Doc

A simple question that I could probably answer by getting under my car. However its cold, wet and the car is at the bodyshop having the mirrors colour coded.

How many catalysts do I have in my exhaust system?

If there is only one, is it in the downpipe or the main part of the exhaust?

The car is a UK MY98 with a standard exhaust.
I am considering a scoobysport downpipe as well as a rear box but don't want the hassle of refitting a catalyst for the MOT each year. (Its not for another 13months )

Will it pass the emissions test at MOT time?

Andrew Dixon

There should be two cats on your car. One in the downpipe, and one in the centre section.

According to Scoobysport, removing the centre cat will not cause problems at MOT time (some STis come without this cat anyway), but removing the downpipe cat may well cause MOT problems.

I think that there is a higher flow downpipe available that comes with a performance cat. Might be worth investigating?

A recent survey on the IWOC list didn't turn up anyone who was willing to say that they had got there SS downpipe equipped car through an MOT.

Andrew

Andrew

James_Harvey

You have two cats, the main one is in the downpipe and a smaller one in the centre section.

You can replace the centre section and pass an MOT, however you cannot remove the one in the downpipe and expect to pass.

An alternative is the PE system, they offer a freeflow downpipe plus centre section with sports cat that does enough to pass emissions.

James.

Doc

Thanks for the replies.
I think I will fit the backbox and leave the frontpipe as it is for the time being.

A free flowing cat in a downpipe does sound interesting though. I'll look into the PE system.

pat

AFAICR, all UK spec vehicles have two cats, one in the downpipe and one in the centre section.

You can safely remove the centre section cat and still get through am MOT. If you replace the downpipe then you might still get through an MOT.... run the car, very hard ,just prior to taking it in so the centre cat heats up. Get them to measure the emissions immediately. Alteratively, find a garage which will turn a blind eye in return for a reasonable quantity of cash or alcoholic beverage...

Removeal of both cats will give an additional increase in performance, better fuel economy and a WRC soundtrack...

Cheers,

Pat.

Pete Croney

We tell all of our downpipe customers that it will fail the MOT.

Two customers have got through, but they got the centre cats very hot.

Talk of cats etc is very interesting and we have done quite a bit of work on this...

1) Subaru cats are very efficient and just removing a cat does not do very much, performance wise.

2) All cats need to be hot. "Light up" temp for cats is approx 650degC. To pass the EC new car emission test (BAG1) the cat has to be working within seconds of the engine being started, which is why it sits just behind the turbo. To bring down the "light up" temp you need a greater surface area, which increases the restriction.

3) We have yet to find a "sports" cat that has substantially better flow caracteristics than the OE ones. Rockwell are probably the most technically advanced cats available (with a price tag to match). These offer virtually the same flow resistance as a Subaru cat.

4) If the exhaust system is very hot, the centre cat will be working. A "fast idle" test will have it hot enough, but a slow idle speed gas test will not. In many countries (EU included), the engine speed is not specified in the test requirements... so it passes. In the UK the car has to pass a slow idle test too.

alistair

Pete,

That may be the current advice to customers, but when I bought my downpipe I was definately told that the centre cat was enough. I even left my downpipe with you as I thought I'd never need it again ! This was in the early days before it was an official product, but I'm sure I'm not alone.

There will be a lot of people needing MOT's at some point so is there any way of improving the centre cat performance eg. keeping it hot with exhaust wrap ? Alternatively would a different cat in the centre section be any more efficient, we could club together and have a comunal MOT cetntre section that would be easier to swap than the downpipe ?

Alistair

Steve Howat

In fairness to Pete I have just bought the downpipe and centre section from him and he did advise me about the emissions, which is why I opted to go for broke and get the mid section as well. It also says about emission laws on his website. I intend to take the car to a friend at the garage and have the emissions checked after fitting the sections just to see how good/bad it is but I will probably refit the downpipe come MOT time anyway.

ransj

A friend of mine owns an MOT test station and last week when I was there I had a flick through the MOT testers manual issued by the VI. One interesting thing I noticed was about the HC and CO testing.

The manual stated that if a car passes one out of either the HC or CO test at idle but FAILS the other at idle it can be retested at a higher speed and if it passes then it is considered to be an MOT emmissions pass.

I will try and get a copy of the relevant section from the manual over the weekend as this may be of use to some people.

Simon

[This message has been edited by ransj (edited 22-10-1999).]