Hey H8PVMNT,
Just to add to the discussion, I'm probably not saying anything you and many other here don't already know.
Not too unlike the mysteries of camshaft profiles, backpressure is another dynamic that gets thrown around in general conversation - usually about headers and exhaust. Actually "backpressure" will negate the exhaust flow and the power of an engine. What we want in the exhaust function is flow, but with our engines we need optimum velocity and adequate volume. If we go to big on exhaust, the velocity will drop even though the larger tubing will increase the volume. The scavenging effect will drop and the exhaust pulses will "bunch up" and the vacuum the engine needs to get combustion charge into the cylinder will drop - power-poop-out!!
The trick is to get optimum velocity AND optimum volume. In my experience the 22R seems to respond well to header exhaust modifications. My 22REs seem to be more sensitive to exhaust velocity and flow - "backpressure"!
I think it is generally accepted that tri-Y designed header creates better velocity for low to mid range torque and 4-in-1 header design creates more top end RPM power. After selecting the header, the exhaust pipe diameter to cat and to muffer, and the muffler style can have additional effect on optimizing exhaust performance.
Like other topics, this one can be controversial.
Again, that just my worthless opinion and very elementary understanding of backpressure.
Gnarls.
