is a 3" exhaust big enough???

[Dr Boost]

Is there much gain in fitting a larger than 3" exhaust?

I saw in speed magazine they did a tuners guide for the rb25det. a lot of the shops they talked to said they fit 90mm exhausts.

Does anyone reckon it would be worth the extra expense?

Lifes short, boost hard.......

[EVOIV]

Really depends on your application? I believe too big an exhaust will result in you losing too much low end torque because there's not enough back pressure. But it will be better flowing at higher revs? I think most people can get away with a 3" and still make great power.

[MRK25T]

ive got a 3" exhaust with about 10 small holes along it. Will it make much of a difference?

[akeenan]

3 inch 3.5 perfect

[Warpspeed]

Well it depends on how much gain in noise you want.

A three inch will certainly give you some gain, but a four inch pipe will make much more noise.

A five inch pipe will gain you even more noise still, especially if you run no muffler.

[akeenan]

this is not always the case! .. you could make a 1 inch pipe very noisy too.

[MRK25T]

Originally posted by akeenan

this is not always the case! .. you could make a 1 inch pipe very noisy too.

does it depend on harmonics and the length of pipe etc?

[Talej]

nah mate you need at least 5" for your needs

[GTR R32]

from my experience, the less restrictive your exhaust is the sooner you will make boost. Therefore the more low down power you will have. The top end goes without saying.

so if you aren't worried about noise, the bigger the exhaust the better.

[Edge]

Is there much gain in fitting a larger than 3" exhaust?

I saw in speed magazine they did a tuners guide for the rb25det. a lot of the shops they talked to said they fit 90mm exhausts.  

Does anyone reckon it would be worth the extra expense?

Lifes short, boost hard.......

Having asked the same question a while back here is what I learned.

For RB25DET

A 3.25" would be ideal - will give you a very small gain - maybe 1-2%, over that there is less than 1% gain to be had.

There is far more competition in 3" mandrel bent exhaust which is plenty because you can keep the air flowing through this size pipe without cooling down and slowing too much this way.

Simple answer, money for power its not worth the $ over 3" exhaust.

I know you want the best but 3" is 98% best for 2/3 the price and you could contribute to a turbo upgrade instead with the $ you save.

[Edge]

ive got a 3" exhaust with about 10 small holes along it. Will it make much of a difference?

No effect likely - if anything the velocity of the air in your exhaust pipe will decrease and the gas start to cool and become denser and move slower, increasing pressure toward the back of the exhaust.