Festival of Speed at Cal Speedway /Auto Club Speedway April 20 2018 - 928s running?
07-27-2018 | 10:29 AM
#316
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From: MA
An interesting document that confirms my suspicions as I read it. Pre-ignition is an uncontrolled burn that I associate with overheating and ultimately burning holes in pistons. As pistons overheat their yield stress and UTS will drop rapidly beyond a certain temperature point. Once certain boundary conditions have been met it does not take a lot of imagination to understand how a super knock event can destroy an engine even if it were a single occurrence type of thing. That there is such a thing as "Super Knock" and it has an accepted name tells us something. That it has the characteristics that it does tells us something else. The failure that has occurred does fit the conventional failure profile associated with pre-ignition [holed pistons] or conventional detonation [ring damage etc]. In any failure investigation one has to come up with credible scenarios that can explain the damage seen. Can you think of anything else that might explain the damage described? As I can understand Super Knock is a catastrophic event.
Now look at the motor itself- how many 928 engines have been built with this spec? Indeed how many has Greg built? I would not be at all surprised if this motor was a one of a kind build. Based on what Greg has written it has a compression ratio in excess of 12 to 1 and was specifically designed to run 110 octane race gas [not ethanol] and runs 32 degrees of advance. Gasoline blending streams with this octane are few and far between and such octane probably cannot be achieved without the use of TEL [or so I suspect]. User experience of such a motor must be very limited and I would not mind betting this particular motor has relatively few run hours to its name given the nature of the beast. Consequently experience running such a motor must be very limited. That Mark A was running the motor and seemingly not fully aware of the need for 110 octane was most unfortunate. Even if there was a perception that `100 octane was required I would want to know that what I had in the tank was RON 100 and that I had credible provenance to know such was in there. Mixing up a bucket of this and a bucket of that is just not credible to my way of thinking- the best that can be said is that such approach might get you in the right ball park but no better than that.
So, if this event was not a result of "Super knock" what other phenomena could have cracked the pistons in the manner described? For sure I do no know of any.
Now look at the motor itself- how many 928 engines have been built with this spec? Indeed how many has Greg built? I would not be at all surprised if this motor was a one of a kind build. Based on what Greg has written it has a compression ratio in excess of 12 to 1 and was specifically designed to run 110 octane race gas [not ethanol] and runs 32 degrees of advance. Gasoline blending streams with this octane are few and far between and such octane probably cannot be achieved without the use of TEL [or so I suspect]. User experience of such a motor must be very limited and I would not mind betting this particular motor has relatively few run hours to its name given the nature of the beast. Consequently experience running such a motor must be very limited. That Mark A was running the motor and seemingly not fully aware of the need for 110 octane was most unfortunate. Even if there was a perception that `100 octane was required I would want to know that what I had in the tank was RON 100 and that I had credible provenance to know such was in there. Mixing up a bucket of this and a bucket of that is just not credible to my way of thinking- the best that can be said is that such approach might get you in the right ball park but no better than that.
So, if this event was not a result of "Super knock" what other phenomena could have cracked the pistons in the manner described? For sure I do no know of any.
If irregular combustion caused the piston overheating, I don't believe that it could have been just spark knock. The reason for this is that spark knock doesn't lower the EGTs and all the piston tests I know of say that spark knock, even severe, doesn't cause meaningful overheating of the piston. For the piston to overheat because of irregular combustion keeping the quantity of air and fuel constant, one must observe lower EGTs and that basically only happens with pre-ignition. Because of this reason, I think that pre-ignition is the one plausible reason how irregular combustion could have caused the piston overheating.
In a highly tuned engine, pre-ignition often causes severe knock within the same cycle, as pressure and temperature of the unburned charge rises. This often registers as super knock or mega knock. The super knock or mega knock can by my understanding only overheat the piston if it's associated with pre-ignition, however. Furthermore, pre-ignition induced knock is not controllable by retarding ignition. Only completely safe way to stop preignition is cutting off fuel, closing the throttle, and/or opening the wastegate.
So then the question is what caused the pre-ignition. Measuring the fuel octane from the tank would be one interesting thing. Carefully examining the spark plugs for heat range and for insulation damage would be another thing.
