Not just racing engines, but that’s a very well known design item. Lots of people were surprised when Mercedes showed up with a log exhaust for 2014.gruntguru wrote: ↑04 Sep 2021, 09:38There is also the phenomenon of exhaust tuning (pulses are much stronger in the exhaust runners due to the high cylinder pressure at EVO). Race engine manifolds are tuned so that a strong negative pressure wave arrives at the exhaust valve just before it closes. This pulls the last bit of exhaust out of the cylinder at TDC and sends a negative wave out the intake valve (which is also open at TDC). This is the main driver of waves in the intake manifold.Hoffman900 wrote: ↑03 Sep 2021, 23:47. . . . The pressure waves in the intake port / manifold does not occur due to the air column "slamming into the back of the valve"... the origins for that, that I can find are in Superflow's manual and repeated adnaseum by magazines. If the air slams into the back of the valve, you closed it too soon .
It originates at valve open due to the shock of the pressure differential, between the port and cylinder as the piston starts to descend and creates a depression. . . .
Exhaust tuning is also the main reason why for performance V8’s, a flat plane is preferred over a (in the US more common) cross plane. BMW has a form of variable exhausts on their production superbike since 2010, with valves in the balance pipes.