First of all the link you had to the post was a vender trying to sell. They don't have any Flows on their site so im sure they will put them down as much as possible.

Last time I checked backpressure helped torque and hurt top end HP. Yet everybody says the lose torque because the flowmaster baffles/chambers, and the baffles and chambers are what create the little backpressure needed. Some people seem to have it backwords. It can't have backpressure and cause torque loss.

If you want loud though, don't even look at magnaflow unless its a race muffler, or a magnaflow magpak. Or you can just not use mufflers.

 

Where "outside the combustion chamber" is this supposedly helpful vacuum created? If it's downstream of the exhaust it sure can't help charge the cylinder, because the valve is closed. And since it is the inertia of the air that helps maximize charging the cylinder with air (due to it's speed rushing into the cylinder) backpressure while the valve is in the process of closing would slow down the speed of the incoming air, and hurt that air charging process. My understanding is you want the lowest backpressure possible at all times, to flow as much fresh air into the cylinder and scavenge all possible exhaust gases. Tuned exhaust counts on the low-pressure pulse reducing the backpressure even further, helping pull maximum flow through the cylinder. Those low-pressure pulses are from an "echo" from the exhaust tip or bouncing back from a major diameter change or another cylinder.

Any link or documented basis for your claim? I definitely would be interested, because I've never heard a credible "backpressure is good" concept and I can't picture the mechanics of it working.