Hey Guys,

i want to buy a new cat-back system and dont know which one would be better.

Well, there are 2 cat-backs which have my interest.

APEXI GT Spec
HKS HiPower Silent

APEXI is 65mm at the flange to the cat, the piping diameter rises to 85mm at the muffler.. so you can upgrade your piping up to 80-85 mm.

HKS is 65mm at the flange to the cat, the piping diameter rises to 75mm (3inch) but then INSIDE the muffler it gets back to 2,5inch.. so you have no chance on building a full 3inch right?

since i live in germany, it will be difficult to ship the APEXI because of its oversice.. so i have to cut the piping to fit a box, and weld it together again as soon as it gets here, so this is a problem.. HKS can be shipped without any problems and would be a bolt-on system.

What do you think.. is it worth the 0,5inch bigger diameter for the APEXi?
What is the difference in performance between a 2,5inch and 3inch exhaust?
My car is supposed to produce ~ 350whp in future.. how big is the difference between 2,5 / 3,0inch? 10,20,30hp?? i really dont know

so please help me with my decision!

 

Go 3" with a turbo, it will help with boost response and a few hp.

 

thank you for your answer, anyone else? is the difference that big?

 

Dont waste money on a cat back.


Buy a nice 3" downpipe and then gut out your stock cat. (with the broomstick)

I would for these reasons.

1. More overall exhaust flow(if u gut the cat)
2. Still have the sleeper/ stock look.
3. Probably a cheaper upgrade. Considering your looking at 500$ catbacks and the goodbrand downpipes dont go for more than 300$

 

well, the stock exhaust is rusty like ****, so no chance going with this..
i already have a 3inch downpipe so i need only a cat-back, and will get a testpipe some day.

 

N/A 2.5"
Turbo or Nitrous - 3"

 

stock turbo or smallish turbo 3"
if you are running a really big turbo you may want to go a bit bigger
n/a 2.5

 

For a turbo car 3 inch all the way or Y it off to dual 2.5 inch. I am in the same boat as you are, but I am beginning to make my own system because I want to stay dual and there is nothing available with a properly built Y-pipe.

If you can get the 304 stainless locally I would recomend buying a good muffler, some pipe, some bends and build it yourself!!!

 

Just like the other guys said. turbo 3" n\a 2.5". But if I were you do a full back and after the cat, go to a slightly smaller pipe, then into your mufflers which woudl be bigger. This cause a hyperbola in your exhaust and makes air flow out faster which will probly give you a couple horse.

 

check out the for sale i picked up a corksport full 3 1/8 for 300 shipped. The bigger you go with your exhaust the more low end you lose due to the loss of scavaging. its more noticable on na vehicles, on turbos you want the turbo to be able to flow as much as possible

 

Agreed, if it's turbo get a 3" or bigger, full exhaust from turbo back.

 

thank you all for your replys!

Well, so i have to buy at least 3", well then it should be the APEXI GT.

 

dude 2.5" is fine. I did 250 to the wheels on a 2.5" exhaust... how much power do you plan on? If you are keeping the stock turbo you will be fine with 2.5" . In fact, I think J-rat made over 400whp on the 2.5" racing beat catback. I'm not saying 3 inch won't net you some power, i'm just saying getting a 3 inch exhaust isn't critical.

 

Ive known a few people in the past the simply bought the mufflers they wanted then had a shop bend the piping to make theirs. SAVED HUNDREDS $$$$$$ I know one FC that had 3" down with a 3" single to a N1 was $125 installed.

 

ghetto custom setups with crush bends and ebay N1 knockoff mufflers sound like ****.

 

hey guys, do you know where i could get 85mm ID flanges? i need 4 pieces, it would be also awesome if the same shop would carry 85mm OD stainless steel pipes

i would take racingbeat flanges and pipes, but the biggest they carry is 75mm (3inch)

 

Most of the time because they dont have a resonator or presilencer