What's the result of a 300 shot w/ TR6's & 26 degrees timing? What about a 200 shot?
#81
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From: Some where in the Corn Fields of Illinois
I assume that is a solid roller? I will take your advice..... swap back to 116 or better gas, use some TR8's, use only 1 kit with a bottle heater and gauges pilled for a 200, and put the timing at 20 degrees. I am running only 11.25:1 compression, so I assume that helps a bit.
Like I said... was fine on the first 10 runs with 116 in it. I am sure dropping it to a 200 and pulling 6 degrees with colder plugs should be safe enough based off our previous findings.... also the IAT's are going to drop with this 60 degree weather now.
Like I said... was fine on the first 10 runs with 116 in it. I am sure dropping it to a 200 and pulling 6 degrees with colder plugs should be safe enough based off our previous findings.... also the IAT's are going to drop with this 60 degree weather now.
I would at least run the TR9's to start with, and definitely run the 116 fuel. These NX plates will make more power than they are jetted for, so tune accordingly. And also, your tune in cooler weather will differ from a tune in warmer weather.
Another saying.... baby steps my friend, baby steps
#82
Yes, a big solid roller. I make peak power on motor at 8100 rpm
I would at least run the TR9's to start with, and definitely run the 116 fuel. These NX plates will make more power than they are jetted for, so tune accordingly. And also, your tune in cooler weather will differ from a tune in warmer weather.
Another saying.... baby steps my friend, baby steps
I would at least run the TR9's to start with, and definitely run the 116 fuel. These NX plates will make more power than they are jetted for, so tune accordingly. And also, your tune in cooler weather will differ from a tune in warmer weather.
Another saying.... baby steps my friend, baby steps
#83
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From: Some where in the Corn Fields of Illinois
This is a street car. He drives it a lot. He would be fine with 110 in the stand alone and pump gas in the tank(especially on a 200). I did it for a long time and never hurt anything. Run a plug in the 8-9 range (there is no "TR8"). And, I would have the tune very conservative for a while. And get a different converter in the car so you dont have to spray so much for the car to run what everybody else does.
Street car or not, he is still making 3XX hp on a 225 hit. That still requires the right fueling and plugs. I know there isn't a "TR8" plug....thats in layman terms so everyone understands it. IMO, he needs more than 110 octane in the standalone for it to be safe. Im not gonna argue because I know what works and is safe. Is a motor worth losing over a few dollars cost difference in fuel or plugs?
#84
Street car or not, he is still making 3XX hp on a 225 hit. That still requires the right fueling and plugs. I know there isn't a "TR8" plug....thats in layman terms so everyone understands it. IMO, he needs more than 110 octane in the standalone for it to be safe. Im not gonna argue because I know what works and is safe. Is a motor worth losing over a few dollars cost difference in fuel or plugs?
And the TR8 comment was directed at Mike. I used to call it that also, and people always fucked with me about it
#85
I had forgot to state earlier that on the last couple 300 hit trips I was in fact running TR6's, and 16* of timing 109 octane leaded, with a 11.25:1 comp. So yes the TR6s can survive, but I will be changing to a colder plug as I move up a tad in shot size, and a little more timing pull. How often are you big sprayers changing out your plug? I think Brad stated once, IIRC, that he changes each pass?
Robert
Robert
#87
I had forgot to state earlier that on the last couple 300 hit trips I was in fact running TR6's, and 16* of timing 109 octane leaded, with a 11.25:1 comp. So yes the TR6s can survive, but I will be changing to a colder plug as I move up a tad in shot size, and a little more timing pull. How often are you big sprayers changing out your plug? I think Brad stated once, IIRC, that he changes each pass?
Robert
Robert
I changed my plugs every 5-6 times I went out. Dont really think it needed it I just did it lol. At 1st I checked them after every pass. Once I knew it was dialed in I checked them every night when I got home(or the next day).
#88
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From: Some where in the Corn Fields of Illinois
Who made 3xx on a 225 hit Its not worth arguing over. It will be fine on either 110 or 116. If 116 makes you sleep better at night then go for it. I ran 110 on a 200-250 shot for almost a year and raced probably 3-4 nights a week street and track and never had a problem with the 110 in the stand alone(which he bought from me).
