Originally Posted by M3PO
High velocities are more important near the cylinders where high velocity help scavenging by creating low pressure that "sucks" the exhaust out of the cylinder. This also creates unwanted back pressure because pressure loss in a pipe is a function of velocity. Near the muffler, high exhaust velocity isn't as important. In fact, the exhaust cools quite a bit and slows down (because it's volume is reduced when it cools) back there. Near the muffler, you simply want to reduce pressure loss/back pressure. Reducing the amount of bends and velocity (larger pipes) are both ways to reduce back pressure. The gases do slow down but there isn't "a wall", there is less restriction.
Most of this is true but does not explain why you want gas that is already at its slowest point due to being cool, near the end, want to make it even slower and not efficiently exit the system as a smaller pipe (or atleast the same size as the rest of the exhaust) would do. If the whole thing was 3 inches then fine but 2.5 and than 3 at the end. Taking slow gases there and making them even less able to exit with slower velocity due to piping, being cool and being at the end of the system so has lost a lot of kinetic energy.
I was just looking for a reason which I don't think is unreasonable when people way 2k for an exhaust. Have we really gotten to the point we defend tuning companies just because of their name without a sensible explanation?
Its lacking those standards which allow companies to just sell products that lack any real quality or testing (not saying AA does this) but clearly you guys realize this happens all the time with unsubstantiated claims and people buying a crap load of products.
Was real simple, I don't doubt its a great AA system but can someone tell me an explanation that uses physics and makes sense to go from a smaller pipe throughout to a larger pipe at the end