07-27-2018 | 11:24 AM
#317
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From: Oman
The piston crown cracks are caused by overheating. If it's pressure, the cracks usually appear at the pin boss, not on the crown. It's the temperature gradient that causes the crack on the crown. From that, and the fact that the piston underside is black from burned oil, I'd say it's highly likely that the piston overheated. Given the other damage, I'd also say that it's highly likely that there was some kind of irregular combustion. What is not as clear is whether the piston overheated first before irregular combustion or the irregular combustion caused the piston overheating. My guess is latter, but it's a guess.
If irregular combustion caused the piston overheating, I don't believe that it could have been just spark knock. The reason for this is that spark knock doesn't lower the EGTs and all the piston tests I know of say that spark knock, even severe, doesn't cause meaningful overheating of the piston. For the piston to overheat because of irregular combustion keeping the quantity of air and fuel constant, one must observe lower EGTs and that basically only happens with pre-ignition. Because of this reason, I think that pre-ignition is the one plausible reason how irregular combustion could have caused the piston overheating.
In a highly tuned engine, pre-ignition often causes severe knock within the same cycle, as pressure and temperature of the unburned charge rises. This often registers as super knock or mega knock. The super knock or mega knock can by my understanding only overheat the piston if it's associated with pre-ignition, however. Furthermore, pre-ignition induced knock is not controllable by retarding ignition. Only completely safe way to stop preignition is cutting off fuel, closing the throttle, and/or opening the wastegate.
So then the question is what caused the pre-ignition. Measuring the fuel octane from the tank would be one interesting thing. Carefully examining the spark plugs for heat range and for insulation damage would be another thing.
If irregular combustion caused the piston overheating, I don't believe that it could have been just spark knock. The reason for this is that spark knock doesn't lower the EGTs and all the piston tests I know of say that spark knock, even severe, doesn't cause meaningful overheating of the piston. For the piston to overheat because of irregular combustion keeping the quantity of air and fuel constant, one must observe lower EGTs and that basically only happens with pre-ignition. Because of this reason, I think that pre-ignition is the one plausible reason how irregular combustion could have caused the piston overheating.
In a highly tuned engine, pre-ignition often causes severe knock within the same cycle, as pressure and temperature of the unburned charge rises. This often registers as super knock or mega knock. The super knock or mega knock can by my understanding only overheat the piston if it's associated with pre-ignition, however. Furthermore, pre-ignition induced knock is not controllable by retarding ignition. Only completely safe way to stop preignition is cutting off fuel, closing the throttle, and/or opening the wastegate.
So then the question is what caused the pre-ignition. Measuring the fuel octane from the tank would be one interesting thing. Carefully examining the spark plugs for heat range and for insulation damage would be another thing.
The yield strength of aluminium alloy drops off markedly with heat, 40ksi at ambient, about 2.7ksi at 315C. Q. What temperature does lube oil coke at? A.- around 315C. The temperature weakens the metal, the pressure cracks it. I have seen pre-ignition melt pistons but not crack them- thus why the "Super Knock" concept intrigues me. Something had to hammer the pistons to do that damage or so my decrepit brain tells me.
07-27-2018 | 12:04 PM
#318
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From: MA
From what I can piece together the likely sequence of events is low octane fuel [100 instead of 110] is the root cause, overheating due to pre-ignition taking place cooks the oil on the underside of the pistons, Super knock event[s] subsequently take place to finish the motor off. As I can understand a Super knock event can only take place if a pre-ignition condition exists- correct? I have previously stated for the benefit of those trying to follow why the knock control system is no use in a pre-ignition condition albeit it should be patently obvious why. The yield strength of aluminium alloy drops off markedly with heat, 40ksi at ambient, about 2.7ksi at 315C. Q. What temperature does lube oil coke at? A.- around 315C. The temperature weakens the metal, the pressure cracks it. I have seen pre-ignition melt pistons but not crack them- thus why the "Super Knock" concept intrigues me. Something had to hammer the pistons to do that damage or so my decrepit brain tells me.
