Why do de-catted turbo cars smoke?

[Bargain Bucket]

Why is a de-catted turbo car more prone to smoking at idle? Surely the extra back-pressure created by a cat must be tiny. And I can't imagine a cat can deal with that much smoke? My car smokes badly at idle with the cats off but is fine with them in place.

[MrFlibbles]

My MR2 Turbo was decatted and never smoked...

Is it a common phenomenon?

[David H]

Smoke or condensation/water vapour?

[Bargain Bucket]

It's definately smoke !!! Most Lotus Carlton's do this (sorry, should have mentioned the car before). I've discussed this with 3 or 4 turbo re-mans and they all said the same. Decat a turbo car and it's likely to smoke.

[Mikey G]

What difference does the turbo make apart from its oil seals?
What difference does a decat make apart from reduce restriction?
So what did older turbo cars do that wasnt fitted with a cat in the first place?

Cant see it myself, if your car is smoking there is an underlying problem somewhere.

[Mr Whippy]

Is it something to do with the CAT reacting off some of the oxygen left by running a bit lean when it's closed loop? (low load/throttle/rpm)

If you take off the cat then the engine is running lean with excess oxygen which the cat won't convert, which might end up reacting with something else making it smokey?

Dave

[MR2Mike]

I de-catted my MR2 Turbo and it didn't smoke. Well, not until the turbo got a bit tired about 40,000 miles later.

[stevieturbo]

Cant say its anything Ive ever noticed either.

[combemarshal]

Nope, it shouldn't smoke!
And if youve seen the insides of a cat you'd wonder how the hell anything gets through it, the back presure must be huge!
I'm gonna have mine done away with soon!