Why cold start is so loud if valves are closed

[Lual]

Hi, why the sound is so loud at start up if the valves are closed?

Furthermore, why once the car has warmed up a bit, you cannot reproduce the sound by revving Up?

I am just curious as in many threads, it is said that the way to increase sound seems to be wiring up the valves.

Thanks

[F30form]

Valve overlap is increased quite a bit on start up in order to heat up the catalytic converters as quickly as possible. This is done for emissions reasons. As soon as this initial period is over, the overlap returns to normal and the volume is decreased.

*Ninja edit, by valve overlap I am referring to the valves in the head, not the exhaust valves.

[greentrbo95gst]

love the ninja edit

[johntomferg]

*ninjistics*