On Sat, 24 Dec 2005 23:45:39 +0000, Dave Plowman (News) wrote
(in message ):

In article ,
Simon Hobson wrote:
Not to mention that to make a cat work properly, excess fuel is burned
to create the right conditions in the exhaust.

Excess fuelling will kill a cat. in short order, surely? That's why you
have a lambda sensor to keep the fuelling constant once it's gone closed
loop?

Not THAT much excess fuelling !

But an engine running on the lean side will NOT make a cat work, the fuelling
has to be very slightly rich - richer than best economy anyway. So
effectively, installing a cat means that the engine has to be set up richer
than it would be for best economy.

But, as I mentioned already, manufactuers were already experimenting with
lean burn engines with significantly reduced emissions AIUI - but since these
don't work with cats, and the regs (AIUI) mandated cats, not specific
emmissions, lean burn got shelved.