Ok, I've already read tons of articles on how reduced backpressure is the key and that you need the 2" pipes for <2L engines to keep the waves moving to help scavenge the exhaust. Yes, I got that.

So... the argument is (which I believe) is that if you totally take off your entire exhaust system, you'll have horrible low end torque. So we put a long pipe. But... How long is really necessary? After all, the muffler eventually vents to open air where the velocity suddenly must slow down due to the sudden increase in volume.

What I'm getting at, is if the muffler is at about the point where the pipe is long enough, then it doesn't matter that you have 3", 4", 6", or 12" outlet on a 1.6L civic **so long as** the muffler inlet is < 2.5" or so. Right?