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TECHNICAL NOTICE - Exhaust Catalytic Convertors.

Comp Sec

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I have been made aware of an incident at an event yesterday which resulted in a number of competitors being excluded from the event for not having Exhaust Catalytic Convertors fitted. I am given to believe that the cars affected yesterday were all Q Plates registered after 31/12/1999 so were not required to have a CAT fitted under the MOT rules.

Whilst I am aware that there is an investigation and appeal ongoing over the circumstances I want to understand if it has any impact on any of our competitors.

Motorsport UK Blue book 2019

Section J 5.16.7. Exhaust catalytic converters must be fitted to all petrol engined production based saloon, touring and sports cars, including specialist production and kit cars, manufactured after 31/12/99. They may be specified for certain other formulae. Competitors are reminded of their obligation to maintain such equipment on a vehicle used on the highway where government legislation requires it.

So if your car was manufactured on or before 31/12/1999 a Catalytic Convertor is not mandatory

If your car was manufactured after 31/12/1999 then a Catalytic Convertor IS MANDATORY.

This applies to cars in all our classes.

Please note this rule has been in the blue book since 2009 but I am advised has not been consistently enforced.

We currently only have two cars on Q plates, both of which were manufactured well before 1999.

However I am aware there may be some cars in our championship which may not require a CAT to be fitted under MOT rules but are required to have a CAT fitted under Motorsport UK rules.


If you believe that you are affected can you please contact me ASAP to discuss.

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I've recieved a couple of questions asking how you can tell if a CAT is fitted to a Standard K Series.

Am I correct that unless you have a cat on a can fitted it is normally a seperate unit in the section between the manifold to the silencer, or is it located under the heat shield on some.

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It's under the heat shield on a K-series car with the single pipe through the side skin.  The catalyst is welded to the front of the silencer though so it's pretty obvious.  I'll add a picture in a mo. 

Edit: Ta-daa!  The obvious section that is welded on at the front of the wider portion is the cat'.


Edit 2: Does this mean it's a good time to advertise the couple of spare ones I have in my garage? *biggrin*

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Yes, I was struggling to find that one to post a picture of though.  I figured that nobody would have any difficulty with spotting this one as it's separate to the main can.

Here it is:-



There's also the option of 'cat in can' aftermarket exhausts too of course but there's no standard with these so more difficult to tell.  Unlike the exhaust in the top picture you will be able to see by looking down the front of course.

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I've seen catalysts fitted close to the rear panel of an Evo as the book said nothing about where in the system it had to be and the owner thought it was better having it there.

I would imagine the same would be possible on a Caterham if someone wanted to challenge the regs. From an emission perspective it should be as close to the engine as possible to warm up as fast as it can.

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This in no way helps those of us with custom silencers in which the catalytic converter is fully enclosed inside a single can

Mine is Powerspeed who were pretty popular so there must be plenty of others out there  but sure I have seen other manufacturers as well.

How and where do we get guidance to cover this situation? common sense tells me that you can tell from the difference in temperature between the cat section and the silencer section but common sense does not always win the day (eg camera mounts)

If the scrutineers want some kind of proof then I would rather know now so it can be found rather than bounced out of the event on the day



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I have dug out the invoice for the silencer that I had made a few years ago that has a "Sports Cat" built into the front of the silencer can.  This thread and my local garage ringing me when it went in for it's MoT to ask if I had a cat for the car made me think it may be a wise addition to the paperwork I carry around.

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Geoff's approach with the invoice is a good approach, alternativly  a confirmation from the supplier on what they supplied.

sorry can't provide clearer guidance as while this requirement has been in the blue book for a decade , its not something i've heard challenged. 


If i do hear anything i will distribute

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