Exhaust Drone

Discussion on fuel delivery & intake/exhaust tech & mods.
leadfart
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Joined: Wed Mar 20, 2013 12:00 am
Location: Treasure Island, Lake McQueeney, TX

Re: Exhaust Drone

Post by leadfart »

I vote for de-activate AFM. Did you really buy this car for its fuel economy? No daggers, please! :lol: There are plenty of options, when you delete AFM. The OEM mufflers and OEM piping, do an excellent job of eliminating drone and AFM.

If you want pleasing sounds, AFM has to go! :mrgreen:
Bob Dannelley
2011 Alto Gray 9C3 Caprice PPV-Maggie-11.64@119.68-Sold!
1995 DCM Impala SS-409-Stroker!-11.83@115
2014 Silver Ice LTZ Silverado Crewcab 4X4
2007 Black Z51 M6-Corvette Coupe
ImpalaPPV
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Location: Arizona

Re: Exhaust Drone

Post by ImpalaPPV »

Getting rid of AFM is an easy option but its does not "solve" the drone issue technically. I don't own a Caprice (yet) but with the amount of driving I do I'd probably leave the AFM alone. I just want to know how to set up an exhaust that eliminates drone...but sounds decent. This is really more of a puzzle for me to just toy around with. But since I plan on buying a Caprice as my next car I may as well solve a useful puzzle.
Navy Lifer
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Re: Exhaust Drone

Post by Navy Lifer »

here's what I can offer:

The L99 Camaro has flapper valves (called an "adaptive exhaust valve") in the mid-pipe as part of the AFM drone "fix" - I had a line on an L99 system that had been removed to scavenge them and try them on the PPV, and I'm still not ruling out such an approach, just to see IF it works. They do not seem to be available separately, at least from GM. I also do not assume that they are a universal fit item--the spring and flapper over-center position may be critical to proper performance on a given vehicle, based on engine size, piping size, exhaust mass flow between 8 & 4 cylinder modes, and many other factors.

thread on Camaro 5 on the adaptive exhaust valve:
http://www.camaro5.com/forums/showthread.php?t=146353" onclick="window.open(this.href);return false;

one post of particular note:
http://www.camaro5.com/forums/showpost. ... stcount=15" onclick="window.open(this.href);return false;

The Dynomax VT may work to mitigate drone, but I've seen more complaints than good reports regarding the flapper mechanism being noisy - "clanking" for want of a better description.

The SS sedan exhaust is "different" compared to PPV, as a whole system. While the engines are part of that (an added 60 HP and greater mass flow has to be dealt with), the stock SS system has a very nice "sporty" sound profile under throttle--realize there is no AFM mode, so the muffler is a more open design, internally.

Putting the SS sedan mufflers on the PPV does make for a nice sound under heavy throttle, but it is still significantly toned-down, compared the sound of the same mufflers on the SS, when using the rest of the stock PPV system, so it's clear that the "center muffler" assembly is a significant part of the overall design approach difference taken for PPV vs SS. In AFM mode, the difference is significant, and it isn't pleasant. Short of doing away with AFM, my approach was to look for the flapper valves from the Camaro to give that a try.

CORSA "claims" no drone on G8 GT (with AFM)--I don't know whether the CORSA system offers any real improvement in flow or power output--or potential to handle power upgrades compared to a stock system, but I'll assume it offers a more pleasing "performance" tone, and it is far "prettier" than the stock system, as are most aftermarket systems.

While I tend to agree with Bob's latest comment, it's clear there are some things that could be tried (flapper valves) and there are aftermarket products that claim to deal with the AFM/drone issue (CORSA, Solo) that would provide a more aggressive exhaust tone than stock, whether AFM is active or not--which remains to be validated or disproved. Solo system owners can comment on this, as there are at least a few using that setup, as an axle-back setup.
leadfart
Posts: 465
Joined: Wed Mar 20, 2013 12:00 am
Location: Treasure Island, Lake McQueeney, TX

Re: Exhaust Drone

Post by leadfart »

I still have credits left on my HPtuners, I'd tune yours out for free, Bill. Of course, you have to come see me! :mrgreen:
Bob Dannelley
2011 Alto Gray 9C3 Caprice PPV-Maggie-11.64@119.68-Sold!
1995 DCM Impala SS-409-Stroker!-11.83@115
2014 Silver Ice LTZ Silverado Crewcab 4X4
2007 Black Z51 M6-Corvette Coupe
leadfart
Posts: 465
Joined: Wed Mar 20, 2013 12:00 am
Location: Treasure Island, Lake McQueeney, TX

Re: Exhaust Drone

Post by leadfart »

My Christmas present to me, a converter, coming soon! 8-)
Bob Dannelley
2011 Alto Gray 9C3 Caprice PPV-Maggie-11.64@119.68-Sold!
1995 DCM Impala SS-409-Stroker!-11.83@115
2014 Silver Ice LTZ Silverado Crewcab 4X4
2007 Black Z51 M6-Corvette Coupe
User avatar
GTObert
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Location: Jordan, MN

Re: Exhaust Drone

Post by GTObert »

leadfart wrote:I vote for de-activate AFM. Did you really buy this car for its fuel economy? No daggers, please! :lol: There are plenty of options, when you delete AFM. The OEM mufflers and OEM piping, do an excellent job of eliminating drone and AFM.

If you want pleasing sounds, AFM has to go! :mrgreen:
This is pretty much sums up my thoughts on the AFM. I started this thread to talk about the resonance caused by having headers and large exhaust tubing, not to talk about the problems involved in the ridiculousness of turning off half your cylinders. Honestly, I have not seen my mileage go down since deactivating the system and I don't see the advantage of keeping it.

That being said, if you wanted to try a 1/4 wave resonance pipe to try and eliminate this particular drone then you certainly could. The math is fairly simple to come up with a length. Here's a great explanation of how to calculate it.

http://www.performancetrucks.net/forums ... ne-489463/" onclick="window.open(this.href);return false;

So it depends on what RPM you are at when you get the drone. Let's just say 1750 RPM which is 70 mph in 6th gear. The frequency for 8 cylinders is 116.67 Hz, making the wavelength 2.94 meters. Divide the wavelength by 4 and you have the length of your pipe, .735 meters. In 4 cylinder mode, you would cut the frequency in half (58.33 Hz). This results in a 1.47 meter tube length, exactly double the first length.

If, for some unknown reason, you wanted to keep your AFM active after installing aftermarket exhaust and have a resonator to eliminate drone in both 4 and 8 cylinder mode, you could simply make the long version of the pipe and weld a washer with a center hole half the diameter of the pipe exactly in the center. (Does this make sense to anyone?) With a washer in the middle of your pipe half the soundwaves will reflect back at the shorter wavelength and half at the longer wavelength, eliminating both.
2011 9C1
2005 GTO
SuperDutyDave
Posts: 52
Joined: Fri Aug 08, 2014 5:23 pm
Location: People's Republic of Vermont

Re: Exhaust Drone

Post by SuperDutyDave »

I added rotofab intake and solo axle back exhaust along with dyno tuning including AFM delete.

Car runs and sounds great......no drone whatsoever and fuel mileage seems no worse for wear
Dave AKA "SuperDuty"

2013 9C1 Caprice PPV

2015 Chevrolet Silverado 2500-HD 4X4 ext-cab

2009 Deere 5525 4WD Full Cab Tractor

2010 Harley Davidaon Road Glide

Tax Payer Paid Chevy Pickup and 400 HP Patrol Boat
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