Quick exhaust restriction question, please help

[GTRSOAR]

Hey everyone, im looking at getting an HKS Silent Hi-Power exhaust for my GTR and I noticed that the piping was only 2.5" Dia. Would this cause me to loose performance due to restriction? My current system is 3.5" and 3.0" at some parts. Im still starting the project but eventually my goal is 450WHP next year. I currently have HKS dumps going to Greddy Trust downpipes. Is 2.5" big enough enough or will it cause too much back pressure and restriction? Thanks in advance!

[GTRSOAR]

Oh, I have the resonator taken out of my current exhaust, and I will be taking the resonator out of this system too if I get it. Still would be 2.5" Dia throughout though

[DarkCaporaL]

Where did you get your numbers?

The HKS Hi-Power Silent for BNR32 has 95mm piping (3.7 inch) and 120mm tip (4.72 inch).

However it bolts up directly to the stock cat which I believe is 2.5 or 3 inch? You could just change the mounting point where the cat is if you want it larger.

[GTRSOAR]

Well that's interesting... The owner said it was 2.5" going into the cannon and 4" going out. He sent pictures so I'll Definatly follow up that that.

[DarkCaporaL]

Here are the specs from HKS:

http://www.hksusa.com/info/?id=3519

And on RHDJapan:

http://www.rhdjapan.com/hks-silent-hi-power-muffler-nissan-skyline-gt-r-bnr32-65211

[GTRSOAR]

He has sent me pictures of the HKS SIlent hi power cannon and the pipe going into it. The pipe going into the cannon is 2.5" dia. Im so confused. Not sure how thats possible. Its not a knock off either, it has the the proper HKS etching the Silent Hi-Power etching on it too. Beauty welds too. its legit... Thoughts?

[DarkCaporaL]

Well is it the BNR32 version? Or maybe they made different sizing a while back?

I dunno, all I know is that's the exhaust I have and it's clearly not 2.5"....I just went to double check it on my car and it's 3.5" with 4.7" tip....I also checked with a measuring tape and 2.5" is small as hell.

[GTRSOAR]

I know :P The one I have now is 3.5" straight back to the muffler. Ill stick with it till I find a GTR Silent Hi-Power. His was a GTST Silent Hi-power which he failed to tell me lol.

What diameter does your cannon go down to? I have 3.5" pipe right from my HKS dumps and it seems my cannon goes quite small

[DarkCaporaL]

Which cannon you talking about? The HKS catback bolts to the stock cat so whatever the stock cat size is is the smallest it goes. the piping is 3.5" with either a 2.5" or 3" flange where the cat is (I forget the size of stock exhaust).

The flange can easily be replaced though.

[Speeddm]

I have a GTR HKS system. The cat flange is cut off but that is an easy fix. We were running a 4" electric dum instead. Let me know if you want it.