Engine/Transmission (1998.5 - 2002) Intake Drone

[Vaughn MacKenzie]

One characteristic of the 24-valve engine is the pronounced intake track drone, more so than 12-valve and common rail engines. For whatever reason it is more noticeable on some 24v trucks than others. Mine wasn't that bad until I installed a VGT turbo, now it's a resonating drone that constantly changes timbre as RPM varies.

I suspect part of it is due to the positioning of the intake horn inlet, maybe where it's located there is more harmonic turbulence in the plenum. That's the only theory I have anyway. Anyone ever try suppressing the noise or am I the only one bothered by it

 

[HookMeUp]

I am bothered by the intake drone also. I believe it is caused by the sharp turn in the intake tube. If you remove the intake tube it is silent. Just haven't had time to pursue this theory yet.

 

[Vaughn MacKenzie]

I have a curved tubular intake horn, the sound didn't change when that was installed. 12-valves have basically the same intake horn but they don't make the same noise.

 

[Alan Reagan]

Hi, Vaughn. Good to see you are still working on these things.



You get drone, when the turbo/engine RPM matches the harmonic resonance of the pipe. I don't think the air flow or bend of the pipe makes it. Diesel engines generate more harmonics that gas engines and the problem is usually more pronounce with a diesel because it can be multiple harmonic frequencies that are causing the drone. Probably in your case you are getting a turbo harmonic almost matching an engine or exhaust harmonic that is causing the problem. I'm not sure if thicker gaskets at the pipe mating surfaces would help attenuate the sound or not (by reducing vibration of the pipe). I have done some sound attenuation using the foam sinusoidal wave material (anechoic foam). There is just no way to get it into the intake system in this situation. If you could stop the vibration in the intake horn, that might do it. But it is probably fairly high frequency and will not go away easily, if at all. If you thought it was all air flow vibration, you could find one of those "Cyclone" things they were selling on TV a few years ago to give smoother air flow throught the system. I think the problem is purely harmonic sounds between the engine, turbo and pipe.



Stupid question, but does the VGT have a silencer ring to at least reduce the high frequency sound at the vanes?

 

[John - K5AWO]

I have a huge air cleaner from a big truck, it has a long corrugated flex hose from the turbo inlet to the cleaner. I hear a little hiss, but not the drone.

 

[RAM1964]

I second that question, does the new vgt have a silencer ring?

 

[dcs1968]

You could always turn up the tunes! :-laf