http://www.brighthubengineering.com/...ic-efficiency/

How the Resonator can improve Volumetric Efficiency

In an IC engine, air or the air-fuel mixture is sucked inside the cylinder while the piston is moving toward bottom dead centre (BDC).
As the filling process progresses, the charge air gains more and more momentum, so the speed of the charge air increases gradually.
As soon as the piston reaches BDC, suddenly the inlet valve closes. But, the air in the intake manifold still has a substantial amount of velocity (or dynamic pressure).

Eventually, the flowing charge air hits the closed valve, and the pressure of the charge air at the vicinity of the valve increases. The pressure wave bounces back and starts moving toward the opposite direction.
If a resonator is attached with the inlet manifold, then it will act like a spring to the just-created pressure wave.

The frequency of the resonator determines the speed at which the pressure wave will proceed again toward the inlet valve.

If the frequency of the resonator and the speed of the engine (which determines the interval between the opening and closing of the inlet valve) are properly tuned, the pressure wave will hit the inlet valve again at the time when the inlet valve is open. This phenomenon will cause a rush of charge air into the cylinder. The charge air will be forced into the cylinder, causing the increase in volumetric efficiency.

The point to be noted here is that you will get maximum benefits of increased volumetric efficiency only if the engine running frequency and the resonator frequency are properly tuned. That means you can get maximum benefit only for a particular engine operating speed with a fixed frequency resonator.

For selecting a resonator, the engine operating speed, intake manifold design, and volume of the intake manifold need to be considered. Roughly, the resonator frequency is kept around double the engine frequency in order to get the benefit of the volumetric efficiency increment.

 

Interesting but I'm only left with more questions.

Are the intake resonators on our VQ37 frequency tuned? I left mine on after my CAI install but it seems most people delete them. Are they actually reducing their volumetric efficiency by bypassing them?

 

"you can get maximum benefit only for a particular engine operating speed with a fixed frequency resonator"

does this mean upon acceleration the resonator doesn't work because it's tuned only for a single rpm range or cruising speed (ie 65-75 mph)?

 

RPM, not vehicle speed. It means you can optimize to make more power at one small (not sure how small exactly) window in your RPM band.

 

I understand the theory, but aren't most of the Helmholtz resonators used on cars for the purpose of quieting or tuning the intake sound? The ones on 7AT G37's are attached to the air filter box, although for some reason the 6MT car's don't have them.

Greg

 

You are a true Bill Nye the science guy. Thanks

 

A passive intake has a fixed peak volumetric efficiency with possible harmonics within operation range. However this is why we have VVEL. Ideally it's calibrated to have max volumetric efficiency at all ranges of RPM and load.

How effective the system is in the G is questionable. How adaptive the system is to new intakes is also questionable.

IMO the system is pretty effective by looking at the torque curve for the G. Since the torque curve is fairly flat throughout the RPM ranges it can be coordinated to a somewhat constant volumetric efficiency. Thus meaning the VVEL is doing something. (rather that constant value is near the peak or not is questionable)


Edit: By questionable I mean I don't think many people outside of nissan have the correct data to make an accurate assessment.