Retards and Decats

Barks

Barks

Barks

Soldato
Joined
20 Jul 2008
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I know a few mates who have now had their cars decatted, may I ask what the attraction is?

- The cars now sound awful, in fact they sound like old bangers. What on earth is the appeal of having an exhaust that pops so loudly it sounds like a clay pigeon shooting tournament is taking place.
- The fumes are horrendous. Sitting as a passenger in a car with a decat with the windows down is a heinous experience. As is being within 50 metres of the car even at idle.

I really just don't get it and from both the cars I'm basing this post on, the decat has not made the exhaust any louder than before only introduced a horrible banger-esque popping noise. (Focus ST and Cooper S)
 
The St's already popped as standard it was they way they were designed. And the de-cat will give it some more Bhp and make the noise louder mmmm 5 pot goodness.
 
cats have progressed a lot since they were first introduced, a high flow cat is not a massive power sapping restriction. Don't all race cars run cats these days and they have no problems making power.
 
Using a decat pipe the gains (sometimes) and more importantly weight reduction is a quick, easy and most importantly cheap way for some improvement.

Sometimes you might lose some power, sometimes gain but when you look at the cost of other work it becomes apparent why it is so popular.
 
What's the score with decats and MOTs? I thought you had to have a decat to get through the emissions section of the MOT.

Do those of you with decats have to put it back on again once a year?
 
If you are getting fumes in the cabin as the result of a decat, I'd suggest your friend tries fitting it correctly.

The ST exhaust is actually quite subdued as standard, and is hardly offensive with the decat either. This is my next mod.

http://www.youtube.com/watch?v=_6sv629-AUA

Not the best example on over-run, but just listen to it when he drives off :)
 
I run a de-cat pipe on my car which is mated to a good quality 2.5" turbo back system.

If anything, this system is quieter than previous setup of the standard cat, middle pipe and stainless backbox that was on the car before.

No problems with fumes and the car never back-fired, maybe the slight pop occasionally... much to my annoyance actually. I wanted flames :(

I'd say they have a leak somewhere or are using cheap parts.
 
Panzerbjorn said:
What's the score with decats and MOTs? I thought you had to have a decat to get through the emissions section of the MOT.

Do those of you with decats have to put it back on again once a year?
Click to expand...

Correct, when I had my Impreza it was MOT'd by a garage where I knew someone there who was a technician, and he said emissions were not checked on as it would have failed (they knew about the decat). Yes it's wrong but hey.
 
What about MOT time?

I know folk used to do this on pre 91 plates as its legal. Plus added a fair bit bhp due to the cats being so restrictive.
 
scott212 said:
I know a few mates who have now had their cars decatted, may I ask what the attraction is?

- The cars now sound awful, in fact they sound like old bangers. What on earth is the appeal of having an exhaust that pops so loudly it sounds like a clay pigeon shooting tournament is taking place.
- The fumes are horrendous. Sitting as a passenger in a car with a decat with the windows down is a heinous experience. As is being within 50 metres of the car even at idle.
Click to expand...

They've done it wrong. Removing the cat should not make the car either massively louder or smellier.
 
anticonscience said:
My Impreza was fully decatted, that sounded awesome, and I had no problems with smell/making it sound like a banger.
Click to expand...

Likewise, the Evo has a 3 inch system and is decatted but doesn't really affect the type of noise, but perhaps the volume :p

Is a bit smellier, but the trick is not to hang around in one place for too long ;)

Done to liberate power, no other reason. If I could have a quieter exhaust I would.

Panzerbjorn said:
What's the score with decats and MOTs? I thought you had to have a decat to get through the emissions section of the MOT.

Do those of you with decats have to put it back on again once a year?
Click to expand...

Technically yes, but no I don't ;)
 
Begbie said:
What about MOT time?

I know folk used to do this on pre 91 plates as its legal. Plus added a fair bit bhp due to the cats being so restrictive.
Click to expand...

I think it depends on the tester. I know of some people who have passed emissions even with a decat fitted. I have a decat in my 2.5" system and it doesn't change the noise levels by much. The OP just seems a little too uneducated as by what he is saying pretty much all cars before the early 90's smelt, popped and banged and were loud.
 
I have decatted my skyline. A big increase in power (20+ hp) sounds better and quicker spool up on the turbo also less back pressure.

Decatting an NA car is pointless though as it is reducing back pressure which is good for NA engines.
 
stupid kids and decats

a lot of cats now have pre and post lambdas. take out the cat, the second lambda gets unexpected signals and puts the ecu in safe mode. the car is slower and overfuels for component protection hence the banging and popping... stupid chavs.

have you looked down a modern cat lately? honey comb structure. you can see through it easily

i know a guy that dynod his car with oem cat (96 golf) vs 200 cell, 100 cell and then decat

no repeatable improvements at all
 
Dogbreath said:
They've done it wrong. Removing the cat should not make the car either massively louder or smellier.
Click to expand...

If it's smellier then something is wrong but louder I can understand. I swapped back on my old 200sx as with the decat on it was much more droney at about 3000rpm.
 
My Roadster was de-catted when I had the V6 conversion done. The cat was originally from my Roadster's stock exhaust system (from when it had a 1.8 4-cylinder engine) and it was deemed to be hugely restrictive with the gases the V6 was just to force out of it; so out it came!
 
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