And the TR8 comment was directed at Mike. I used to call it that also, and people always fucked with me about it
And the TR8 comment was directed at Mike. I used to call it that also, and people always fucked with me about it
I think the hp numbers came from someone in PM that I was helping
On my car with the high compression (almost 15:1), I use VP Nitrous fuel (120 Octane). I talked to several big nitrous companies and for what I was doing they recomended it. Better to be safe than sorry with a $20K engine
Another post above mentioned the 11.1 AFR and lower thing... most NX kits that my tuner has used has made the most power and ran the best at around 10.6-10.8 AFR. He does what works, and we leave it at that
#89
First off, I didn't tune the car, so I had no Idea the timing was at 26, as a rule of thumb you retard 1 to 1 1/2 degress for every 50hp of nitrous. Mikes car made max power with between 30-32 dgs if I remember correctly, so the timing was retarded and no problems were detected on the dyno or the track. I personally pulled the plugs after Mike had used 2 bottles and they looked great. As far as the TR6's being in his car, yes that was my bad because we couldn't find them in time for him to race jeremy, I then forgot about them being in there, after all Mike is not our only customer and I can not keep up with what everyone has. I do know they were gapped at .028 and his car was setup for 116 octane. The whole problem is lack of getting the right equipment, lack of pateince, and misunderstandings. I am planning on going to Mikes house and doing a leak down on it one day this week to save him on towing it to the shop.
#90
IMO plugs are secondary to timing and octane. You can get away with a much hotter plug with alot of octane and alot of timing retard. Obviously all three play a part. But I have run TR6 many mnay times on a 300+ shot in a pinch...but I always made sure I had a bit more octane to cover the detonation resistance.
Play it safe with all three (timing, heat range and octane) But I put heat range of plugs just behind timing and octane in order of importance. Thats assuming your atleast CLOSE on heat range. Obviously at some point a VERY hot plug will cause detonation or preignition regardless of octane and timing. Same can be said of the other two parameters as well.
Play it safe with all three (timing, heat range and octane) But I put heat range of plugs just behind timing and octane in order of importance. Thats assuming your atleast CLOSE on heat range. Obviously at some point a VERY hot plug will cause detonation or preignition regardless of octane and timing. Same can be said of the other two parameters as well.
#91
I had forgot to state earlier that on the last couple 300 hit trips I was in fact running TR6's, and 16* of timing 109 octane leaded, with a 11.25:1 comp. So yes the TR6s can survive, but I will be changing to a colder plug as I move up a tad in shot size, and a little more timing pull. How often are you big sprayers changing out your plug? I think Brad stated once, IIRC, that he changes each pass?
Robert
Robert
I have 500 pills in mine right now and it makes a solid 365 to the tires and I wouldn't ever even think about a TR6 but if people want to run their expensive *** LS1 engines on the ragged edge then so be it.
12 degrees total timing,116 N2O specific fuel (Sunoco), and 10s = 950 to the tires.
#92
I change my plugs every pass or 2. I pull them out every pass and check them so I can make adjustments in the tune to try and make distribution even better. YOU CAN NOT RUN THESE PLUGS BACK TO THE PITS AFTER THE PASS AND GET A READING OFF OF THEM. Must shut the car off and pull it back around. I run 10s in my motor.
I can't tell you how many times I have seen the a/f ratio off the chart rich. We used to run the black car (5.56@125 in the 1/8) with 10.0:1 or fatter. I have heard of big blocks doing that though. My buddy has a 632 that was to fat and lifted some rings up. So far to date I have never seen a LS1 to fat....LOL....If you watch my videos that are in this section, my car black smokes the entire way down the track which you would think is to rich but the wideband and EGTs say different. Plugs look good on each pass.
That doesn't mean you were safe. If you ask any big nitrous person, he would say you were crazy....Doesn't matter if it will work if it is not the right way. Every motor reacts differently. You can see both signs (timing and heat range) on plugs when you pull them out. Heat range is on the threads and I bet yours didn't even show any burn on the threads. LOL
I have 500 pills in mine right now and it makes a solid 365 to the tires and I wouldn't ever even think about a TR6 but if people want to run their expensive *** LS1 engines on the ragged edge then so be it.
12 degrees total timing,116 N2O specific fuel (Sunoco), and 10s = 950 to the tires.
I can't tell you how many times I have seen the a/f ratio off the chart rich. We used to run the black car (5.56@125 in the 1/8) with 10.0:1 or fatter. I have heard of big blocks doing that though. My buddy has a 632 that was to fat and lifted some rings up. So far to date I have never seen a LS1 to fat....LOL....If you watch my videos that are in this section, my car black smokes the entire way down the track which you would think is to rich but the wideband and EGTs say different. Plugs look good on each pass.
That doesn't mean you were safe. If you ask any big nitrous person, he would say you were crazy....Doesn't matter if it will work if it is not the right way. Every motor reacts differently. You can see both signs (timing and heat range) on plugs when you pull them out. Heat range is on the threads and I bet yours didn't even show any burn on the threads. LOL
I have 500 pills in mine right now and it makes a solid 365 to the tires and I wouldn't ever even think about a TR6 but if people want to run their expensive *** LS1 engines on the ragged edge then so be it.
