I have plenty of experience with engine performance, and s/he was absolutely correct. An overly loud engine is is opening its valves too early or closing too la

I have plenty of experience with engine performance, and s/he was absolutely correct. An overly loud engine is is opening its valves too early or closing too late, and it can only be made quieter by restrictive mufflers. More modern and efficient engine designs, enabled by technologies such as variable valve timing, are quieter out of the valves because they convert more energy into motion instead of sound. Being quieter, they also have less pressure, and are less affected by muffler restrictiveness. Straight pipes might make a 1969 charger more powerful, but the effect on a modern V8 like the BMW N63 is negligible.