Just one of those crazy ideas you have at random moments...

The big drawback of big port engines is overlap, correct? Well why not install some type of engine run vacuum leading to the exhaust ports that creates very low pressure at the port and when it opens sucks the exhaust out and puts it into exhaust system.

It would stop pumping losses and help with overlap.

Why would this/wouldn't this work? Just asking. Who knows?

-Falken

 

The exhaust system already does this. The slug of exhaust gases leaving the port has a lot of inertia associated with it (that's why it's so loud) and it pulls the rest of the exhaust out with it and can (and does) create a vacuum in the exhaust system all on its own.

That is why a too large exhaust on a N/A will kill power, the exhaust slows down too much and this inertia is lost, and the rotor ends up having to physically push the gases out. (Turbos are a different kettle of fish since most of the inertia is lost in driving the turbine)

 

That would be a heck of a big vacuum required to suck out the exhaust.

 

I always assumed the reverse pulse was something weak that only helped "a little".

 

It's not necessarily due to wave harmonics, just the fact that high energy gases (hot/high pressure/high velocity) act a lot like a liquid. The effect is always there even when the harmonics are hurting you rather than helping. (If you want proof, you'd see the engine's VE following the different harmonic orders rather closely. In practice this doesn't happen)

PS - You know those big Roots blowers that are used sometimes on V8s, the 6-71/8-71/14-71 jobs? Those were originally designed to be the scavenge blowers on GMC 2-stroke Diesels...