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post #1 of 58 (permalink) Old 09-19-2008, 03:45 PM Thread Starter
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Custom exhaust drone fix?

I've read many threads about G8 GT's having drone with custom exhaust. Some even with the Magnaflow's. So the consensus is that the G8 is a PITA with this issue due to the 6 speed auto and AFM. I'm going to give credit to a board member who brought this up some time ago, so if you know who you are say so.

I believe that interior drone is due to that fact that the trunk bottom of the G8's is made up of plastic. Go ahead and knock on it...we might as well call it an amplifier LOL. I'm guessing here but wouldn't applying some sort or sound deadener help resolve this issue? I know of one member that applied dynamat but I don't think he has aftermarket exhaust.

For those who have an issue, would you do this for the common good of the G8 nation? LOL


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post #2 of 58 (permalink) Old 09-19-2008, 03:47 PM Thread Starter
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If I had an aftermarket exhaust, I would do it and tell you guys. It will be a long time before I get one.

Here is the link: Sound Deadening the G8


RIP PONTIAC G8
We were part of the 1st National G8 Meet! (G16)
2008 Pontiac G8 GT (Superchips Cortex, K&N drop-in filter, Corsa catback exhaust)

“In terms of the emotion of it I guess it would be pretty hard to deny the fact that we’re disappointed. The G8 program was a ripper. It was a great car, it was exceptionally well received and it got some fantastic reviews in the States." Mr Whiffin

Last edited by 888GT#31; 09-19-2008 at 03:51 PM.
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post #3 of 58 (permalink) Old 09-19-2008, 03:53 PM
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I might throw some in my tire well shortly, if I do I'll let you know if it works.
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post #4 of 58 (permalink) Old 09-19-2008, 04:30 PM Thread Starter
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Thanks, do tell. I'm hoping this has much to do with the drone.


RIP PONTIAC G8
We were part of the 1st National G8 Meet! (G16)
2008 Pontiac G8 GT (Superchips Cortex, K&N drop-in filter, Corsa catback exhaust)

“In terms of the emotion of it I guess it would be pretty hard to deny the fact that we’re disappointed. The G8 program was a ripper. It was a great car, it was exceptionally well received and it got some fantastic reviews in the States." Mr Whiffin
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post #5 of 58 (permalink) Old 09-19-2008, 05:36 PM
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Yeah, there's good drone....

I replaced the stock muffs with 40 series Flowmasters. The drone that I get with the AFM is a little annoying, but you get used to it. I do plan on putting Dynamat in the trunk to see if it dampens it some. I'll reply when its complete.

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post #6 of 58 (permalink) Old 09-19-2008, 06:06 PM
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Try adding a custom H-pipe.
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post #7 of 58 (permalink) Old 09-19-2008, 06:53 PM
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Quote:
Originally Posted by 888GT#31 View Post
I've read many threads about G8 GT's having drone with custom exhaust. Some even with the Magnaflow's. So the consensus is that the G8 is a PITA with this issue due to the 6 speed auto and AFM. I'm going to give credit to a board member who brought this up some time ago, so if you know who you are say so.

I believe that interior drone is due to that fact that the trunk bottom of the G8's is made up of plastic. Go ahead and knock on it...we might as well call it an amplifier LOL. I'm guessing here but wouldn't applying some sort or sound deadener help resolve this issue? I know of one member that applied dynamat but I don't think he has aftermarket exhaust.

For those who have an issue, would you do this for the common good of the G8 nation? LOL
I would agree that the empty tire well probably makes a nice amplifier.
I am now up and running with the electric cutout sytem attached to the dual exhaust pipes where the take the turn to the sides to hook up with the stock mufflers. With the cutouts closed - stock quiet. Open, we have a straight dual system. The stock resonator was replaced with a SF H-pipe. From there both sides flow back to the cutouts just under the rear axle. Then into glass paks http://www.truckaddons.com/Catalog/s...plehornies.htm that end about 6-8" from the rear bumper. Since room under the G8 is almost non existant, we covered the spare tire well underneath with this: http://www.pegasusautoracing.com/pro...p?Product=1828. The outer shells of the glass paks are less than 1/4" from the reflective sheeting. I then sprayed everything flat black with Hi-Temp header paint to stealth the install. Usually drive the car with cutouts open which routes exhaust straight out thru the glass paks, but also allows some flow thru the stock mufflers. Even with the tire well reflective barrier painted black, the bottom inside the trunk is barely warm after prolonged driving. Result is a very low and nasty rumble at idle and nice note with higher revs. NO DRONE at any speed. You can hear the exhaust in the background at freeway speeds, but I cannot really tell much differance when AFM kicks in.

