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Originally Posted by tw
Periods of minimal exhaust flow followed by a sudden blast out as the exhaust gases of two cylinders exit at the same time. Listen to a vehicle with "tuned headers" - a 1950s technology among car enthusiasts. Tuning results in a sort of smooth buzz. Smooth, even, and quieter. Then listen to an engine without same. It sounds like one loud cylinder among the many farts loudly. Increased noise.
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Yes, tuned headers are designed to keep the exhaust pulses from the indvidual cylinders in an orderly progressive flow. Open headers will produce maximum sound levels and maximum hp. The headers themselves will produce the minimum backpressure the engine needs to run at peak power.
But headers by themselves are not legal because of the noise levels and exhaust must be routed away from the occupants for safety. It's the baffling after the headers, in the exhaust system that control the sound level. If interfering pulses occur they increase the backpressure and reduce flow and power but won't effect or affect the sound level as that's a function of the baffling. The baffling may be designed to give a steady flow or a pulsating flow but it's impossible to design the optimum flow for all operating conditions. It's always a compromise.
Even at a sedate idle of 600 rpm, on a V-8 engine that's 2400 pulses per minute (40 per second) and at a honking 6500 rpm it's 26,000 per minute (433 per second). You're not going to hear an individual cylinder pulse or even paired cylinder pulses. What you hear is the pulses of the exhaust system baffling. If it's uneven it's because the design of the baffling is not suited to the flow of that engine at that rpm.