Under what conditions would a cat be required ?

At the moment "95 and later cat required for car engines. The rules specify a date in "95 so best get a "94 or earlier engine to be sure. Probably all change by next week!

Cheers - couple of questions though

does it go by engine age or car registration year ? or both ?

If it is by registration year, how does a Q plate effect things ?

Assuming you are about to build a Locost, or other kit type car then it's the age of the engine that matters.

When you take your car for its SVA you will be required to prove, by way of manufacturer's paperwork, the year the engine was manufactured in. You don't get to register your car until after it has been SVA tested - so it has no plate, either "Q" or anything else at that time.

If the car already exists, ie. is an old kit, say with a X'Flow, is already road registered and you wish to fit a late (post 95) Zetec you have no problem as the car, being a kit car is MOT tested to a very low emmission spec. - ie is different to a mass produced car, such as the Mondeo the engine may have come out of.

This loophole is highlighted by some of the new bike engined cars who borrow/rent "cats" for their SVA and then give them back after the test!

thanks for the help -

still not totally sure about the kit i will go for but I think (to keep it simple?) I'm going to source a sierra with a 2l pinto and start sorting donor peices while i decide....

Cheers