Catalytic Converters ! Acceptable or Dire ?

Hi Everyone,
I was wondering if anyone has fitted a new engine in their 40 and has needed to fit catalytic converters. I've no idea what they look like on a 40 or how they effect the power output ? If anyone has photos of a GT40 with 302ci engine fitted with CATS, I'd be interested to see it. I'm guessing that all new GT40's fitted with the new Roush engine and registered in the U.K need CATS ?

I'm debating on whether to go 'old' or 'new' block. Some new castings seem to have advantages over old but I don't want to make a wrong decision, especially if I then face having to put up with an ugly looking exhaust system because of emmission controls for road use.

Problem is my engine build will likely take a year or even two to complete as I'll be doing it along side other aspects of the build and I don't want to go down the 'old' block route, only to find that with the latest 'Green' surge of political correctness, that the Government change the goalposts and I find that I need to retro fit cats anyway.I'd rather build new from the start. I know we can't predict the future, but it would be nice to see if CATS really are acceptable in the looks and performance department or just a dire choice.

Please feel free to throw in your thoughts.

Lynn Larsen

Lynn Larsen

Australia requires cats (I believe) on the cars registered within the last few years. I have seen several photos of these Aussie cars fitted with cats. While I can't direct you to a specific example, they are here on the forum. I'd suggest looking through the Builder Log Forum for Aussie built cars and I'm sure you'll find what you are looking for.


Dimi Terleckyj

Lifetime Supporter
Hi Martin

In Australia we have to fit cats but the dont need to look ugly if they are done the right way.
I have attached a photo of my system.
If you need to see more check my build thread.



Personally? Cat's go in the bin. Anything to hinder my beloved Turbo's spinning past 100,000rpm and 22psi, in fact, goes in the bin ;) My bin is full!
Thanks everyone for their input.
Some nice installations there and just the kind of pictures I was hoping for.

Dave, That sounds crazy mad, but in a good way. :D


Peter Delaney

GT40s Supporter
Martin, looks aside, I would steer clear of them if you have the choice - simply because they get so hot. Temperatures are grim enough in the back of a '40 without having these damn thermonuclear reactors trying to :

- Destroy the rear clip's fibreglass & paint
- Overheat the gearbox
- Self destruct

Kind Regards,

Peter D.
Like you 'race only' system much better Rick! Got my replacement clutch from KEP, so will get car registered soonish I hope.