Hi,

I am installing a 1800 silvertop engine running standard ECU & map with the original inlet and throttle body. Provding it all runs ok would you expect me to have any issues if I didn't put a CAT in my exhaust system?

Cheers,

won't have issues running without but won't pasIVA or MOT (unless its pre95)

The only issue would be higher emmissions. If you omit the cat Co will be around 0.5 to 0.8. Hcs may just scrape under 200 ppm and lambda sould be the same value with or without a cat. CO2 readings will be a touch lower than with a cat.
Tested loads of escorts and modeos with failing or failed cats and these are average readings where everything is ok bar the cat. It will run fine just may not pass mot/ ivaemmissions depending on age of engine or reg of your kit

My 1996 MK1 Mundaneo (the silvertop) would struggle to pass every year. The engine year is very important, problem with my Mundaneo was that it fell into the stricter emmissions regs by a few weeks!
The car had a fully functioning catalyst, no engine or fuelling issues, was in excellent health, but was always marginal - really marginal.

Balls. My manifold comes out the side of my bonnet so the CAT will have to go on the outside of the car. I can see that lasting about a week before the fudging pikies kindly remove it for me.

Can anyone recommend a CAT that would be suitable and not massive?

Surely not a problem??

The catalyst (two cans) on my Megabusa were only in situ for the MoT test. After and before that event, they were absent.