Mike, it's interesting stuff, all right...

You've got exhaust being released under very high pressure. This makes a big bang, just like a gunshot.

that bang is still resonating when the intake valve opens, although the pressure is in the chamber is now low or even below atmospheric (depending on rpm). A sonic shockwave goes out the intake, through the open throttle, and out the horn into open air -- again just like an unterminated waveguide.

This causes an opposing pulse to reflect back in the opposite direction, back down the intake. You can calculate the length of the intake so that round trip at the speed of sound pressurizes the intake charge at the rpm of your choice, the longer the length, the lower the rpm.

Varies a bit with air density as that changes the speed of sound, but the concept works.