12 degrees total timing,116 N2O specific fuel (Sunoco), and 10s = 950 to the tires.
plugs looked fine the car still runs today over a year later. with that timing the car only put down 470 rwhp haha, and with the 400 hit it made 420 more to the tires. One way or another we are talking about tuning, its a total combination of timing, fuel and plug heat range like 383LQ4 had said.
#93
plugs looked fine the car still runs today over a year later. with that timing the car only put down 470 rwhp haha, and with the 400 hit it made 420 more to the tires. One way or another we are talking about tuning, its a total combination of timing, fuel and plug heat range like 383LQ4 had said.
#94
I'll look in to it next time I get it on my dyno I just put on a new solid roller top end package on there, so it should be able to ingest the nitrous really well hehe.
#95
I can't tell you how many times I have seen the a/f ratio off the chart rich. We used to run the black car (5.56@125 in the 1/8) with 10.0:1 or fatter. I have heard of big blocks doing that though. My buddy has a 632 that was to fat and lifted some rings up. So far to date I have never seen a LS1 to fat....LOL....If you watch my videos that are in this section, my car black smokes the entire way down the track which you would think is to rich but the wideband and EGTs say different. Plugs look good on each pass.
thanks for the input much appriciated
thanks for the input much appriciated
#96
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Detonation
Unburned end gas, under increasing pressure and heat (from the normal progressive burning process and hot combustion chamber metals) spontaneously combusts, ignited solely by the intense heat and pressure. The remaining fuel in the end gas simply lacks sufficient octane rating to withstand this combination of heat and pressure.
Detonation causes a very high, very sharp pressure spike in the combustion chamber but it is of a very short duration. If you look at a pressure trace of the combustion chamber process, you would see the normal burn as a normal pressure rise, then all of a sudden you would see a very sharp spike when the detonation occurred. That spike always occurs after the spark plug fires. The sharp spike in pressure creates a force in the combustion chamber. It causes the structure of the engine to ring, or resonate, much as if it were hit by a hammer. Resonance, which is characteristic of combustion detonation, occurs at about 6400 Hertz. So the pinging you hear is actually the structure of the engine reacting to the pressure spikes. This noise of detonation is commonly called spark knock. This noise changes only slightly between iron and aluminum. This noise or vibration is what a knock sensor picks up. The knock sensors are tuned to 6400 hertz and they will pick up that spark knock. Incidentally, the knocking or pinging sound is not the result of "two flame fronts meeting" as is often stated. Although this clash does generate a spike the noise you sense comes from the vibration of the engine structure reacting to the pressure spike.
One thing to understand is that detonation is not necessarily destructive. Many engines run under light levels of detonation, even moderate levels. Some engines can sustain very long periods of heavy detonation without incurring any damage. If you've driven a car that has a lot of spark advance on the freeway, you'll hear it pinging. It can run that way for thousands and thousands of miles. It's not an optimum situation but it is not a guaranteed instant failure. The higher the specific output (HP/in3) of the engine, the greater the sensitivity to detonation. An engine that is making 0.5 HP/in3 or less can sustain moderate levels of detonation without any damage; but an engine that is making 1.5 HP/in3, if it detonates, it will probably be damaged fairly quickly, here I mean within minutes.
Detonation causes three types of failure:
1. Mechanical damage (broken ring lands, rod bearing failure)
2. Abrasion (pitting of the piston crown)
3. Overheating (scuffed piston skirts due to excess heat input or high coolant temperatures)
The high impact nature of the spike can cause fractures; it can break the spark plug electrodes, the porcelain around the plug, cause a clean fracture of the ring land and can actually cause fracture of valves-intake or exhaust. The piston ring land, either top or second depending on the piston design, is susceptible to fracture type failures. If I were to look at a piston with a second broken ring land, my immediate suspicion would be detonation.
Another thing detonation can cause is a sandblasted appearance to the top of the piston. The piston near the perimeter will typically have that kind of look if detonation occurs. It is a swiss-cheesy look on a microscopic basis. The detonation, the mechanical pounding, actually mechanically erodes or fatigues material out of the piston. You can typically expect to see that sanded look in the part of the chamber most distant from the spark plug, because if you think about it, you would ignite the flame front at the plug, it would travel across the chamber before it got to the farthest reaches of the chamber where the end gas spontaneously combusted. That's where you will see the effects of the detonation. You might see it at the hottest part of the chamber in some engines, possibly by the exhaust valves. In that case the end gas was heated to detonation by the residual heat in the valve.
In a four valve engine with a pent roof chamber with a spark plug in the center, the chamber is fairly uniform in distance around the spark plug. But one may still may see detonation by the exhaust valves because that area is usually the hottest part of the chamber. Where the end gas is going to be hottest is where the damage, if any, will occur.
