Backfire/pop on decel - Page 2 - Pontiac G8 Forum: G8 Forums - G8Board.com
Exhaust Tech Headers, Catbacks, Mufflers, lack of mufflers

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post #21 of 76 (permalink) Old 04-05-2010, 11:53 AM
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Originally Posted by rez0nance View Post
It's a classic part of V8 exhaust sound - a signature tonal characteristic of a large displacement beast of a beautiful masterpiece of an engine. It absolutely boggles my mind that some people would actually want to get rid of it.
It's nothing more than unburned fuel exploding downstream of the engine. It's so loud in unmuffled racing engines (V8 or otherwise) that it sounds like gunfire.

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post #22 of 76 (permalink) Old 04-05-2010, 12:03 PM
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Hmmm...this gives me an idea. Stay tuned for a poll regarding this

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post #23 of 76 (permalink) Old 04-05-2010, 12:08 PM
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Vote!

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post #24 of 76 (permalink) Old 04-05-2010, 12:15 PM
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I like the sound on 2 door muscle cars. I love the sound on the sedan! When I manually downshift near pedestrians, they always do a double take due the car that is making the sound.

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post #25 of 76 (permalink) Old 04-05-2010, 01:17 PM
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Originally Posted by jmac View Post
This just in....People have different tastes
Well that's fine, but why get a car with a large displacement small block V8 then? The exhaust burble and pops are as much a part of the engine as the cam being in the block. I just don't see how anyone can divorce the two concepts and say "I like small blocks. I hate the small block characteristics."

Just my opinion.

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Originally Posted by RossD View Post
It's nothing more than unburned fuel exploding downstream of the engine. It's so loud in unmuffled racing engines (V8 or otherwise) that it sounds like gunfire.
Oh I know what it is, and I think it's absolutely glorious.

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post #26 of 76 (permalink) Old 04-05-2010, 01:53 PM
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Cars these days are mostly designed to be 'quiet'. I love the fact that our cars buck any 'politically correct' trend!!

No hippie hybrid quietness here!

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post #27 of 76 (permalink) Old 04-05-2010, 02:03 PM
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Cars these days are mostly designed to be 'quiet'. I love the fact that our cars buck any 'politically correct' trend!!

No hippie hybrid quietness here!
Volume isn't whats being discussed.

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post #28 of 76 (permalink) Old 04-05-2010, 02:15 PM
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Quote:
Originally Posted by jmac View Post
Volume isn't whats being discussed.
Based on the post quoted, you are arguing that sound volume is not what is being discussed. IMO, this is incorrect. Since the OP's mods are not causing the sound, this is all about "volume". Once the mufflers were omitted, the sound was no longer muffled, therefore one could say there is an increase in volume or a lack of quietness.

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post #29 of 76 (permalink) Old 04-05-2010, 02:41 PM
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Quote:
Originally Posted by RossD View Post
It's nothing more than unburned fuel exploding downstream of the engine.
The sound is coming from the exhaust not the engine, so I highly doubt that's the case.
The popping is most likely caused when outgoing air & incoming air collide with one another at a certain velocity.
Resonated exhaust tips like Zoomers tend to dramatically reduce this sound, as the tips slow down the reverse vacuum action when one quickly decels.
Particular mufflers tend to quiet that sound as well & these usually tend to be mufflers which don't give an aggressive exhaust note to begin with.

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post #30 of 76 (permalink) Old 04-05-2010, 02:45 PM
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Originally Posted by rez0nance View Post

Oh I know what it is, and I think it's absolutely glorious.
I couldn't agree more!

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post #31 of 76 (permalink) Old 04-05-2010, 02:50 PM
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Originally Posted by El Tejano View Post
The sound is coming from the exhaust not the engine, so I highly doubt that's the case.
The popping is most likely caused when outgoing air & incoming air collide with one another at a certain velocity.
Resonated exhaust tips like Zoomers tend to dramatically reduce this sound, as the tips slow down the reverse vacuum action when one quickly decels.
Particular mufflers tend to quiet that sound as well & these usually tend to be mufflers which don't give an aggressive exhaust note to begin with.
By "downstream," I meant in the exhaust system. Exploding hydrocarbons is an oversimplification, but it explains why I have to clean my exhaust tips all the time!

