Small enough to make the motor go rich rather than lean. It's a 10 or 11 inch round by 2 inches tall k&N with an Xtreme lid. As far as I can tell, it's just big enough for the motor as long as I keep it clean. I clean it about once a month and it had been cleaned about two weeks ago, so it has seen a good night of racing before this surging issue came up. It has been dirtyier than it is and still run like crazy.
Nothing interferes with any of the linkage. I had to get the velocity stack style base so it would clear the accelerator pump. And it seems small because it is all I have room for under the hood with a 1" spacer under the carb.