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Hey guys

I think there are a few other guys in the same situation as me.

My car came with a 3" HKS cat back system from Japan (it's really really quiet, I kinda want something louder). I have also had a hi flow cat and 2.75" front pipes fitted to the car.

I'm now planning ahead to future mods. I currently have -9s and am planning to put 20psi through them with e85. This obviously means over 300rwkw...

From what I've read, people highly recommend getting a bigger exhaust for anything over 300kw.

But since I've already got a full 3", I wanted to know what kind of gains I would expect to see if i upgrade my whole exhaust to a 3.5 or 4 inch system.

If its something like 20rwkw then I suppose its worth the expense.

But then again I have no idea how much a 4" system costs and where I would find one. I'm expecting them to be around $2000 (dont need a titanium or anything too fancy).

So can people please shed some light on this based on prior experiences.

- Did you upgrade from a 3" to something bigger? If so, what kind of gains did you see?

- Do I need a 3.5 or 4 inch system for -9s with e85?

- Where can I get such an exhaust (online, Just Jap, custom???)

Cheers

Umair

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Purely from a cost point of view, the 3.5" stainless is expensive, from memory the cost per bend was roughly double what I had previously paid for 3" and took a while to find. 4" is more common (i.e. cheaper) but in my case there wasn't room.

There are plenty of threads discussing the merits of big exhausts.

you can get off the shelf 3.5" exhausts.

if you can weld you can make your own, i priced it up from an exhaust shop (this was for a cat back)

This is for a 3.5"

$95 for a donut (get 2 if you want to make front pipes as well)

$39 per M for straight pipe

$350 per custom dimension muffler, in my case 18*12*8 & 17*8*5. obviously an off the shelf size will be cheaper (eg 16*11*8)

$18 per flange (includes gasket)

I have a 3.5inch-3.75inch HKS exhaust for sale if you are interested $400 and it yours. I made 15rwkw gain over my 3inch.

I have replaced it with a custom 4inch turbo to tip and it wasnt cheap! Material alone has gone past the 2k mark.

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