Because this pressure spike is very severe and of very short duration, it can actually shock the boundary layer of gas that surrounds the piston. Combustion temperatures exceed 1800 degrees. If you subjected an aluminum piston to that temperature, it would just melt. The reason it doesn't melt is because of thermal inertia and because there is a boundary layer of a few molecules thick next to the piston top. This thin layer isolates the flame and causes it to be quenched as the flame approaches this relatively cold material. That combination of actions normally protects the piston and chamber from absorbing that much heat. However, under extreme conditions the shock wave from the detonation spike can cause that boundary layer to breakdown which then lets a lot of heat transfer into those surfaces.
Engines that are detonating will tend to overheat, because the boundary layer of gas gets interrupted against the cylinder head and heat gets transferred from the combustion chamber into the cylinder head and into the coolant. So it starts to overheat. The more it overheats, the hotter the engine, the hotter the end gas, the more it wants to detonate, the more it wants to overheat. It's a snowball effect. That's why an overheating engine wants to detonate and that's why engine detonation tends to cause overheating.
Many times you will see a piston that is scuffed at the "four corners". If you look at the bottom side of a piston you see the piston pin boss. If you look across each pin boss it's solid aluminum with no flexibility. It expands directly into the cylinder wall. However, the skirt of a piston is relatively flexible. If it gets hot, it can deflect. The crown of the piston is actually slightly smaller in diameter on purpose so it doesn't contact the cylinder walls. So if the piston soaks up a lot of heat, because of detonation for instance, the piston expands and drives the piston structure into the cylinder wall causing it to scuff in four places directly across each boss. It's another dead giveaway sign of detonation. Many times detonation damage is just limited to this.
Some engines, such as air cooled 2-stroke engines found in snowmobiles, watercraft and motorcycles, have a very common detonation failure mode. What typically happens is that when detonation occurs the piston expands excessively, scuffs in the bore along those four spots and wipes material into the ring grooves. The rings seize so that they can't conform to the cylinder walls. Engine compression is lost and the engine either stops running, or you start getting blow-by past the rings that torches out an area, then the engine quits.
In the shop someone looks at the melted result and says, "pre-ignition damage". No, it's detonation damage. Detonation caused the piston to scuff and this snowballed into loss of compression and hot gas escaping by the rings that caused the melting. Once again, detonation is a source of confusion and it is very difficult, sometimes, to pin down what happened, but in terms of damage caused by detonation, this is another typical sign.
While some of these examples may seem rather tedious I mention them because a "scuffed piston" is often blamed on other factors and detonation as the problem is overlooked. A scuffed piston may be an indicator of a much more serious problem which may manifest itself the next time with more serious results.
In the same vein, an engine running at full throttle may be happy due to a rich WOT air/fuel ratio. Throttling back to part throttle the mixture may be leaner and detonation may now occur. Bingo, the piston overheats and scuffs, the engine fails but the postmortem doesn't consider detonation because the the failure didn't happen at WOT.
I want to reinforce the fact that the detonation pressure spike is very brief and that it occurs after the spark plug normally fires. In most cases that will be well after ATDC, when the piston is moving down. You have high pressure in the chamber anyway with the burn. The pressure is pushing the piston like it's supposed to, and superimposed on that you get a brief spike that rings the engine.
Unburned end gas, under increasing pressure and heat (from the normal progressive burning process and hot combustion chamber metals) spontaneously combusts, ignited solely by the intense heat and pressure. The remaining fuel in the end gas simply lacks sufficient octane rating to withstand this combination of heat and pressure.
Detonation causes a very high, very sharp pressure spike in the combustion chamber but it is of a very short duration. If you look at a pressure trace of the combustion chamber process, you would see the normal burn as a normal pressure rise, then all of a sudden you would see a very sharp spike when the detonation occurred. That spike always occurs after the spark plug fires. The sharp spike in pressure creates a force in the combustion chamber. It causes the structure of the engine to ring, or resonate, much as if it were hit by a hammer. Resonance, which is characteristic of combustion detonation, occurs at about 6400 Hertz. So the pinging you hear is actually the structure of the engine reacting to the pressure spikes. This noise of detonation is commonly called spark knock. This noise changes only slightly between iron and aluminum. This noise or vibration is what a knock sensor picks up. The knock sensors are tuned to 6400 hertz and they will pick up that spark knock. Incidentally, the knocking or pinging sound is not the result of "two flame fronts meeting" as is often stated. Although this clash does generate a spike the noise you sense comes from the vibration of the engine structure reacting to the pressure spike.
