View Full Version : Exhaust and decat pipe diameter
I spoke with another member earlier about decat pipes and he expressed an opinion that on a BPU car, you would not notice the difference between 2.5" and 3" pipes. If that is correct, would the same rule apply for a cat back exhaust? Or should that be a 3" version as a minimum?
Where you have exhaust boxes the pipe diameter is more critical than the rest of the system as the boxes cause back pressure. A 3" would be better IMHO as 2.5" may be too much of a restriction through the box(es).
I was thinking that too. So, a 2.5" decat set up going to a 3" exhaust would work OK?
That's what I'm going for matey! Should work fine. Also shouldn't overboost too much (well, not up to 1.8 bar!!)
Are we talking decatted j-spec here? In which case surely it would make no odds as the restrictor plate aperture would be way smaller than 2.5".
Are we talking decatted j-spec here? In which case surely it would make no odds as the restrictor plate aperture would be way smaller than 2.5".
Ah, good thinking that man. I had forgotten about the restrictor ring gizmo. So, does the restrictor ring go into the exhaust? The decat? Or at the join?
Join of the turbo downpipe to the first decat I believe.
does the restrictor ring go into the exhaust? The decat? Or at the join?The decat is part of the exhaust.
It doesn't much matter whereabouts in the exhaust system it goes. Any joint is fine for putting the RRing.
Between the 2nd decat and the cat-back exhaust is easy to get to. Between 1st and 2nd decat pipes works fine too.
Between the 2nd decat and the cat-back exhaust is easy to get to.
That's where I have it.
Would a 3" bore be better to reduce EGT's (j spec)?
And would 3" be better for louder sound if you like that sort of thing?!
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