Exhaust Size Question.

In the light of my power restriction due to my baffle, i have been thinking of changing my exhaust for one that is a bit quieter without a baffle, but i would like to find out just what difference pipe diameter makes to power and noise, my current exhaust is an HKS not sure which one,Edit, just done some searching and now i think it is a Zigan 304 Border Max but has either 3.5 or 4" dia, makes me wonder just what effect the fact that i have 2.5" double decat has, i have toyed with going for a XS power 3" system, as i have heard that they are not to loud and of fairly good quality, i know that having the least restriction on a turbo exhaust is the best way to power but was wondering what is the best workable option as regards size and noise?

Anyone care to comment?

With stock twins a good 3" exhaust will be plenty. Pipe diameter doesn't affect noise as much as the actual muffler/resonator selection does. I have a Tanabe G Power Medallion and it is built well and is quiet compared to most. I like it a lot for street duty. I've had a HKS Ti and it is a loud and resonates in the cabin a lot. I've had a HKS Drager and it is in the middle, not too loud not too quiet, and finally I've had a Greddy SP, it was almost as quiet as stock. All of these aftermarket exhaust were built well and fit good. It's all about taste and the sound you want.

I suppose that i have been thinking along the lines of, all/any obstructions will have an effect on power/noise, so if only at BPU its not going to make a big difference as there will be a restrictor ring in place, but one you go single its going to play a much larger part.

If you have a single, want max BHP as efficiently as possible, and also want to do "quiet" track days, which well over 90% are, then you almost certainly need a specialised exhaust. Trust list some for Skylines, but you'd probably be best going to a UK exhaust specialist and having a split 4 box system made up.

Sounds like it could get quite expensive Chris, i'm not single yet, just BPU+ which prompted the question, but i do not like noisy exhausts, so i guess its going to be a compromise of losses, BHP vs cash.

I was going to try one of the Trust "quiet" exhausts on my Skyline, but have decided to make myself something instead. I can afford to *ugger about with my own car, when things are quiet (yeah, right....), but couldn't justify the ramp time doing it commercially. I fancy something that gives no worries when the noise meters come out. On stock twins the retrictive exhaust housings and ultra tame cams kill a lot of noise, but it's a VERY different matter with big singles and cams with 280 plus degrees of duration and fast lift ramps.