"Exhaust popping" survey
12-11-2002, 02:45 PM
#1
Three Wheelin'
Thread Starter
"Exhaust popping" survey
I have done some searching on Rennlist and also the rest of the internet and found that questions about “popping in exhausts” is a commonly asked question. For those that don’t know this “popping” is typically heard when backing off the throttle/decelerating. The sound comes from fuel igniting in the exhaust or some say just as it exits the exhaust pipe.
Causes may be temporarily rich mixtures due to the delayed response of the fuel computer after the throttle closes and other causes may be air leaks into the exhaust through bad seal rings etc (providing air to support combustion of the un-burnt fuel).
So now I am curious how many of you are experiencing regular exhaust popping and what type of engine/exhaust mods do you have. If you know what your fuel mixtures are like please add that info too.
Mine pops at some point during deceleration on each 20 minute drive. I am still tuning my car after an engine rebuild head work, big turbo, MAP, guru chips, gutted cat, 75 lb injectors. My mixtures are probably close to 12.5 (will confirm after dyno).
Cheers,
OZ951
Causes may be temporarily rich mixtures due to the delayed response of the fuel computer after the throttle closes and other causes may be air leaks into the exhaust through bad seal rings etc (providing air to support combustion of the un-burnt fuel).
So now I am curious how many of you are experiencing regular exhaust popping and what type of engine/exhaust mods do you have. If you know what your fuel mixtures are like please add that info too.
Mine pops at some point during deceleration on each 20 minute drive. I am still tuning my car after an engine rebuild head work, big turbo, MAP, guru chips, gutted cat, 75 lb injectors. My mixtures are probably close to 12.5 (will confirm after dyno).
Cheers,
OZ951
12-11-2002, 03:38 PM
#3
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Mine will pop when coasting in 5th and giving it just enough gas to keep up with the drive wheels but not enough to push it any harder. With my ghetto exhaust it makes it sound like a top fuel dragster at idle... probably not good for it though.
12-11-2002, 03:40 PM
#5
Race Director
Popping???
I have heard popping my race car on decel from WOT high RPM operation.
It had and 87 924S motor stock with straight pipe (no cat or muffler)
I did not notice anthing till I went to the straight pipe (had stock cat and muffler). In my case I think it was always there, but I can hear it much better with the open exhaust.
I think you are right that it has to do with a time lag between the fuel metering and airflow intake.
I have heard popping my race car on decel from WOT high RPM operation.
It had and 87 924S motor stock with straight pipe (no cat or muffler)
I did not notice anthing till I went to the straight pipe (had stock cat and muffler). In my case I think it was always there, but I can hear it much better with the open exhaust.
I think you are right that it has to do with a time lag between the fuel metering and airflow intake.
12-11-2002, 04:53 PM
#6
Three Wheelin'
Thread Starter
Many of the comments that I saw on the net were posted by people who had mods to their exhaust and I expect they tended to be the type of mods that included no catalytic converter.
My popping was pretty regular until I discovered that my idle bypass screw was fully wound in - not surprisingly, winding the idle screw out a turn or two fixed my hot start problem and my hunting idle problem as well as significantly reducing the popping.
My popping was pretty regular until I discovered that my idle bypass screw was fully wound in - not surprisingly, winding the idle screw out a turn or two fixed my hot start problem and my hunting idle problem as well as significantly reducing the popping.
12-11-2002, 04:58 PM
#7
Three Wheelin'
Thread Starter
[quote] Mine will pop when coasting in 5th and giving it just enough gas to keep up with the drive wheels but not enough to push it any harder.<hr></blockquote>
I get a little bit of that as well - when the throttle is only just open a little, I think I will wind back the acceleration enrichment on the Link Box and see how that effects things.
I get a little bit of that as well - when the throttle is only just open a little, I think I will wind back the acceleration enrichment on the Link Box and see how that effects things.
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12-11-2002, 05:14 PM
#8
Unaffiliated
I pop when hot, during shifts, usually between 2nd and third. This mysterious noise seems to coincide with a flame shooting out my cat-less exhaust. At night the mirrors light up letting me know it is there, along with drivers behind me grinning and pointing.. 
<img src="graemlins/beerchug.gif" border="0" alt="[cheers]" />
<img src="graemlins/beerchug.gif" border="0" alt="[cheers]" />
12-11-2002, 05:25 PM
#10
Race Director
[quote]Originally posted by Dan P:
<strong>I pop when hot, during shifts, usually between 2nd and third. This mysterious noise seems to coincide with a flame shooting out my cat-less exhaust. At night the mirrors light up letting me know it is there, along with drivers behind me grinning and pointing..
<img src="graemlins/beerchug.gif" border="0" alt="[cheers]" /> </strong><hr></blockquote>
Mine is almost identical to that scenario except mine does it most on a powerful shift from 1-2 or 2-3. I also pop when decelerating if shes hot, noticed it alot more whenever I run some good leaded race gas in it. Again no cat, stage 2 chips...
<strong>I pop when hot, during shifts, usually between 2nd and third. This mysterious noise seems to coincide with a flame shooting out my cat-less exhaust. At night the mirrors light up letting me know it is there, along with drivers behind me grinning and pointing..
<img src="graemlins/beerchug.gif" border="0" alt="[cheers]" /> </strong><hr></blockquote>
Mine is almost identical to that scenario except mine does it most on a powerful shift from 1-2 or 2-3. I also pop when decelerating if shes hot, noticed it alot more whenever I run some good leaded race gas in it. Again no cat, stage 2 chips...
12-11-2002, 06:38 PM
#12
Race Director
I also remember seeing a 944 Turbo running in PCA F stock (stock engine with stock boost and chips).
He was running with a straight pipe (no cat or muffler)and it was a blast to watch him go down the 5/8 mile drag strip main straight. Each shift resulted in a nice flash of flame out the back of the car that was easily visible during the night enduro.
Really cool!
Of course the two best were a 930 and 964 TurboS at a track day. The 930 was shooting 3ft flames out the back easily visible by day and the 964 TurboS just shot enough soot-up rear bumper. Not sure about 964TurboS but I know the 930 was running very rich and was modded to about 350-400 rwhp
He was running with a straight pipe (no cat or muffler)and it was a blast to watch him go down the 5/8 mile drag strip main straight. Each shift resulted in a nice flash of flame out the back of the car that was easily visible during the night enduro.
Really cool!
Of course the two best were a 930 and 964 TurboS at a track day. The 930 was shooting 3ft flames out the back easily visible by day and the 964 TurboS just shot enough soot-up rear bumper. Not sure about 964TurboS but I know the 930 was running very rich and was modded to about 350-400 rwhp
12-11-2002, 06:51 PM
#13
My 951 pops and gurgles like crazy on deceleration... started when the cat was replaced with a test pipe. Runs just fine, tho... and I love the sound.
Regards, ...Scott
Regards, ...Scott
