Understanding my engine: Pt 1. Detonation
03-11-2006, 02:32 PM
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Understanding my engine: Pt 1. Detonation Ok, so ill prob look stupid here, and im prob in the wrong forum, but asking is the only way ill find out I guess.
Background: Im just getting to spend more time driving after my LT and TD install as spring is springing and the install was late fall.
Scenario: What Ive noticed besides the extreme gassy smell (rich as expected.etc..) is that after a strong 80% ~90% throttle run to whatever speed, letting off the throttle to 10% or 0 to coast and slow down. There will eventualy be a backfire sound coming from the exhaust.
I think its where its coming from, it feels right underneath my *** so thats where I assume it is.
My duals are dumped so it wouldn't be far from me if it was a backfire..i guess.
Question: If this IS detonation, from my understanding of of detonation, it is late or premature combustion due to pressure and heat. (yes/no?)
Would what I'm experiencing if it IS detonation, make sense as there would prob be leftover fuel/gasses in the chambers right after a WOT event, and the cylinders are still higher temp, resulting in the leftover richness detonating?
Does that question make sense?
to try and put it succintly...
I realize im running very rich from the new exhaust and no tune, so the extra fuel in the chambers is detonating after a WOT?
Yeah, thats what I wanna ask... im pretty sure..
Am I understanding whats going on properly or am i way off?
Any input would be appreciated.
Thanks
DJ
Background: Im just getting to spend more time driving after my LT and TD install as spring is springing and the install was late fall.
Scenario: What Ive noticed besides the extreme gassy smell (rich as expected.etc..) is that after a strong 80% ~90% throttle run to whatever speed, letting off the throttle to 10% or 0 to coast and slow down. There will eventualy be a backfire sound coming from the exhaust.
I think its where its coming from, it feels right underneath my *** so thats where I assume it is.
My duals are dumped so it wouldn't be far from me if it was a backfire..i guess.
Question: If this IS detonation, from my understanding of of detonation, it is late or premature combustion due to pressure and heat. (yes/no?)
Would what I'm experiencing if it IS detonation, make sense as there would prob be leftover fuel/gasses in the chambers right after a WOT event, and the cylinders are still higher temp, resulting in the leftover richness detonating?
Does that question make sense?
to try and put it succintly...
I realize im running very rich from the new exhaust and no tune, so the extra fuel in the chambers is detonating after a WOT?
Yeah, thats what I wanna ask... im pretty sure..
Am I understanding whats going on properly or am i way off?
Any input would be appreciated.
Thanks
DJ
03-11-2006, 03:19 PM
#2
Doesn't sound like detonation to me.
What's probably happening is the excess fuel in the pipe/muffler (due to running rich) is being ignited by the heat of the pipe, and it occurs at the lower throttle openings due to the velocity of the exhaust gasses slowing down, allowing the heated pipe to light off the fuel vapor in the exhaust (you may also have a weld standing high in the pipe, and that gets to be a hot spot, that could light it off)
What's probably happening is the excess fuel in the pipe/muffler (due to running rich) is being ignited by the heat of the pipe, and it occurs at the lower throttle openings due to the velocity of the exhaust gasses slowing down, allowing the heated pipe to light off the fuel vapor in the exhaust (you may also have a weld standing high in the pipe, and that gets to be a hot spot, that could light it off)
03-11-2006, 08:50 PM
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Originally Posted by 2K2WS6TA
Doesn't sound like detonation to me.
What's probably happening is the excess fuel in the pipe/muffler (due to running rich) is being ignited by the heat of the pipe, and it occurs at the lower throttle openings due to the velocity of the exhaust gasses slowing down, allowing the heated pipe to light off the fuel vapor in the exhaust (you may also have a weld standing high in the pipe, and that gets to be a hot spot, that could light it off)
What's probably happening is the excess fuel in the pipe/muffler (due to running rich) is being ignited by the heat of the pipe, and it occurs at the lower throttle openings due to the velocity of the exhaust gasses slowing down, allowing the heated pipe to light off the fuel vapor in the exhaust (you may also have a weld standing high in the pipe, and that gets to be a hot spot, that could light it off)
Hopefully soon ill be tuning out the richness and it will help with the problem.
I guess I'd be curious to know what detonation sounds like to make sure I don't have it.
I have noticed some KR in my tuning logs and thought that detonation may be why.
I guess i figured KR meant knock, and knock meant detonation so I figured they were all related.
I'm not sure what you mean by a weld standing high in the pipe? If you mean the welded spots in the system I guess I could understand, i can only think of 2 or 3 places that would be (collectors and the X, everything else is band clamps)
But either way, its good to get info on what could be the causes.
Thanks for the input,
DJ
03-11-2006, 11:09 PM
#4
Detonation can sound like marbles in a can, or it can be a light enough sound that you won't hear it
The KR in your tuning logs does mean the engine is experiencing detonation (knock and detonation are used interchangably BTW) but it may not be loud enough for you to hear.
The weld standing high, it might be that when the guy was welding your system some of the weld came thru and is protruding into the exhaust flow, thus becoming heated, and acting as a hot spot to ignite the excess fuel in the exhaust stream
The bump in the (primative) drawing represents the spot where the weld bead is protruding into the exhaust stream
-------------^------------
The KR in your tuning logs does mean the engine is experiencing detonation (knock and detonation are used interchangably BTW) but it may not be loud enough for you to hear.
The weld standing high, it might be that when the guy was welding your system some of the weld came thru and is protruding into the exhaust flow, thus becoming heated, and acting as a hot spot to ignite the excess fuel in the exhaust stream
The bump in the (primative) drawing represents the spot where the weld bead is protruding into the exhaust stream
-------------^------------
