Tech. reason why corvettes backfire
06-19-2017, 12:34 PM
#1
Melting Slicks
Thread Starter
Tech. reason why corvettes backfire
I know they all do I just wanted to know exact reason. Lol
Back my early days if a engine did that, it had timing issue or bad valves.
Thank you
Back my early days if a engine did that, it had timing issue or bad valves.
Thank you
06-19-2017, 01:42 PM
#2
Burning Brakes
Sounds like a backfire to you, but it is not. Doesn't sound like backfires I know of lol.
Copied explanation...The crackling and burbling I think you are refer to is due to the exhaust design. It is the sound of the rapidly condensing exhaust gasses cooling in the exhaust line.
The pipe size of an exhaust exhaust must be optimized for a specific flow rate. This is usually at max RPM and max throttle for high-performance cars. But at idle, the size of the exhaust system is much too large to maintain a constant velocity of the gas for its entire length. This gives you a burbling sound as the exhaust stream has a push-pull effect: some exhaust is pushing out with flow of the engine, some is pulling back as it cools and contracts.
Crackling is the same concept, except more extreme. It happens when you lift the throttle at mid and high RPMs. You have hotter, high velocity exhaust, suddenly followed by cooler, lower velocity gas. The pressure difference between the two crackles while the they equalize. It's a sound that never fails to put a smile on my face!
While the sound and fury is really delightful, it's slightly inefficient because you loose the benefit of the momentum of the exhaust gas which helps escort new exhaust gasses out of the cylinder. This is because the gasses are slowing down as they travel down an exhaust system, burbling and popping and crackling like a boss.
This conflict is solved (and crackling and burbling is eliminated -- boo!) when a control device is placed in the exhaust stream to reduce its size at lower RPMs. A common means is a flapper valve in the muffler. An example on the center two butterfly outlets on a Corvette exhaust.
Copied explanation...The crackling and burbling I think you are refer to is due to the exhaust design. It is the sound of the rapidly condensing exhaust gasses cooling in the exhaust line.
The pipe size of an exhaust exhaust must be optimized for a specific flow rate. This is usually at max RPM and max throttle for high-performance cars. But at idle, the size of the exhaust system is much too large to maintain a constant velocity of the gas for its entire length. This gives you a burbling sound as the exhaust stream has a push-pull effect: some exhaust is pushing out with flow of the engine, some is pulling back as it cools and contracts.
Crackling is the same concept, except more extreme. It happens when you lift the throttle at mid and high RPMs. You have hotter, high velocity exhaust, suddenly followed by cooler, lower velocity gas. The pressure difference between the two crackles while the they equalize. It's a sound that never fails to put a smile on my face!
While the sound and fury is really delightful, it's slightly inefficient because you loose the benefit of the momentum of the exhaust gas which helps escort new exhaust gasses out of the cylinder. This is because the gasses are slowing down as they travel down an exhaust system, burbling and popping and crackling like a boss.
This conflict is solved (and crackling and burbling is eliminated -- boo!) when a control device is placed in the exhaust stream to reduce its size at lower RPMs. A common means is a flapper valve in the muffler. An example on the center two butterfly outlets on a Corvette exhaust.
Last edited by Curt D; 06-19-2017 at 01:43 PM.
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HC Mechanic (06-20-2017)
06-19-2017, 01:49 PM
#3
Melting Slicks
Thread Starter
Sounds like a backfire to you, but it is not. Doesn't sound like backfires I know of lol.
Copied explanation...The crackling and burbling I think you are refer to is due to the exhaust design. It is the sound of the rapidly condensing exhaust gasses cooling in the exhaust line.
The pipe size of an exhaust exhaust must be optimized for a specific flow rate. This is usually at max RPM and max throttle for high-performance cars. But at idle, the size of the exhaust system is much too large to maintain a constant velocity of the gas for its entire length. This gives you a burbling sound as the exhaust stream has a push-pull effect: some exhaust is pushing out with flow of the engine, some is pulling back as it cools and contracts.