07-27-2018 | 12:06 PM
#319
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From: Anaheim
Clarification information:
The cracks on the domes of the pistons are continuations of the cracks at the base of the pin bosses on the underside.
On some of the pistons, it is difficult to figure out what is keeping the entire pin boss structure attached to the rest of the piston.
The dome of the completely failed piston/rod actually has "divots" above the what is left of the piston bosses.
Because of the extent of the damage and the fact that every piston is broken, I have a tough time imagining one "super knock" being responsible.
The cracks on the domes of the pistons are continuations of the cracks at the base of the pin bosses on the underside.
On some of the pistons, it is difficult to figure out what is keeping the entire pin boss structure attached to the rest of the piston.
The dome of the completely failed piston/rod actually has "divots" above the what is left of the piston bosses.
Because of the extent of the damage and the fact that every piston is broken, I have a tough time imagining one "super knock" being responsible.
07-27-2018 | 12:15 PM
#320
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From: MA
many modern STREET engines run VERY high compression on our crap 91 octane...my little miata is 13-1 and runs just great on 91, but I'm not racing it.... My old M3 was 12-1 on 91 and spun to 8400rpm....again STREET engines.... Another very possible issue is 928's run very old (think slow) ECU...yes they were state of the art, but not anymore. Those of us that remember our very 1st PC in the mid to late 80's....how fast were they? Sure the only green small screen and the the 5.25" floppy disks were cool....and state of the art then......not so much now...
Part of the reason engine outputs are so high now compared to then on crap fuel is the processing power of their ECU....plus direct injection.... To really get the most out of a custom built high compression RACE 928 engine....you do need a modern ECU system...coil on plug, MAP, mutliple knock sensing, sequential injection (batch fire...really), EGT or multiple 02 sensors....the very best today always sample 02.....never fall back to base maps...no need....
Remember GTS owners complaining about pinging on our crap California gas.....that was only 10.4-1 and needed 93 octane or octane boosters to not ping...
Given that race fuel 110+ is VERY expensive, like $10+ per gallon....I still think E85 is the way to go..under $3 per gallon pretty easy to install a tank-pump in your trailer and bring your own fuel racing...saving at least $7 per gallon goes a long way even if you burn 40% more.....some bigger injectors, fuel pump & tuning.....I'd even think the LH-EZK might be able to handle it
Part of the reason engine outputs are so high now compared to then on crap fuel is the processing power of their ECU....plus direct injection.... To really get the most out of a custom built high compression RACE 928 engine....you do need a modern ECU system...coil on plug, MAP, mutliple knock sensing, sequential injection (batch fire...really), EGT or multiple 02 sensors....the very best today always sample 02.....never fall back to base maps...no need....
Remember GTS owners complaining about pinging on our crap California gas.....that was only 10.4-1 and needed 93 octane or octane boosters to not ping...
Given that race fuel 110+ is VERY expensive, like $10+ per gallon....I still think E85 is the way to go..under $3 per gallon pretty easy to install a tank-pump in your trailer and bring your own fuel racing...saving at least $7 per gallon goes a long way even if you burn 40% more.....some bigger injectors, fuel pump & tuning.....I'd even think the LH-EZK might be able to handle it
First, I don't think the difference between $10 per gallon and $3 per gallon is economically significant. You have to adjust for the amount of E85 you have inject per unit of air first, which normalizes the price to about $4.50. So you're looking for $5.50 discount relative to race gas. How many gallons are you burning such that this moves the needle compared to other costs of racing? I don't see this a place to economize.
Second, whether you run E85 or high-octane race gas, advancing the ignition too much in a race motor will still break it. It'll blow head gaskets, overheat and crack pistons, crack cylinder towers, etc. High octane rating is not the panacea that allows you to do whatever you want. You still have to tune the engine such that the peak cylinder pressure is within the engine's limits and that peak cylinder pressure takes place at a sensible crank angle.
