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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.
For our 928 S4 car engines run on pump gas, I think it is indeed highly likely that pre-ignition cycles develop to also knock cycles, especially at full load and lower rpms. In effect, the low fuel octane can act as an early warning mechanism with knock sensing, at least as long as someone is actively looking at knock counts. The one caveat is that if the pre-ignition induced knock happens during the TDC window, then many knock sensing systems ignore it as there’s too much piston slap noise that would otherwise confuse the knock detection logic. I don’t know how EZK windows is listening interval as a function of crank angle.
For aero piston engines, the margins of safety are so large that preignition doesn’t automatically cause knock on aviation fuel. So that’s why they have to detect pre-ignition from the CHT and EGT moving in opposite directions.
Just suppose, for an instant, that the first engine failed from detonation, as one of the two choices that Carrillo suggested.
I wouldn't want to take the aftermarket performance parts supplier completely at face value when there's an engine failure. They are conflicted. Even if they had supplied a rod made of balsa wood and the rod had burned into ashes inside the engine, they'd still come back with either irregular combustion or excessive engine speed.
The pictures are as informative and much less conflicted, in my opinion.
10 years ago Todd told us that detonation causes a piston to handle 10 times the normal power of that hole. 91 octane is below the minimum on many current production cars, and therefore causes them to retard it from optimal tables. This is not new, and this is not conjecture.
10 years ago Todd told us that detonation causes a piston to handle 10 times the normal power of that hole. 91 octane is below the minimum on many current production cars, and therefore causes them to retard it from optimal tables. This is not new, and this is not conjecture.
How did he measure that cylinder pressure? I wonder, since you say that's not conjecture, I assume it was measured?
I can tell you from experience that fitting a cylinder pressure sensor integrated to the spark plug into the 928 S4 head and valve cover is not easy. Whether or not you go ALL GHETTO with the wires.
Or perhaps you're not familiar with what the word "conjecture" means.
I wouldn't want to take the aftermarket performance parts supplier completely at face value when there's an engine failure. They are conflicted. Even if they had supplied a rod made of balsa wood and the rod had burned into ashes inside the engine, they'd still come back with either irregular combustion or excessive engine speed.
The pictures are as informative and much less conflicted, in my opinion.
Not much left of either of the broken rods, from either engine (actually, there were more pieces of the first failed rod than this one.)
If there wasn't this amazing crack in #2 rod (I have not removed any others to see if they are also cracked), I would never had a real clue that the pounding that occurred was so severe. And it is quite a stretch for me to think that the worst cracked and damaged piston (still attached to the crankshaft) just happens to have had a defective Carrillo rod attached to it.....that would be silly, in my opinion.
I've found the engineering department at Carrillo to be an incredible resource....they have always seemed to be as interested in figuring out what failed as I have been.
However, if I was using Scat or Eagle rods, made in China, I'd "hear" your point better.
How did he measure that cylinder pressure? I wonder, since you say that's not conjecture, I assume it was measured?
I can tell you from experience that fitting a cylinder pressure sensor integrated to the spark plug into the 928 S4 head and valve cover is not easy. Whether or not you go ALL GHETTO with the wires.
Or perhaps you're not familiar with what the word "conjecture" means.
(...)
On an individual basis, destroyed engines require root cause analysts for the failure. So much happens in such a short time, it can be a challenge.
Detonation and pre-ignition breaks (or melts) pistons. Doing much more than a mass-produced family sedan engine using 91 octane is asking for both those events to happen. Many modern vehicles with >11:1 CR are removing timing above 110 degrees IAT, which equates to around 85-90 degrees ambient. Unless its 65 degrees out, you are driving around on a "compromised" table in high CR vehicles.
For the current engine in this thread - 91 octane gas is barely that when tested at random pumps. Controlled combustion looks very different on a piston, on valves, on the dyno, 02 sensors, and on spark plugs than does "uncontrolled" combustion (which encompasses pre-ignition and detonation).
Greg -
I did not catch in the beginning - what ECU is running this engine?
Last edited by dr bob; 07-27-2018 at 08:15 PM.
Reason: Thread clean-up
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.....
Laugh away. Then read it again.
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.