One thing to understand is that detonation is not necessarily destructive. Many engines run under light levels of detonation, even moderate levels. Some engines can sustain very long periods of heavy detonation without incurring any damage. If you've driven a car that has a lot of spark advance on the freeway, you'll hear it pinging. It can run that way for thousands and thousands of miles. It's not an optimum situation but it is not a guaranteed instant failure. The higher the specific output (HP/in3) of the engine, the greater the sensitivity to detonation. An engine that is making 0.5 HP/in3 or less can sustain moderate levels of detonation without any damage; but an engine that is making 1.5 HP/in3, if it detonates, it will probably be damaged fairly quickly, here I mean within minutes.
Detonation causes three types of failure:
1. Mechanical damage (broken ring lands, rod bearing failure)
2. Abrasion (pitting of the piston crown)
3. Overheating (scuffed piston skirts due to excess heat input or high coolant temperatures)
The high impact nature of the spike can cause fractures; it can break the spark plug electrodes, the porcelain around the plug, cause a clean fracture of the ring land and can actually cause fracture of valves-intake or exhaust. The piston ring land, either top or second depending on the piston design, is susceptible to fracture type failures. If I were to look at a piston with a second broken ring land, my immediate suspicion would be detonation.
Another thing detonation can cause is a sandblasted appearance to the top of the piston. The piston near the perimeter will typically have that kind of look if detonation occurs. It is a swiss-cheesy look on a microscopic basis. The detonation, the mechanical pounding, actually mechanically erodes or fatigues material out of the piston. You can typically expect to see that sanded look in the part of the chamber most distant from the spark plug, because if you think about it, you would ignite the flame front at the plug, it would travel across the chamber before it got to the farthest reaches of the chamber where the end gas spontaneously combusted. That's where you will see the effects of the detonation. You might see it at the hottest part of the chamber in some engines, possibly by the exhaust valves. In that case the end gas was heated to detonation by the residual heat in the valve.
In a four valve engine with a pent roof chamber with a spark plug in the center, the chamber is fairly uniform in distance around the spark plug. But one may still may see detonation by the exhaust valves because that area is usually the hottest part of the chamber. Where the end gas is going to be hottest is where the damage, if any, will occur.
Because this pressure spike is very severe and of very short duration, it can actually shock the boundary layer of gas that surrounds the piston. Combustion temperatures exceed 1800 degrees. If you subjected an aluminum piston to that temperature, it would just melt. The reason it doesn't melt is because of thermal inertia and because there is a boundary layer of a few molecules thick next to the piston top. This thin layer isolates the flame and causes it to be quenched as the flame approaches this relatively cold material. That combination of actions normally protects the piston and chamber from absorbing that much heat. However, under extreme conditions the shock wave from the detonation spike can cause that boundary layer to breakdown which then lets a lot of heat transfer into those surfaces.
Engines that are detonating will tend to overheat, because the boundary layer of gas gets interrupted against the cylinder head and heat gets transferred from the combustion chamber into the cylinder head and into the coolant. So it starts to overheat. The more it overheats, the hotter the engine, the hotter the end gas, the more it wants to detonate, the more it wants to overheat. It's a snowball effect. That's why an overheating engine wants to detonate and that's why engine detonation tends to cause overheating.
Many times you will see a piston that is scuffed at the "four corners". If you look at the bottom side of a piston you see the piston pin boss. If you look across each pin boss it's solid aluminum with no flexibility. It expands directly into the cylinder wall. However, the skirt of a piston is relatively flexible. If it gets hot, it can deflect. The crown of the piston is actually slightly smaller in diameter on purpose so it doesn't contact the cylinder walls. So if the piston soaks up a lot of heat, because of detonation for instance, the piston expands and drives the piston structure into the cylinder wall causing it to scuff in four places directly across each boss. It's another dead giveaway sign of detonation. Many times detonation damage is just limited to this.
Some engines, such as air cooled 2-stroke engines found in snowmobiles, watercraft and motorcycles, have a very common detonation failure mode. What typically happens is that when detonation occurs the piston expands excessively, scuffs in the bore along those four spots and wipes material into the ring grooves. The rings seize so that they can't conform to the cylinder walls. Engine compression is lost and the engine either stops running, or you start getting blow-by past the rings that torches out an area, then the engine quits.
In the shop someone looks at the melted result and says, "pre-ignition damage". No, it's detonation damage. Detonation caused the piston to scuff and this snowballed into loss of compression and hot gas escaping by the rings that caused the melting. Once again, detonation is a source of confusion and it is very difficult, sometimes, to pin down what happened, but in terms of damage caused by detonation, this is another typical sign.
While some of these examples may seem rather tedious I mention them because a "scuffed piston" is often blamed on other factors and detonation as the problem is overlooked. A scuffed piston may be an indicator of a much more serious problem which may manifest itself the next time with more serious results.
