For some time i've had this silly idea of making a cat pipe with a catalyst bypass pipe built in, and a valve that would bypass it when the revs got above 3000rpm (like Aston Martin seem to do). The electronics would be ok, and I could use vacuum to actuate the valve with a few bits scavenged from the scrap heap.
...only I can't think of a decent way of making a valve in the exhaust pipe that wouldn't wear out/vibrate/leak and wouldn't obstruct the gas flow too much. does anyone have any ideas?
I guess it doesn't actually have to divert gas from one pipe to another, just cover or uncover the cat bypass pipe.
Its worth thinking about I reckon. I'm not sure the performance gain would be amazing (and it would probably confuse the hell out of the engine management), but it would be extremely cool 🙂. Worst case you could just use it once a year to put the cat back in before the MOT.