does it slows down . To keep the gas speed up you'd have to decrease the tube size to compensate for the heat loss . I think the situation is different when you tune specifically for full throttle performance because with the engine speed up and on full boost there is no lack of heat or gas speed .
Thing is that road cars are dual purpose because you don't drive them flat out everywhere and the authorities are pretty keen to jump on noisy cars . Also you have to live with driving these cars around built up areas at normal speeds and the boom and drones can be impossible to live with .
So with a mildly modified car thats making say 350 hp and similar torque I'm not so sure it needs an exhaust thats 3'' right to the back .
My theory is that an exhaust thats big at the front has enough volume to keep the pressure low enough behind the turbine to get the turbo to spin up early .
I also think if the size is big until at least downstream of the cat that it can be large enough and high flowing enough to minimise the restriction at that point .

Anyway by my calcs 2 3/4" has about 16% less cross sectional area than 3" so I guees its not that much depending on how much power you wanted to make - and how high you intend to rev it .
I'm aiming to run 17-18 pounds of boost on a 9RS turbo and my priorities are least noise and earliest spool with a 10.5 turbine housing . If that can add up to 350 Hp/350 ft pounds thats great and I don't care if it won't rev to the moon . It is a pure road car after all and I want it quiet and punchy .

Thoughts ?

Cheers A .