Then tell me what part of that is so funny that it doesn't apply to new "recreational" race engines being built today. Want to pretty much remove the common concerns about melting pistons and hammering rods? Yes it takes a modern engine management package. What's one of your race engines worth these days? Adding a couple $k is relatively cheap insurance. E85 is much more commonly available than race gas, better supporting folks who might drive their cars away from organized events. Justify away!
Then tell me what part of that is so funny that it doesn't apply to new "recreational" race engines being built today. Want to pretty much remove the common concerns about melting pistons and hammering rods? Yes it takes a modern engine management package. What's one of your race engines worth these days? Adding a couple $k is relatively cheap insurance. E85 is much more commonly available than race gas, better supporting folks who might drive their cars away from organized events. Justify away!
I completely understand the benefits and agree with your train of thought.
I'm just trying to imagine "selling" this idea to a dedicated, total minimalist.....Hell, another $200 worth of race gas would have solved the problem, too!
On an individual basis, destroyed engines require root cause analysts for the failure. So much happens in such a short time, it can be a challenge.
Detonation and pre-ignition breaks (or melts) pistons. Doing much more than a mass-produced family sedan engine using 91 octane is asking for both those events to happen. Many modern vehicles with >11:1 CR are removing timing above 110 degrees IAT, which equates to around 85-90 degrees ambient. Unless its 65 degrees out, you are driving around on a "compromised" table in high CR vehicles.
For the current engine in this thread - 91 octane gas is barely that when tested at random pumps. Controlled combustion looks very different on a piston, on valves, on the dyno, 02 sensors, and on spark plugs than does "uncontrolled" combustion (which encompasses pre-ignition and detonation).
Greg -
I did not catch in the beginning - what ECU is running this engine?
So the answer is you don’t know what “conjecture” means?
Last edited by dr bob; 07-27-2018 at 08:14 PM.
Reason: Thread Clean-Up
(...)
On an individual basis, destroyed engines require root cause analysts for the failure. So much happens in such a short time, it can be a challenge.
Detonation and pre-ignition breaks (or melts) pistons. Doing much more than a mass-produced family sedan engine using 91 octane is asking for both those events to happen. Many modern vehicles with >11:1 CR are removing timing above 110 degrees IAT, which equates to around 85-90 degrees ambient. Unless its 65 degrees out, you are driving around on a "compromised" table in high CR vehicles.
For the current engine in this thread - 91 octane gas is barely that when tested at random pumps. Controlled combustion looks very different on a piston, on valves, on the dyno, 02 sensors, and on spark plugs than does "uncontrolled" combustion (which encompasses pre-ignition and detonation).
Greg -
I did not catch in the beginning - what ECU is running this engine?
I'm just trying to imagine "selling" this idea to a dedicated, total minimalist.....Hell, another $200 worth of race gas would have solved the problem, too!
Perhaps a showcase with a blackened piston and a split rod, maybe a bit of the viewport from the side of the block would help illustrate the need well enough. For either solution.
Here's some pictures of the cracked rod from cylinder #2, with a spray on crack detector. I had to wipe away most of the "developer" off...the cracks are too big and just "bleed" everywhere. Truthfully, I'm amazed that this connecting rod didn't also become multiple pieces.....it certainly could not have been very far behind.
Here's some pictures of the cracked rod from cylinder #2, with a spray on crack detector. I had to wipe away most of the "developer" off...the cracks are too big and just "bleed" everywhere. Truthfully, I'm amazed that this connecting rod didn't also become multiple pieces.....it certainly could not have been very far behind.
Here's a picture of the top of #2 piston. The dye penetrant didn't work perfectly. There's a crack going almost straight up, from near the upper end of the lower right crack, if you look closely.
Note the "pitting" on the top of the piston. I bead blasted the top of this piston at 20psi, to get rid of the burned on oil.
Note the marks from the piston hitting the cylinder head on the right edge. This piston had "expanded" about .030" and was that far out of the cylinder, hitting the edge of the combustion chamber.
It's really not very often that one gets such great pieces to look at, out of an exploded engine. Most engine failures involve one cylinder and it is sometimes tough to figure out what happened exactly.
I get sent an amazing amount of engine pieces to look at and try to figure out what happened, from all different kinds of engines, from all different people. Somewhere out there, is something written (or someone telling people) to send broken engine pieces to Greg Brown, when no one else can figure out what happened.....
This engine is a "school book" primer on detonation....or pre-ignition....I don't care what you want to call it.
07-27-2018, 03:36 PM
