[some_other_dave]

Originally Posted by ShadeTreeMech

This is better. Variable length intake manifold - Wikipedia, the free encyclopedia

Could something like this be adapted to cars that don't already have it?

It would be challenging to do so, I think. The resonance depends on how much air is being drawn in by the engine, and at what speeds. Getting the right sizes would be a matter of a whole boat-load of computation and then (likely) a bunch of trial and error.

It should be doable, but would likely take any of us (or at least those of us without sizeable amounts of disposable income and/or our own machine shops and plenty of time) quite a long while. And my guess is that the improvements will be relatively small. But that's an almost completely uneducated guess...

-soD