I personally have HKS Legamax cat back great performance and nice note but not loud. I am about to upgrade to HKS extension kit. It's expensive but the quality is superb.

It's flow and backpressure that matter noise doesn't necessarily equal go

 

Im pretty sure the HKS has 2.75 inch tubing which is less than the 3 inch tubing all of the others have
Bigger tubing = more flow = more go
BUT I honestly dont think it makes that much of a difference with our tiny turbos

 

^Not even that much, 65 mm (about 2.55")

 

The GP Sports Exhaust sounds amazing, only thing is I can't find a distributor in Canada or the U.S. They want $1000 to ship it to Canada, goes by dimension/weight.
Anybody know a distributor for them in Canada or U.S?.
Much appreciated.

OOPS, srry this is a dual exhaust.

 

My AMS single exit sounds real good I have a ur test pipe on it too which made it louder not that that is what I was going for I was strictly trying to get good perormance which was accomplished along with a great sound.

 

I have the HKS Legamax catback. Like said before it sounds and looks great. I noticed a nice little performance increase.

What is the extension kit? Never heard of that before.

 

Extension kit is a replacement 02 housing and downpipe from turbo to cat it is a work of art.

02 Housing has twin ports and is cast from stainless steel.

 

Is that on HKS site? How much is it?