In the same vein, an engine running at full throttle may be happy due to a rich WOT air/fuel ratio. Throttling back to part throttle the mixture may be leaner and detonation may now occur. Bingo, the piston overheats and scuffs, the engine fails but the postmortem doesn't consider detonation because the the failure didn't happen at WOT.
I want to reinforce the fact that the detonation pressure spike is very brief and that it occurs after the spark plug normally fires. In most cases that will be well after ATDC, when the piston is moving down. You have high pressure in the chamber anyway with the burn. The pressure is pushing the piston like it's supposed to, and superimposed on that you get a brief spike that rings the engine.
#100
Originally Posted by J-Rod
Detonation
Unburned end gas, under increasing pressure and heat (from the normal progressive burning process and hot combustion chamber metals) spontaneously combusts, ignited solely by the intense heat and pressure. The remaining fuel in the end gas simply lacks sufficient octane rating to withstand this combination of heat and pressure.
Detonation causes a very high, very sharp pressure spike in the combustion chamber but it is of a very short duration. If you look at a pressure trace of the combustion chamber process, you would see the normal burn as a normal pressure rise, then all of a sudden you would see a very sharp spike when the detonation occurred. That spike always occurs after the spark plug fires. The sharp spike in pressure creates a force in the combustion chamber. It causes the structure of the engine to ring, or resonate, much as if it were hit by a hammer. Resonance, which is characteristic of combustion detonation, occurs at about 6400 Hertz. So the pinging you hear is actually the structure of the engine reacting to the pressure spikes. This noise of detonation is commonly called spark knock. This noise changes only slightly between iron and aluminum. This noise or vibration is what a knock sensor picks up. The knock sensors are tuned to 6400 hertz and they will pick up that spark knock. Incidentally, the knocking or pinging sound is not the result of "two flame fronts meeting" as is often stated. Although this clash does generate a spike the noise you sense comes from the vibration of the engine structure reacting to the pressure spike.
One thing to understand is that detonation is not necessarily destructive. Many engines run under light levels of detonation, even moderate levels. Some engines can sustain very long periods of heavy detonation without incurring any damage. If you've driven a car that has a lot of spark advance on the freeway, you'll hear it pinging. It can run that way for thousands and thousands of miles. It's not an optimum situation but it is not a guaranteed instant failure. The higher the specific output (HP/in3) of the engine, the greater the sensitivity to detonation. An engine that is making 0.5 HP/in3 or less can sustain moderate levels of detonation without any damage; but an engine that is making 1.5 HP/in3, if it detonates, it will probably be damaged fairly quickly, here I mean within minutes.
Detonation causes three types of failure:
1. Mechanical damage (broken ring lands, rod bearing failure)
2. Abrasion (pitting of the piston crown)
3. Overheating (scuffed piston skirts due to excess heat input or high coolant temperatures)
The high impact nature of the spike can cause fractures; it can break the spark plug electrodes, the porcelain around the plug, cause a clean fracture of the ring land and can actually cause fracture of valves-intake or exhaust. The piston ring land, either top or second depending on the piston design, is susceptible to fracture type failures. If I were to look at a piston with a second broken ring land, my immediate suspicion would be detonation.
Another thing detonation can cause is a sandblasted appearance to the top of the piston. The piston near the perimeter will typically have that kind of look if detonation occurs. It is a swiss-cheesy look on a microscopic basis. The detonation, the mechanical pounding, actually mechanically erodes or fatigues material out of the piston. You can typically expect to see that sanded look in the part of the chamber most distant from the spark plug, because if you think about it, you would ignite the flame front at the plug, it would travel across the chamber before it got to the farthest reaches of the chamber where the end gas spontaneously combusted. That's where you will see the effects of the detonation. You might see it at the hottest part of the chamber in some engines, possibly by the exhaust valves. In that case the end gas was heated to detonation by the residual heat in the valve.
In a four valve engine with a pent roof chamber with a spark plug in the center, the chamber is fairly uniform in distance around the spark plug. But one may still may see detonation by the exhaust valves because that area is usually the hottest part of the chamber. Where the end gas is going to be hottest is where the damage, if any, will occur.
Because this pressure spike is very severe and of very short duration, it can actually shock the boundary layer of gas that surrounds the piston. Combustion temperatures exceed 1800 degrees. If you subjected an aluminum piston to that temperature, it would just melt. The reason it doesn't melt is because of thermal inertia and because there is a boundary layer of a few molecules thick next to the piston top. This thin layer isolates the flame and causes it to be quenched as the flame approaches this relatively cold material. That combination of actions normally protects the piston and chamber from absorbing that much heat. However, under extreme conditions the shock wave from the detonation spike can cause that boundary layer to breakdown which then lets a lot of heat transfer into those surfaces.
