Re: power core iv?
There are a lot of things that go into a good system but my understanding is that you are looking for is a system where the back pressure shuts off the exhaust flow right as the valves close (or piston closes the exhaust port on a two stroke) and then has released all the pressure by the time they reopen. Without back pressure to stop the flow, fuel mixture starts going out the exhaust reducing power and burning stuff up. The more you junk can get out of the cylinder in this short time period the better. This can be done with a quieter system, just not cheaply. When you start getting into more than one cylinder it gets much more complicated because you can start using the flow from one cylinder to suck on another (like a waterbed pump). Thats why on a 4 cylinder bike a 4 into 1 works better then a 4 into 2.