Exhaust Question 3" Or 3.5"

[Liquid]

Hi,

Question about exhausts... I know bigger is better when it comes to turbos....

Lets say i'm running 1.5BAR boost on N1s... making about 350AWKW.

Looking at getting a new exaust n try n keep the noise down in the process.. I'm wondering if i should be going 3.5 from the dump pipes... inch or 3 inch from the cat.

I could be mistaken but I think the stock dump pipes are 2.5inch diameter?

Which would mean there's...

2.5 r=1.25 areax1=4.91 area x2=9.817477042

9.8in^2 area... (seems a bit big but thats what the maths say pi * r ^2 *2 ...)

Now into a single 3 inch ...

3

r=1.5

area=7.07in^2

or 3.5 inch..

3.5

r=1.75

area=9.62in^2

On that alone it would seem that anything less than 3.5 inches is going to be rather restrictive...

However, anyone got any thoughts on changes between 3.5 and 3" setups in terms of noise and power around 300-400 kw?

[Harey]

Im no gtr expert so im not sure what size the stock dump size is. My opinion is anything over 300rwkw and you should have a 3.5" exhaust. If you look through the rb26 dyno thread 90% of the gtrs over 300rwkw have 3.5" exhausts.

[R31Nismoid]

2.25 or 2.5" dumbs, to a merge that is 3.5"

That is what you want.

My "rule" of thumb is this

3" upto 300rwkw

3.5" upto 350rwkw

4"+ 400rwkw+

Im running 3.5", 91dB, will flow 340rwkw without much of a problem.

[r33niko]

3.5 is a good way to go

[(OO)SKYLINE(OO)]

2.25 or 2.5" dumbs, to a merge that is 3.5"

That is what you want.

My "rule" of thumb is this

3" upto 300rwkw

3.5" upto 350rwkw

4"+ 400rwkw+

Im running 3.5", 91dB, will flow 340rwkw without much of a problem.

^^ What Ash said.