ELI5-Why does your car lose power when you cut the exhaust
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Exhaust isn’t a constant velocity flow – each time the exhaust valves open, high pressure exhaust enters the pipe, then there is a brief period of pressure drop until the next valve opens, making the pressure over time cyclical.
As new exhaust enters the pipe, it pushes against existing gases in the pipe, creating pressure which moves all the exhaust out. If the gases are moving quickly, there will be lower pressure at the exhaust valves, allowing for the next release of exhaust to enter the pipe more easily. If you were to replace your exhaust pipe with wider pipe, the exhaust would have a state of lower pressure with a resulting lower velocity. This means the last pressure wave of exhaust doesn’t move as far down the pipe when the next is released, creating higher pressure at the latter end of the valves and leading to the engine needing to work a bit harder to evacuate the cylinders.
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