Have any of you guys got a catalyst-free exhaust fitted? I'm looking at one from SE. My scorpion cat-back is already loudish and I'm reluctant to go louder so is there any difference in noise level? What difference does it have on performance? Mine's a 1990 so I can run it decatted and still be legal, even thru an MOT. True or false?

 

erm, that's false, and true, depending on what you are questioning the legality of.. ;)

 

my 0.02p worth....

 

Legality bit:-

i researched this a while ago, and spoke to someone at the MoT about the issue....

 

The cutoff date for the change over in emissions standard is 31/12/92

 

The emission levels required for vehicles registered before this date are very lenient, and most vehicles, with or without cats, should pass.

 

The emission levels for cars registered after this date are a lot stricter, and it is unlikely (but not impossible) that you will pass without cats.

 

However, it is actually illegal to modify your vehicle exhaust system if it alters the emissions stated by the manufacturer. That includes changing the system, removing/gutting the cats, etc., etc.

 

But, you would have to be very unfortunate to actually be prosecuted for such an offence.

 

Performance bit :-

as i understand it.....

removing the cats makes the turbo spool up faster, due to the reduced backpressure. This will also allow the turbo to flow more air through.

 

Noisy bit :-

depending on how you go cat-less will affect your noise level.

If you just gut your cat, then you get left with a small boom box in your exhaust, which makes it louder...

 

If you replace the pipes with straight through pipes, then you are still getting no sound deadening at all

 

Ideally, what you should get are resonators installed in place of the cats.

These are expansions in the pipe (such as on some performance exhausts) which have sound deadening features on the inside.

 

To be honest, i don't know why down pipe manufacturers don't put these in.

 

I got cat replacements which definatley made the car louder and the turbos spool up more quickly. I also got a few psi more without adjusting the boost controller. With my exhaust it's not loud, but with some makes it's a bit OTT for me.

 

Steve should be able to reccomend the Manufacture, I can't remember, but around £200. The plus point is that you get to keep your original cats incase you need to put them back.

 

MOTs... I have 1991 and only just passed the MOT on emissions. So it's possible. To help passing a test you should make sure the car is hot and has been running just before the emmission test.

 

I would reccomend them as a good value for money upgrade.

 

I have the full SE exhaust fitted and it is fairly loud, but this can be reduced by the additional centre muffler option, I also had no problems with the emmission test as I had to rev the engine before the equipment could even get a reading, and then it passed with ease. The only thing to be aware of is that the removal of the cats will increase the suction on the back of the turbo and if you have weak seals then you will see oil smoke on occassion from the exhausts.

 

I have a late 1992 TT which had the nasty pre-cat :-(

 

I had SE replace that and the other set of cats further down with nice free flowing stainless steel tubing. I found that the car had a bit more growl but it had slightly more driveablity on light throttle. Turbos do spool up nicer with this mod.

 

My rear part of the exhaust is on the way out so I will go for the SE rear end shortly. I shall see how it goes.

 

As MOT's go my first one is up in January (fingers crossed) 8-)

 

Jez, I think if they're the ones I think they are, Steve's front pipes were the SE ones.

 

I have mongoose with gutted cats. Does make a bit of difference on noise but not huge.

 

If Craig gets round to organising this week's meet (?) then if you're local and come along you can hear the comparison as Craig has mongoose WITH cats.

 

Dave