Exactly. Many people make the mistake of thinking of an exhaust system as equivalent to a hose, but it's not. In a hose the flow is constant and a bigger hose will simply allow ore flow. In an exhaust, a pressure wave of hot, high pressure gas is sent down the pipe every time an exhaust valve opens and then closes. It's not about flow, but velocity. Not higher velocity or lower velocity, but the most appropriate velocity for your intended rpm range of the engine. Behind this pulse naturally comes an area of low-pressure. Inevitably the high pressure "ball" reaches a place in the system that alters it's velocity (a widening or narrowing section of pipe, a muffler, a crossover, etc.). Depending on the design of the system when the high and low pressure areas collide at this "junction" it will create a stronger or weaker pressure wave that travels back and hits the back of the exhaust valve. The timing of this pressure wave can either interfere with evacuation of the combustion chamber, or aid it. It it it hits when the exhaust valve is opening, it will cause a bit of backwash into the combustion chamber. However, it can also aid evacuation of the combustion chamber if it creates a low pressure zone at the moment the exhaust valve opens (scavenging).
Then the witch doctor comes out and waving his panther tooth necklace, tells you the right place to put tour x-pipe and what size pipe to use for optimum performance at a certain rpm.
All of that said, it is widely accepted that for pipes of equal design, a smaller pipe will give you better low rpm performance and a larger pipe is better for high rpm. Higher rpm = more volume of exhaust gases, thus flow is certainly an issue here, but I'm thinking, perhaps erroneously, that part of the issue is that the big, slow moving pulses in a larger pipe are carrying a larger volume of gases in their pressure wave and are just overwhelming the exhaust port at low rpms, causing poor scavenging at low rpms and thus the whole "big pipes are bad for low end power" phenomenon. That's just my theory and I have more studying to do.
Anyhow, it is certainly true that larger pipes are louder and boomier and more likely to drone and drive you insane at 2500 rpm when you are cruising down the freeway.
Then the witch doctor comes out and waving his panther tooth necklace, tells you the right place to put tour x-pipe and what size pipe to use for optimum performance at a certain rpm.
All of that said, it is widely accepted that for pipes of equal design, a smaller pipe will give you better low rpm performance and a larger pipe is better for high rpm. Higher rpm = more volume of exhaust gases, thus flow is certainly an issue here, but I'm thinking, perhaps erroneously, that part of the issue is that the big, slow moving pulses in a larger pipe are carrying a larger volume of gases in their pressure wave and are just overwhelming the exhaust port at low rpms, causing poor scavenging at low rpms and thus the whole "big pipes are bad for low end power" phenomenon. That's just my theory and I have more studying to do.
Anyhow, it is certainly true that larger pipes are louder and boomier and more likely to drone and drive you insane at 2500 rpm when you are cruising down the freeway.