Third, we're talking about the kinds of issues here where old ECUs and new ECUs don't make much of a difference, as long as they are used correctly. If you're running a 90% duty cycle of your fuel injectors, how is going from batch fire to sequential going to help peak power? If your ignition timing is 10 degrees too early for the engine, what difference does it make to the engine whether it was EZ-K from the eighties or something newer that did it? I would like to hear more about the specific issues that need to be addressed using newer computers, instead of just general statements that old computers can't do it. (The stock 928 MAF sensor is another matter...) Have you considered what other things are different with the new engines and the old 928s other than the ECUs? How about the cooling system? Cylinder specific or just flowing thru the block? How about cam timing? Variable valve timing or static valve timing? How about piston cooling with spray jets? How about optimized design for crankcase air flow and oil spray patterns? New computers alone don't turn your 928 S4 engine into a modern BMW engine.
07-27-2018 | 12:36 PM
#321
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From: MA
Clarification information:
The cracks on the domes of the pistons are continuations of the cracks at the base of the pin bosses on the underside.
On some of the pistons, it is difficult to figure out what is keeping the entire pin boss structure attached to the rest of the piston.
The dome of the completely failed piston/rod actually has "divots" above the what is left of the piston bosses.
Because of the extent of the damage and the fact that every piston is broken, I have a tough time imagining one "super knock" being responsible.
The cracks on the domes of the pistons are continuations of the cracks at the base of the pin bosses on the underside.
On some of the pistons, it is difficult to figure out what is keeping the entire pin boss structure attached to the rest of the piston.
The dome of the completely failed piston/rod actually has "divots" above the what is left of the piston bosses.
Because of the extent of the damage and the fact that every piston is broken, I have a tough time imagining one "super knock" being responsible.
I agree that a single super knock will not take out eight pistons.
If both the crowns and pin bosses are cracked and the pistons have overheated, then I would guess repeated cycles that have started with pre-ignition and developed into knock.
07-27-2018 | 12:46 PM
#322
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From: saratoga, ca
Thank you for the additional information. When you have time, please post more photos of the damaged components.
I agree that a single super knock will not take out eight pistons.
If both the crowns and pin bosses are cracked and the pistons have overheated, then I would guess repeated cycles that have started with pre-ignition and developed into knock.
07-27-2018 | 01:14 PM
#323
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From: MA
Again, my question to you was, why do you think its pre-ignition when you need some type of superhot, or burning amber to create pre-ignition? it doesnt have much to do with compression , as you are not all the way through the compression cycle. why couldnt this issue, obviusly some major detonation, be caused by a lean mixture , (near stoich) causing the detonation and this could happen with the correct octane fuel. too advanced spark, too lean of a mixture, all could cause this.. no?? we have already seen these factors in action on one of marks engines. why couldnt that happen if there was some changes to the tune?
I don't see how spark knock could similarly overheat the pistons.
It is possible that initial spark knock caused, for example, broken insulation in the spark plugs that lead to subsequent pre-ignition. Or caused ring flutter and mixture of diluted oil droplets into the combustion chamber.
Excessively rich mixture can often cause pre-ignition, so "hammer" tuning it way rich doesn't make the engine safe. This is because the combustion chamber runs out of oxygen and the fuel droplets that may remain close to the chamber walls or in various crevices will burn very slowly, glowing like ambers. Also, excess fuel on the bore walls will dilute oil on the bore walls and make it more likely to enter the combustion chamber and form similar glow-plug embers.
07-27-2018 | 01:27 PM
#324
Former Vendor
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From: Anaheim
None of the spark plugs show any signs of the heat range being too hot.
No cracked or damaged insulators and no damage to any of the electrodes. Porcelain looks perfect...no blistering...nothing strange, except for color and an occasional little "ball" stuck to the strap.
I wouldn't hesitate to put any of the spark plugs right back into another engine.
No cracked or damaged insulators and no damage to any of the electrodes. Porcelain looks perfect...no blistering...nothing strange, except for color and an occasional little "ball" stuck to the strap.
I wouldn't hesitate to put any of the spark plugs right back into another engine.
07-27-2018 | 02:03 PM
#325
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From: Anaheim
For what it is worth, my machinist (older than me [that is actually possible] and has been an engine builder/machinist his entire life) asked if he could have one of the pistons to put under his counter to show people.
He said it was the most perfect example of detonation he had ever seen.....
