There's work going on to make a variable cycle engine- one that can run as a
4 stoke for economy and a 2 stroke for power- looks like they're going to
use a valved 4 stroke and go with a double speed for the2 stroke valve
ops.If there is still some mixing of the exhaust/intake mix, would the 2
stroke emissions be difficult to deal with by the catalytic convertor?

http://www.theengineer.co.uk/Article...on+at+a+stroke
..htm