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post #32 of 76 (permalink) Old 04-05-2010, 02:57 PM
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Quote:
Originally Posted by RossD View Post
By "downstream," I meant in the exhaust system.
Ah yes, you are correct I overlooked that part.

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post #33 of 76 (permalink) Old 04-05-2010, 02:58 PM
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Your just letting the Weaker folks know your there so they can hide their Fords and Mopars!!!

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post #34 of 76 (permalink) Old 04-05-2010, 03:13 PM
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Quote:
Originally Posted by Shredmo View Post
Based on the post quoted, you are arguing that sound volume is not what is being discussed. IMO, this is incorrect. Since the OP's mods are not causing the sound, this is all about "volume". Once the mufflers were omitted, the sound was no longer muffled, therefore one could say there is an increase in volume or a lack of quietness.
Fair enough.

Although, its the increase in volume of the popping thats not desired. The increased volume of the engine is desired, otherwise he wouldn't have put on an aftermarket exhaust to begin with.

I knew within 5 minutes of driving my g8 that the popping would be an issue, for me, with a less muffled exhaust. As posted here: https://www.g8board.com/forums/showthread.php?t=17086 Even with the stock mufflers the cracking, popping, is annoying.

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post #35 of 76 (permalink) Old 04-05-2010, 03:35 PM
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Semantics aside, the G8 is not a luxury car. I feel the abrasive nature of the exhaust sound is part of the car's character. Totally what I expect out of an Australian import. Without it, there is less substance. At the same time, this sound would not be acceptable on a typical Cadillac, Lincoln, Merc, Bimmer or Audi.

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post #36 of 76 (permalink) Old 04-05-2010, 04:04 PM
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Here's another discussion on the subject.

http://www.camaro5.com/forums/showthread.php?p=1369492

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post #37 of 76 (permalink) Old 04-05-2010, 09:55 PM
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Its f^ckin glorious. Nuff' said.

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post #38 of 76 (permalink) Old 04-06-2010, 07:37 AM
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Deacceleration Fuel Cut-Off

The snap-crackle-pop comes from the auto fuel cutoff feature, when you lift off over a certain rev/mph (greater than about 1500 rpm), the fuel will cut off after about 3 seconds and come back on again at around 1000 rpm.

This can be changed in the DFCO setting.
  1. Minimum RPM disable: B2409 - sets the minimum RPM that DFCO can operate. This can be set pretty low but make it over idle PRM and have a bit of over head there.
  2. Minimum RPM Enable: B2410 - over this setting, DFCO can work. Make it over the above setting and allow for some room.
  3. Speed thresholds: B2402 - set to be close on the above settings for each gear.
These should help when DFCO operates and when it doesn't. To alter how quickly it comes into operation...
  • DFCO Entry Delay: B2401 - adjust to your desire. Don't make it come in too quickly though as it may make the car feel like it misses when releasing the throttle. Allow a little longer in low gears and shorter in high gears. Aim for between 1 and 2 seconds as a start.
The above settings will also change how long the crackle lasts when slowing down. If you want it to crackle for longer, add more time.

To change the "note" of the crackle, you need to work on the timing during DFCO entry...

. DFCO Enter Spark Timing: B5149 - lower numbers = more backfires, higher numbers = more burble.

For low backfires and crackle start at maybe a minimum of 0' and remove timing till it sounds "right". Follow the shape of the stock curve.

Hence this can be tuned out or increased to your liking. Note that it is a good feature though as it reduces fuel use.
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post #39 of 76 (permalink) Old 04-06-2010, 08:28 AM
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Aussie,

Amazing details, thanks! I would have never thought that the pop/burble was 'tunable' with an aftermarket exhaust system. Very informative.


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post #40 of 76 (permalink) Old 04-25-2010, 07:09 PM
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Quote:
Originally Posted by cmlease View Post
So, in playing w/ my exhaust (I have kooks long tubes as well as the kooks catted mid pipe) i took off my stock mufflers today. So i'm basically running headers > cats > x-pipe and done. Just wanted to see what it sounded like (thinking of getting the solo axle backs). It sounds good, but there's a lot of backfire/popping going on when i let off the gas. is this normal/is there any danger to this?
The Fuel-Cutoff on Decel can be tuned out if you like but why? It sounds good. There is no danger of any damage to your engine. Enjoy!!!
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