I'm not sure it is important for us to decide/know if the failure is pre-ignition or detonation....almost a moot point, in this failure. It seems like people on the Internet toss around and mix the two different failure modes so much that they become almost one in the same.
Here's my "spin" on this failure and why I go with detonation:
When I was building Big Block Chevy engines for competition use, I had to be really careful to tell people to limit the ignition timing in the "open chamber" engines. If they ran anywhere near the total timing in the open chamber engines that they had previously ran in the closed chamber engines, the intake valves would get so hot they would "tulip", the edges of the pistons would start to melt, and the center electrode of the spark plug would melt. I always considered that to be pre-ignition, because as soon as I "repaired the engines" and made sure the ignition timing was reduced, everything was fine....with no other changes.
Once there are cracks in both the pistons and the rods (especially in the rods, like the example in this engine), there is definitely something different going on.
I don't believe anyone could crack a Carrillo connecting rod down the middle with anything but a huge blow.....or multiple huge blows.
And that fits my definition of detonation.
He said it was the most perfect example of detonation he had ever seen.....
I'm not sure it is important for us to decide/know if the failure is pre-ignition or detonation....almost a moot point, in this failure. It seems like people on the Internet toss around and mix the two different failure modes so much that they become almost one in the same.
Here's my "spin" on this failure and why I go with detonation:
When I was building Big Block Chevy engines for competition use, I had to be really careful to tell people to limit the ignition timing in the "open chamber" engines. If they ran anywhere near the total timing in the open chamber engines that they had previously ran in the closed chamber engines, the intake valves would get so hot they would "tulip", the edges of the pistons would start to melt, and the center electrode of the spark plug would melt. I always considered that to be pre-ignition, because as soon as I "repaired the engines" and made sure the ignition timing was reduced, everything was fine....with no other changes.
Once there are cracks in both the pistons and the rods (especially in the rods, like the example in this engine), there is definitely something different going on.
I don't believe anyone could crack a Carrillo connecting rod down the middle with anything but a huge blow.....or multiple huge blows.
And that fits my definition of detonation.
07-27-2018 | 02:21 PM
#326
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From: Oman
There can be little doubt that pre-ignition has caused the overheating as the coked oil suggests a temperature in excess of 315C. That pre-ignition can melt pistons is a fact and that requires a metal temperature circa 600C and based on the example I saw it was bang in the middle of the piston so much so that we joked about drilling it out and inserting a bolt to seal it back up [needless to say we did not]! This failure did not get that far. Because pre-ignition happens before the normal timing point, it is quite conceivable that knocks occur in much the same fashion as they do with too much advance but they happen whilst the piston is still compressing. What they are classed as and how many events happen remains to be seen but I suspect such event is not a single occurrence if indeed that is implicit by the term Super Knock.
The damage that Greg describes has to have been caused by some kind of hammering force and that suggests a series of detonations on a strata with greatly reduced tensile capabilities. The greatest unsupported length on the piston is at the centre of the crown and cracks will likely propagate form that location. That the pin bosses let go first on the cylinder that failed is what it is but the fact that all the pistons are showing similar behaviour tells us that the problem was manifest and to some extent it was pot luck as to which one let go first. A crack starting on the centre of the crown will not let go but cracks in the gudgeon pin boss area most certainly will.
Every failure has a root cause- just a question of getting to the bottom of what caused it.
The damage that Greg describes has to have been caused by some kind of hammering force and that suggests a series of detonations on a strata with greatly reduced tensile capabilities. The greatest unsupported length on the piston is at the centre of the crown and cracks will likely propagate form that location. That the pin bosses let go first on the cylinder that failed is what it is but the fact that all the pistons are showing similar behaviour tells us that the problem was manifest and to some extent it was pot luck as to which one let go first. A crack starting on the centre of the crown will not let go but cracks in the gudgeon pin boss area most certainly will.
Every failure has a root cause- just a question of getting to the bottom of what caused it.
07-27-2018 | 02:30 PM
#327
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Contaminating the discussion some...