Since then, I bought a full size spare from G8 Lady and layed it on top of a piece of that convoluted foam they sell for mattresses. Can't really say it's any quieter inside the car but it's not enough to attract the attention of the law enforcement dudes unless I flaunt it. Also had enough of the thermal wrap left over to wrap the New Era CAI. Much less variation in IAT now.
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post #8 of 58 (permalink) Old 09-19-2008, 08:19 PM
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I have the h-pipe and a copy of the magnaflow mufflers. I get the drone in drive while it is coasting down a hill and I think when it goes into dod. I just run mine in the manual mode all the time and it won't do it. I'm guessing that the dod is not active in the manual mode. I did a trip to st louis from the lake and still achieved 21.5 mph, the best I had gotten in drive mode or automatic was 21.9 mpg. That will take care of the drone you are talking about. I might still try the dynomat in the trunk, couldn't hurt.
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post #9 of 58 (permalink) Old 09-20-2008, 07:52 AM
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Quote:
Originally Posted by Screw991le View Post
Try adding a custom H-pipe.
I had an H pipe. It did nothing for the drone of my Magnaflows.
On a trip from Cleveland to Indy, I got 30.1 mpg. A new record for me. 300 miles, and I used 3/8's of a tank of gas.

Your mileage may vary.

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post #10 of 58 (permalink) Old 09-20-2008, 01:54 PM
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Not sure who the member is you are talking about. I talked about the drone also though. It was enough for me to shell out the cash to purchase some corsa db red mufflers. They drone also (tiny bit less) but sound better. I also used dyna mat extreme in the spare wheel well. You were right it's a PITA it still drones! I might try a second coat though as it may have helped a very very small amount. I don't think you can purchase a system at this time that will not drone. If I was in your position I would wait for the Corsa tuned system. It will be your best shot at a system with out / minimal drone. If you can't wait then I would do a custom set up with H pipe and Corsa db blacks. The blacks are loud, if that's not what you want then go red they have a volume just a tad louder than the mf after they break in.
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post #11 of 58 (permalink) Old 09-20-2008, 05:31 PM
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So... having a spare tire is why mine drones less?????

Still wouldn't call it true drone... More like a low hrz vibration due to DOD at certain speeds. I have SF magnaflows, h-pipe, tune and intake insulation delete mod. Have had much worse things than this. Off DOD it's PERFECT.

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post #12 of 58 (permalink) Old 09-20-2008, 07:49 PM
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Has anyone pulled the back seat out? The reason I ask is usually under the bottom portion of the back seat is nothing except frame. You could try dynomatting there as well and I bet it would help some. Just a thought.
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post #13 of 58 (permalink) Old 09-22-2008, 09:55 AM
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Plastic will not carry those frequencies (drone) like metal will. So I don't think that the spare tire well is the problem. I agree that it is more likely to be the other areas where there is no insulation or little insulation.

One big problem will be the size of the exhaust tips. I've learned that the hard way. Looks like the Magnaflow system use 4" tips. If you went with 2 smaller tips (i.e. Borla prototype) then the same system would drone much less.
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post #14 of 58 (permalink) Old 09-22-2008, 11:40 AM
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The only way to eliminate your present drone is to change the exhaust. Add a bullet muffler in-line somewhere in your exhaust (if you must keep your present setup), or change out the current muffler with something different.
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post #15 of 58 (permalink) Old 09-22-2008, 03:07 PM
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My spare tire well is full of moving blankets (they are great for covering the interior) and it still droned like an SOB when AFM kicked in and I had the prototype Corsas installed.

Last edited by 68Rustang; 09-22-2008 at 03:53 PM.
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post #16 of 58 (permalink) Old 09-22-2008, 03:33 PM
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I do think that the plastic spare tire well contributes a lot to the rear suspension thumping noises that make their way into the driving compartment. I don't know about the drone but I have the impression that it's a vibration that is present throughout the length of the exhaust system so the trunk can't be the only culprit.
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post #17 of 58 (permalink) Old 09-22-2008, 04:11 PM
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Drone = resonance at a certain frequency = poor exhaust design, plain and simple.

Your only hope is to fundamentally change your exhaust's frequency by changing (adding or removing) one or more components. If you keep all components the same, you could fill your entire cabin with liquid styrofoam and you would still have a drone.

The easiest thing to do is put a couple of straight-through, perforated mufflers ("bullets") in-line with your present system. Most every muffler manufacturer makes them.

If you don't want to do this, you are faced with yanking your entire system and either buying a new one, or putting the stock one back on.

There is a reason companies put hours and hours into R&D....to work out stuff like this.
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post #18 of 58 (permalink) Old 09-22-2008, 04:14 PM
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Quote:
Drone = resonance at a certain frequency = poor exhaust design, plain and simple.

The easiest thing to do is put a couple of straight-through, perforated mufflers ("bullets") in-line with your present system. Most every muffler manufacturer makes them.

There is a reason companies put hours and hours into R&D....to work out stuff like this.
Well said. And the bullet resonators will typically make the most impact the farther forward they are located.


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post #19 of 58 (permalink) Old 09-22-2008, 04:22 PM
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Quote:
Originally Posted by Mr. Sandog View Post
Drone = resonance at a certain frequency = poor exhaust design, plain and simple.
To add to that, with these cars you are dealing with two separate frequencies. One in V8 mode, and another when AFM kicks into V4 mode. Dialing out one doesn't necessarily dial out the other and getting rid of both might eliminate all the sound you are going for with an aftermarket exhaust in the first place.
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post #20 of 58 (permalink) Old 09-22-2008, 04:56 PM
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Exhaust (cutback) most likely has nothing to do with the drone. From our experience with VE Commodore and now G8, most or the drone which you hear between 1600 to 2000 RPM created at the factory exhaust manifold. The long tubes or Shorty eliminate most of the drone
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