Theory About Exhaust Drone

[Roger Ramjet]

My experience is that L99 cars are more prone to exhaust induced cabin drone than LS3 cars. I'm thinking the cause might be the radical VVT cam positioning for EGR around 1800 to 2000 RPM. I would test this on my car but I have already done the J-pipe drone killer.

Need a droning car and a tuner to see if the drone can be tuned out. And, if tuned out, does MPG suffer?

[Roger Ramjet]

Here is the area I'm talking about.

[usmc8411]

I have LT's custom x-pipe and muffler delete. I dont have any drone (noticable to me) with AFM turned off. I think people want the best of both worlds and are too picky.

With AFM on it sounds like hot garbage when activated.

[DSteck]

You're probably getting drone from AFM... not the cam timing.

[RickyTheStorm]

Well - here is a note I would definitely like to say because I have been through all of this.

Horrible irritating want to get rid of drone - AFM!!! Without a doubt, I turned it off in my tune and it went away.

Mild low RPM drone - well, I have it on my car even after taking out all of the DoD and replaced to a non VVT cam, etc. A little drone will always be there a low rpm - at least with a flowmaster kit :-)

[Roger Ramjet]

Originally Posted by DSteck

You're probably getting drone from AFM... not the cam timing.

With AFM OFF the drone was still there in top gear, around 1800 RPM, with increasing load (like pulling a hill). I said "was there" because the Helmholtz J-pipe solved the problem. I was thinking maybe there was an easier and cheaper drone solution through VVT tuning.

[DSteck]

It's just physics. Resonance will almost always be there unless there's just lots of sound deadening.

[jbsrace1]

1 7/8 LT headers, High flow cats, X pipe, a pair of 8" cherry bombs replacing the resonator and stock mufflers in the back. AFM set to only work above 55 mph. No drone at all at any speed and sounds great when you jump on it.

I have done this same setup on 3 dif L99's and everyone who drives or hears it loves it.

[mlee]

Originally Posted by DSteck

You're probably getting drone from AFM... not the cam timing.

WADR... AFM noise is not the same thing as Drone nor does it cause drone. The OP has a VVT theory that might be good to play out.

[SonnyakaPig]

Interesting theory, TS. Perhaps we'll learn more about this when more aftermarket VVT cams get intalled in Camaros.

My take on this is that drone can be heard both when AFM is still functioning in the tune and when it is tuned out.

When AFM is still on the car, and you get to about 1700-2000 rpms, the car makes a hollow gargle sound and you can almost feel the car switch to just 4 cylinders. The entire exhaust note changes from how it sounds when all 8 cylinders are firing.

When you cruise with AFM on, the drone in the cabin is a little more pronounced.

Contrast the above with AFM tuned out and the AFM hollow gargle sound disappears and the level of in-cabin drone will depend on the exhaust system installed on your car.

Drone will still be present but it can be drowned out pretty easily with LT's. And even with just a good catback like a Corsa, the drone will be pretty minor.

The drone was most noticable on my car when I had a catback and CAI.

[DSteck]

Originally Posted by mlee

WADR... AFM noise is not the same thing as Drone nor does it cause drone. The OP has a VVT theory that might be good to play out.

AFM is responsible for a vast majority of "exhaust noise" at highway speeds, regardless of what people want to call it (drone or anything else). Turning AFM off will get rid of a lot of the highway speed exhaust noise. As far as tweaking VVT timing, I doubt you're going to adjust the exhaust note anything substantial in terms of decreasing volume/drone. Resonane is resonance... and is a byproduct of the frequency of exhaust pulses. If you want to eliminate drone, the engine has to operate outside of the droning frequency, which is directly related to engine speed. Otherwise, the exhaust needs to be capable of surpressing the resonance by breaking up the sound waves.

[mlee]

Originally Posted by DSteck

AFM is responsible for a vast majority of "exhaust noise" at highway speeds, regardless of what people want to call it (drone or anything else). Turning AFM off will get rid of a lot of the highway speed exhaust noise. As far as tweaking VVT timing, I doubt you're going to adjust the exhaust note anything substantial in terms of decreasing volume/drone. Resonane is resonance... and is a byproduct of the frequency of exhaust pulses. If you want to eliminate drone, the engine has to operate outside of the droning frequency, which is directly related to engine speed. Otherwise, the exhaust needs to be capable of surpressing the resonance by breaking up the sound waves.

Totally agree...

[Roger Ramjet]

I'm thinking drone comes from frequency and amplitude. My Helmholtz pipe is targeted for 120 Hz. Looking at firing pulse frequencies and harmonics, the only RPM that should drone is 2100. My A6 drone started around 1800 - well below 2100.

My idea was to try to decrease the amplitude of the firing pulses by changing VVT cam position. Looking at how far the factory retarded the cam in this RPM range makes me feel advancing the cam is worth a try.

[ArkySS]

I have Flowmaster AMT's and they are loud. The drone was horrible with AFM on. I don't notice it a lick now with it tuned out.