Wondering around with your intake scoop

Ever wondered what's that extra piping on the OEM intake scoop does? The piping that extends from the throttle body hose and into somewhat kind of canister or container?

The answer is: It's a Helmholtz resonator used to decrease induction noise.


(OEM Intake in a Honda NSX 91')

That empty piece of plastic is called a Helmholtz resonator. Really. And it's just empty. Actually not: It's full of air. It's attached to the ducting between your air cleaner and the intake manifold. And although it looks like it can't have any real purpose, it does. It's there to reduce the noise your engine intake duct makes.

Huh? -- It has an interior volume with a very specific resonant frequency, like an organ pipe. Pressure pulses traveling back and forth in the duct have a resonant frequency as well. A pressure pulse whipping past the entrance to the resonator (at the speed of sound) partially enters its cavity. The pulse then bounces off the far end of the resonator, and returns back to the duct a very short time later.

By now the pressure pulse has traveled a half-wavelength farther along the duct. The pressure pulse re-entering will cancel out at least part of the negative pulse at that point. The net result is reduced noise, at least at or near the resonant frequency of the resonator. Many car manufacturers use this technique to reduce intake-tract noise. Some vehicles have several of these devices in different places along the duct. This device should have no effect whatsoever on the performance of your engine.

So to those looking for stronger induction noise, remove this! It's that simple. Remove it and replace the whole throttle body hose with a stainless or some throttle-hose specific silicone hoses. Get that!