I am going to be turboed in about 3 weeks. I'm planning on boosting around 5-8PSI daily. I have heard people say go 3" pipe and some other say go 2.5" because its only 5-8PSI. Would it really matter because you don't want any back pressure with the turbo correct? So I can go as big as I want and it won't effect the power? I was planning on 2.75" or 3", or would 2.5 be the better of the three choices.

 

exhaust 3
charge pipes 2.5

 

can u actually go bigger than 3 inches and would it be worth it?

also, does piping size change A/F ratio?

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by eMpAtHy &raquo;</TD></TR><TR><TD CLASS="quote">can u actually go bigger than 3 inches and would it be worth it?

also, does piping size change A/F ratio?</TD></TR></TABLE>

Yes and no. Different piping sizes can affect spool rates, but it doesn't directly change A/F

 

Intercooler piping: larger piping, longer spool times

2.25" for up to 400whp

2.5" for up to 600whp

2.75-3" for 700 upwards


Downpipe/Exhaust
Larger exaust = less back pressure
3" is terriffic... My buddy managed to put out 450whp on an engine with 2.5" dp and exhaust though. With 8psi I would go with what your budget allows. 2.25" IC and probably a 2.5" dp and exhaust... definetely do 3" if you can swing it though on the dp/exhaust.

 

Same boat as you. Planning on turboing and trying to decide between the 2.5" and the 3".

There was a guy in the FI forum that dynoed his car before and after and he gained 25whp or something like that, but I think he was boosting high teens/low 20's so I don't think you'd see those types of gains on only 5-8psi.

Another thing that might factor in is that I've heard with the 3" it tends to boost creep since it can flow better.