"Spark knock" from poor timing and fuel grade manifests early with hammered edges on the piston tops, often pinching the top rings and eventually fracturing the oil scrapers. Then more oil is left on the cylinder walls. The plug gets too hot and is effectively a "glow plug" with an oil-contaminated fuel charge, and you get both the heating and the hammering. Once there's excess oil there's not a lot that knock sensors or fuel adjustment can do to stop the death spiral.
When I was racing the 2-stroke Yamaha sports racer, our tuner would look down through the plug hole, and could tell us whether the crank bearings were flattened just looking at the bloom. Yamaha quickly added guidance with special versions of their Yamalube, and barrels of their own race fuel. The fuel passed all the SCCA field tests so it could be used in a class that was "pump gas" limited. Engines actually lasted when the right fuel and their oil was used. The oil bottle were identical to what was offered on the shelf at dealers, including part numbers, but wasn't the same inside apparently.
Considering how forgiving E85 is in "recreational" race engines, it's getting hard to justify building one these days to run on gasoline. It just takes 2.x the fuel mass to make the power, and let the fuel cool the chambers and pistons along the way. I can think of only one better use for ethanol.
"Spark knock" from poor timing and fuel grade manifests early with hammered edges on the piston tops, often pinching the top rings and eventually fracturing the oil scrapers. Then more oil is left on the cylinder walls. The plug gets too hot and is effectively a "glow plug" with an oil-contaminated fuel charge, and you get both the heating and the hammering. Once there's excess oil there's not a lot that knock sensors or fuel adjustment can do to stop the death spiral.
When I was racing the 2-stroke Yamaha sports racer, our tuner would look down through the plug hole, and could tell us whether the crank bearings were flattened just looking at the bloom. Yamaha quickly added guidance with special versions of their Yamalube, and barrels of their own race fuel. The fuel passed all the SCCA field tests so it could be used in a class that was "pump gas" limited. Engines actually lasted when the right fuel and their oil was used. The oil bottle were identical to what was offered on the shelf at dealers, including part numbers, but wasn't the same inside apparently.
Considering how forgiving E85 is in "recreational" race engines, it's getting hard to justify building one these days to run on gasoline. It just takes 2.x the fuel mass to make the power, and let the fuel cool the chambers and pistons along the way. I can think of only one better use for ethanol.
07-27-2018 | 03:15 PM
#328
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From: Friday Harbor, WA
This, I think, is key:
In fact it seems to me that pre-ignition would almost certainly lead to detonation, just as dialing in extra 10-deg of ignition advance would almost certainly lead to detonation. And of course the limit on ignition advance is octane, pressure, and temperature. All are variables to a degree (octane varies, altitude effects combustion pressure, track temp determines intake air temp, etc) so the trick is developing a tune that is safe in worst-case conditions. Of course the EZK for 87+ cars) detects knocks and pulls timing as needed, within limits. And Sharktuner of course monitors and logs that, which is an excellent gauge for that safety margin.
So here's a crazy idea: Take along a Sharktuner for at least the practice laps, and find out for sure if the engine is safe for that day's conditions, fuel, etc. And if it isn't, then fix it. It's simple and stupid-cheap compared to risking an engine.
So here's a crazy idea: Take along a Sharktuner for at least the practice laps, and find out for sure if the engine is safe for that day's conditions, fuel, etc. And if it isn't, then fix it. It's simple and stupid-cheap compared to risking an engine.
07-27-2018 | 03:17 PM
#329
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From: MA
For what it is worth, my machinist (older than me [that is actually possible] and has been an engine builder/machinist his entire life) asked if he could have one of the pistons to put under his counter to show people.
He said it was the most perfect example of detonation he had ever seen.....
I'm not sure it is important for us to decide/know if the failure is pre-ignition or detonation....almost a moot point, in this failure. It seems like people on the Internet toss around and mix the two different failure modes so much that they become almost one in the same.
Here's my "spin" on this failure and why I go with detonation:
When I was building Big Block Chevy engines for competition use, I had to be really careful to tell people to limit the ignition timing in the "open chamber" engines. If they ran anywhere near the total timing in the open chamber engines that they had previously ran in the closed chamber engines, the intake valves would get so hot they would "tulip", the edges of the pistons would start to melt, and the center electrode of the spark plug would melt. I always considered that to be pre-ignition, because as soon as I "repaired the engines" and made sure the ignition timing was reduced, everything was fine....with no other changes.