Engines that are detonating will tend to overheat, because the boundary layer of gas gets interrupted against the cylinder head and heat gets transferred from the combustion chamber into the cylinder head and into the coolant. So it starts to overheat. The more it overheats, the hotter the engine, the hotter the end gas, the more it wants to detonate, the more it wants to overheat. It's a snowball effect. That's why an overheating engine wants to detonate and that's why engine detonation tends to cause overheating.
Many times you will see a piston that is scuffed at the "four corners". If you look at the bottom side of a piston you see the piston pin boss. If you look across each pin boss it's solid aluminum with no flexibility. It expands directly into the cylinder wall. However, the skirt of a piston is relatively flexible. If it gets hot, it can deflect. The crown of the piston is actually slightly smaller in diameter on purpose so it doesn't contact the cylinder walls. So if the piston soaks up a lot of heat, because of detonation for instance, the piston expands and drives the piston structure into the cylinder wall causing it to scuff in four places directly across each boss. It's another dead giveaway sign of detonation. Many times detonation damage is just limited to this.
Some engines, such as air cooled 2-stroke engines found in snowmobiles, watercraft and motorcycles, have a very common detonation failure mode. What typically happens is that when detonation occurs the piston expands excessively, scuffs in the bore along those four spots and wipes material into the ring grooves. The rings seize so that they can't conform to the cylinder walls. Engine compression is lost and the engine either stops running, or you start getting blow-by past the rings that torches out an area, then the engine quits.
In the shop someone looks at the melted result and says, "pre-ignition damage". No, it's detonation damage. Detonation caused the piston to scuff and this snowballed into loss of compression and hot gas escaping by the rings that caused the melting. Once again, detonation is a source of confusion and it is very difficult, sometimes, to pin down what happened, but in terms of damage caused by detonation, this is another typical sign.
While some of these examples may seem rather tedious I mention them because a "scuffed piston" is often blamed on other factors and detonation as the problem is overlooked. A scuffed piston may be an indicator of a much more serious problem which may manifest itself the next time with more serious results.
In the same vein, an engine running at full throttle may be happy due to a rich WOT air/fuel ratio. Throttling back to part throttle the mixture may be leaner and detonation may now occur. Bingo, the piston overheats and scuffs, the engine fails but the postmortem doesn't consider detonation because the the failure didn't happen at WOT.
I want to reinforce the fact that the detonation pressure spike is very brief and that it occurs after the spark plug normally fires. In most cases that will be well after ATDC, when the piston is moving down. You have high pressure in the chamber anyway with the burn. The pressure is pushing the piston like it's supposed to, and superimposed on that you get a brief spike that rings the engine.
Detonation
Unburned end gas, under increasing pressure and heat (from the normal progressive burning process and hot combustion chamber metals) spontaneously combusts, ignited solely by the intense heat and pressure. The remaining fuel in the end gas simply lacks sufficient octane rating to withstand this combination of heat and pressure.
Detonation causes a very high, very sharp pressure spike in the combustion chamber but it is of a very short duration. If you look at a pressure trace of the combustion chamber process, you would see the normal burn as a normal pressure rise, then all of a sudden you would see a very sharp spike when the detonation occurred. That spike always occurs after the spark plug fires. The sharp spike in pressure creates a force in the combustion chamber. It causes the structure of the engine to ring, or resonate, much as if it were hit by a hammer. Resonance, which is characteristic of combustion detonation, occurs at about 6400 Hertz. So the pinging you hear is actually the structure of the engine reacting to the pressure spikes. This noise of detonation is commonly called spark knock. This noise changes only slightly between iron and aluminum. This noise or vibration is what a knock sensor picks up. The knock sensors are tuned to 6400 hertz and they will pick up that spark knock. Incidentally, the knocking or pinging sound is not the result of "two flame fronts meeting" as is often stated. Although this clash does generate a spike the noise you sense comes from the vibration of the engine structure reacting to the pressure spike.
One thing to understand is that detonation is not necessarily destructive. Many engines run under light levels of detonation, even moderate levels. Some engines can sustain very long periods of heavy detonation without incurring any damage. If you've driven a car that has a lot of spark advance on the freeway, you'll hear it pinging. It can run that way for thousands and thousands of miles. It's not an optimum situation but it is not a guaranteed instant failure. The higher the specific output (HP/in3) of the engine, the greater the sensitivity to detonation. An engine that is making 0.5 HP/in3 or less can sustain moderate levels of detonation without any damage; but an engine that is making 1.5 HP/in3, if it detonates, it will probably be damaged fairly quickly, here I mean within minutes.