Crackling is the same concept, except more extreme. It happens when you lift the throttle at mid and high RPMs. You have hotter, high velocity exhaust, suddenly followed by cooler, lower velocity gas. The pressure difference between the two crackles while the they equalize. It's a sound that never fails to put a smile on my face!
While the sound and fury is really delightful, it's slightly inefficient because you loose the benefit of the momentum of the exhaust gas which helps escort new exhaust gasses out of the cylinder. This is because the gasses are slowing down as they travel down an exhaust system, burbling and popping and crackling like a boss.
This conflict is solved (and crackling and burbling is eliminated -- boo!) when a control device is placed in the exhaust stream to reduce its size at lower RPMs. A common means is a flapper valve in the muffler. An example on the center two butterfly outlets on a Corvette exhaust.
Copied explanation...The crackling and burbling I think you are refer to is due to the exhaust design. It is the sound of the rapidly condensing exhaust gasses cooling in the exhaust line.
The pipe size of an exhaust exhaust must be optimized for a specific flow rate. This is usually at max RPM and max throttle for high-performance cars. But at idle, the size of the exhaust system is much too large to maintain a constant velocity of the gas for its entire length. This gives you a burbling sound as the exhaust stream has a push-pull effect: some exhaust is pushing out with flow of the engine, some is pulling back as it cools and contracts.
Crackling is the same concept, except more extreme. It happens when you lift the throttle at mid and high RPMs. You have hotter, high velocity exhaust, suddenly followed by cooler, lower velocity gas. The pressure difference between the two crackles while the they equalize. It's a sound that never fails to put a smile on my face!
While the sound and fury is really delightful, it's slightly inefficient because you loose the benefit of the momentum of the exhaust gas which helps escort new exhaust gasses out of the cylinder. This is because the gasses are slowing down as they travel down an exhaust system, burbling and popping and crackling like a boss.
This conflict is solved (and crackling and burbling is eliminated -- boo!) when a control device is placed in the exhaust stream to reduce its size at lower RPMs. A common means is a flapper valve in the muffler. An example on the center two butterfly outlets on a Corvette exhaust.
06-19-2017, 02:13 PM
#4
Former Vendor
The popping noise you hear when engine braking is due to DEFCO (deceleration fuel cutoff) more than anything else and you can turn it off if you like in the tune but it is there for fuel economy more than anything.
https://www.hptuners.com/help/vcm_ed...uel_cutoff.htm
https://www.hptuners.com/help/vcm_ed...uel_cutoff.htm
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HC Mechanic (06-20-2017)
06-19-2017, 03:26 PM
#5
Le Mans Master
The popping noise you hear when engine braking is due to DEFCO (deceleration fuel cutoff) more than anything else and you can turn it off if you like in the tune but it is there for fuel economy more than anything.
https://www.hptuners.com/help/vcm_ed...uel_cutoff.htm
https://www.hptuners.com/help/vcm_ed...uel_cutoff.htm
Dave
06-20-2017, 05:22 AM
#6
Burning Brakes
The popping noise you hear when engine braking is due to DEFCO (deceleration fuel cutoff) more than anything else and you can turn it off if you like in the tune but it is there for fuel economy more than anything.
https://www.hptuners.com/help/vcm_ed...uel_cutoff.htm
https://www.hptuners.com/help/vcm_ed...uel_cutoff.htm
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hotrod03 (06-22-2017)
06-20-2017, 06:38 AM
#7
Burning Brakes
DFCO also retards spark which on my setup was the reason for backfire. I saw -5* depending on the RPM and that's where it started to pop. Most people just disable it but I think that makes it worse because it no longer cuts fuel on deceleration but still retards spark to a point ignition occurs close to the exhaust valve opening. A lot of other things also affect this like cam, base spark table, etc...
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hotrod03 (06-22-2017)