[johnunit]

In a modern EFI engine, I really don't see how narrowing/restricting anything other than the individual runners to each cylinder will increase efficiency. Even then, that's very dependent on gearing, load, runner length, how well tuned the CSA (Cross Sectional Area) was to begin with, etc.

Anything on the outside of the throttle, and especially on the outside/before the MAF is just increasing pumping losses.

I think a lot of these theories are ones that are valid with old-tech single plenum inlines or high-duration and CSA V8s, etc. They don't translate to modern engines that are much better tuned for cruising speed operation and have far better mixture, emulsion, swirl, etc.