Detonation causes three types of failure:
1. Mechanical damage (broken ring lands, rod bearing failure)
2. Abrasion (pitting of the piston crown)
3. Overheating (scuffed piston skirts due to excess heat input or high coolant temperatures)
The high impact nature of the spike can cause fractures; it can break the spark plug electrodes, the porcelain around the plug, cause a clean fracture of the ring land and can actually cause fracture of valves-intake or exhaust. The piston ring land, either top or second depending on the piston design, is susceptible to fracture type failures. If I were to look at a piston with a second broken ring land, my immediate suspicion would be detonation.
Another thing detonation can cause is a sandblasted appearance to the top of the piston. The piston near the perimeter will typically have that kind of look if detonation occurs. It is a swiss-cheesy look on a microscopic basis. The detonation, the mechanical pounding, actually mechanically erodes or fatigues material out of the piston. You can typically expect to see that sanded look in the part of the chamber most distant from the spark plug, because if you think about it, you would ignite the flame front at the plug, it would travel across the chamber before it got to the farthest reaches of the chamber where the end gas spontaneously combusted. That's where you will see the effects of the detonation. You might see it at the hottest part of the chamber in some engines, possibly by the exhaust valves. In that case the end gas was heated to detonation by the residual heat in the valve.
In a four valve engine with a pent roof chamber with a spark plug in the center, the chamber is fairly uniform in distance around the spark plug. But one may still may see detonation by the exhaust valves because that area is usually the hottest part of the chamber. Where the end gas is going to be hottest is where the damage, if any, will occur.
Because this pressure spike is very severe and of very short duration, it can actually shock the boundary layer of gas that surrounds the piston. Combustion temperatures exceed 1800 degrees. If you subjected an aluminum piston to that temperature, it would just melt. The reason it doesn't melt is because of thermal inertia and because there is a boundary layer of a few molecules thick next to the piston top. This thin layer isolates the flame and causes it to be quenched as the flame approaches this relatively cold material. That combination of actions normally protects the piston and chamber from absorbing that much heat. However, under extreme conditions the shock wave from the detonation spike can cause that boundary layer to breakdown which then lets a lot of heat transfer into those surfaces.
Engines that are detonating will tend to overheat, because the boundary layer of gas gets interrupted against the cylinder head and heat gets transferred from the combustion chamber into the cylinder head and into the coolant. So it starts to overheat. The more it overheats, the hotter the engine, the hotter the end gas, the more it wants to detonate, the more it wants to overheat. It's a snowball effect. That's why an overheating engine wants to detonate and that's why engine detonation tends to cause overheating.
Many times you will see a piston that is scuffed at the "four corners". If you look at the bottom side of a piston you see the piston pin boss. If you look across each pin boss it's solid aluminum with no flexibility. It expands directly into the cylinder wall. However, the skirt of a piston is relatively flexible. If it gets hot, it can deflect. The crown of the piston is actually slightly smaller in diameter on purpose so it doesn't contact the cylinder walls. So if the piston soaks up a lot of heat, because of detonation for instance, the piston expands and drives the piston structure into the cylinder wall causing it to scuff in four places directly across each boss. It's another dead giveaway sign of detonation. Many times detonation damage is just limited to this.
Some engines, such as air cooled 2-stroke engines found in snowmobiles, watercraft and motorcycles, have a very common detonation failure mode. What typically happens is that when detonation occurs the piston expands excessively, scuffs in the bore along those four spots and wipes material into the ring grooves. The rings seize so that they can't conform to the cylinder walls. Engine compression is lost and the engine either stops running, or you start getting blow-by past the rings that torches out an area, then the engine quits.
In the shop someone looks at the melted result and says, "pre-ignition damage". No, it's detonation damage. Detonation caused the piston to scuff and this snowballed into loss of compression and hot gas escaping by the rings that caused the melting. Once again, detonation is a source of confusion and it is very difficult, sometimes, to pin down what happened, but in terms of damage caused by detonation, this is another typical sign.
While some of these examples may seem rather tedious I mention them because a "scuffed piston" is often blamed on other factors and detonation as the problem is overlooked. A scuffed piston may be an indicator of a much more serious problem which may manifest itself the next time with more serious results.
In the same vein, an engine running at full throttle may be happy due to a rich WOT air/fuel ratio. Throttling back to part throttle the mixture may be leaner and detonation may now occur. Bingo, the piston overheats and scuffs, the engine fails but the postmortem doesn't consider detonation because the the failure didn't happen at WOT.
I want to reinforce the fact that the detonation pressure spike is very brief and that it occurs after the spark plug normally fires. In most cases that will be well after ATDC, when the piston is moving down. You have high pressure in the chamber anyway with the burn. The pressure is pushing the piston like it's supposed to, and superimposed on that you get a brief spike that rings the engine.
Robert