He said it was the most perfect example of detonation he had ever seen.....
I'm not sure it is important for us to decide/know if the failure is pre-ignition or detonation....almost a moot point, in this failure. It seems like people on the Internet toss around and mix the two different failure modes so much that they become almost one in the same.
Here's my "spin" on this failure and why I go with detonation:
When I was building Big Block Chevy engines for competition use, I had to be really careful to tell people to limit the ignition timing in the "open chamber" engines. If they ran anywhere near the total timing in the open chamber engines that they had previously ran in the closed chamber engines, the intake valves would get so hot they would "tulip", the edges of the pistons would start to melt, and the center electrode of the spark plug would melt. I always considered that to be pre-ignition, because as soon as I "repaired the engines" and made sure the ignition timing was reduced, everything was fine....with no other changes.
07-27-2018 | 03:36 PM
#330
Former Vendor
Joined: Feb 2005
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From: Anaheim
Contaminating the discussion some...
"Spark knock" from poor timing and fuel grade manifests early with hammered edges on the piston tops, often pinching the top rings and eventually fracturing the oil scrapers. Then more oil is left on the cylinder walls. The plug gets too hot and is effectively a "glow plug" with an oil-contaminated fuel charge, and you get both the heating and the hammering. Once there's excess oil there's not a lot that knock sensors or fuel adjustment can do to stop the death spiral.
When I was racing the 2-stroke Yamaha sports racer, our tuner would look down through the plug hole, and could tell us whether the crank bearings were flattened just looking at the bloom. Yamaha quickly added guidance with special versions of their Yamalube, and barrels of their own race fuel. The fuel passed all the SCCA field tests so it could be used in a class that was "pump gas" limited. Engines actually lasted when the right fuel and their oil was used. The oil bottle were identical to what was offered on the shelf at dealers, including part numbers, but wasn't the same inside apparently.
Considering how forgiving E85 is in "recreational" race engines, it's getting hard to justify building one these days to run on gasoline. It just takes 2.x the fuel mass to make the power, and let the fuel cool the chambers and pistons along the way. I can think of only one better use for ethanol.
"Spark knock" from poor timing and fuel grade manifests early with hammered edges on the piston tops, often pinching the top rings and eventually fracturing the oil scrapers. Then more oil is left on the cylinder walls. The plug gets too hot and is effectively a "glow plug" with an oil-contaminated fuel charge, and you get both the heating and the hammering. Once there's excess oil there's not a lot that knock sensors or fuel adjustment can do to stop the death spiral.
When I was racing the 2-stroke Yamaha sports racer, our tuner would look down through the plug hole, and could tell us whether the crank bearings were flattened just looking at the bloom. Yamaha quickly added guidance with special versions of their Yamalube, and barrels of their own race fuel. The fuel passed all the SCCA field tests so it could be used in a class that was "pump gas" limited. Engines actually lasted when the right fuel and their oil was used. The oil bottle were identical to what was offered on the shelf at dealers, including part numbers, but wasn't the same inside apparently.
Considering how forgiving E85 is in "recreational" race engines, it's getting hard to justify building one these days to run on gasoline. It just takes 2.x the fuel mass to make the power, and let the fuel cool the chambers and pistons along the way. I can think of only one better use for ethanol.
No matter what Carrillo said about the first failure and what I believe happened, this engine still got run on monkey **** mixed with a splash of race fuel....to "save" a few bucks on real race fuel. (Just suppose, for an instant, that the first engine failed from detonation, as one of the two choices that Carrillo suggested. Now, If 110 octane costs $10 a gallon and one of these engines cost 30K to fix....now much race fuel does that buy? Is that math really so complex that only a rocket scientist can figure that out? And you are going to make a 30K bet that Carrillo and your engine builder are wrong and go ahead and run "the same fuel mix I've always ran" on the second engine?)
And you are suggesting that I should try and convince this particular individual into the expense of converting the fuel system/computer system over to be able to use E85.
That's just plain old funny.....