[BrianMN]

Techlogik- read my post last page. Typical non-performance and non-sophisticated engines need backpressure to run PROPERLY - the reason is NOT for more power or torque. Why do they new backpressure to run Properly? Because they are TUNED to run with the specific exhaust system and the specific backpressure. Our BMWs are smart enough to adapt a/f to changes in backpressure. Many cars (even nowadays) cannot adapt themselves well enough to compensate. Go back to carbureted engines- if you wanted to run with no headers, that would require significant tuning to run properly again. So how Does It run poorly if not tuned differently? Lean. What happens when you run too lean? Burnt exhaust valves. Case and point: high school, Hyundai Elantra GT loaner car, a buddy thought it would be funny to take the header completely off. Although it was so obnoxious it was funny, it not run properly at all. Further, upon return my friend was charged $2400 to replace the head due to burnt exhaust valves.
So, you are right in the sense backpressure is not good for performance, but if it is tuned to be there, it, needs to be there.

Bottom Line- eliminating all backpressure is not beneficial for all engines unless you tune it to accommodate.