Teflon

I have been reading a lot about decat exhausts.
Can anyone tell me if power gains can be acheived by knocking out the cats from a standard system?


Cheers

CHRIS_D

teflon

the standard exhuast is in 3 sections, from turbo back:

1.Downpipe (1st & main CAT)
2.Centre Section (2nd CAT)
3.Backbox (std is very quiet)

To remove the CATs basically you replace a section with an aftermarket item

Easiest way is to start by replacing the backbox (to get a better sound) and the centre section. Replacing the downpipe will provide more power as it is the most restricive of the two CATs, however a full decat as it is known isn't legal and will fail you on the MOT, but sounds the best and provides the most power (Approx 20 bhp increase).

there are many aftermarket exhuasts to choose from......

Magnex
Scorpion
Scoobysport
Blitz (V.LOUD)
BPM (LOUD)
HKS (LOUD)
etc, etc....

.......to name a few

Best to do a search and keep your eye on the 'For Sale' forum, as there's some bargains to be had there.

Any more advice, feel free to ask or e-mail

chris

CHRIS_D

forgot to mention......

MOT can be sorted by replcing the centre section with standard one if you have a full decat - worked for me last time

(however, not if you've got a HKS )

chris

Teflon

Chris,
Thanks for the reply.
Just wondered if a DIY job could be done on the standard exhaust with some bhp gains.
Call me tight but I am a Scotsman!
My car is a Leggy Turbo and finding an exhaust is harder than for an Impreza.

CHRIS_D

ahh seen

ive done all my own exhuast changing over, quite a few times now (im a chippy by trade!)

cant comment on legacy exhuasts and availability but i have seen a few on here for sale

chris

SyHightower

iTrader: (1)

its easy to smash them out with a lumphammer and a metal bar.....
if your insurance company dosent like the sound of you changing to a performance exhaust, this is the answer, cos theres no way they would check the inside of the standard zorst....so ive been told.

CataIunya

Ha Ha I saw this thread and Si beat me to it...its quite easy to smash out the centre cat I took some pictures and will post if you want....

Joth

I've decatted my standard exhaust. Not only that, but i cut open and modded the mouth to a full width collector with wastegate splitter, like the aftermarket ones.
I had to cut the whole 'neck' section off above the body of the first cat to do the mods to it. While that was off, i pounded out and removed all of the cat stuff with a steel rod and a hammer, at first, it seems really tough, but its this ceramic honeycomb stuff, after you get the first bit pounded straight through, it breaks away easily sideways. Theres two layers of it, about 2.5" inches trhick each, and they are held fast to the walls by a steel braided netting around them.
My center cat was really just an empty resonator as per the JDM norm, and there was no uppipe cat.
The improvement was HUGE. this was done on my JDM Forester running 10psi boost. How much was the influence of the open mouth mod, how much was the influence of the de-catting? I cannot say, but it was a wonderful (and cheap since I did most of the mod fabrication) effort.

Teflon

Thanks for the replies guys.
If I do a full decat are there any issues with overboosting or other reliability/mechanical problems?

Joth

In my case, the decatting did not affect the boost in any way, it still held 10psi boost with no spikes, even when I moved to a straight flow 2" muffler (very short lived bacause it strangely increased my lag) it was always a steady 10psi.