The moment of truth
04-23-2012, 12:11 AM
#16
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04-23-2012, 12:12 AM
#17
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Remember, AFR is only half the equation. The other half is timing...
I don't see any tell-tale signs of detonation. (he was running high octane fuel)
However, there was most likely way too much timing for that boot pressure/load, causing very high cylinder pressures, resulting in the failure.
I don't see any tell-tale signs of detonation. (he was running high octane fuel)
However, there was most likely way too much timing for that boot pressure/load, causing very high cylinder pressures, resulting in the failure.
04-23-2012, 12:24 AM
#18
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I have personally run that much boost, and Sid has run much harder than 26psi. But that does not mean I would suggest that someone go and try it - especially for anything besides a street/dyno run.
Additionally, anything around or above 400rwhp, and you are at the limits of stock internals, IMO.
04-23-2012, 12:33 AM
#19
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Remember, AFR is only half the equation. The other half is timing...
I don't see any tell-tale signs of detonation. (he was running high octane fuel)
However, there was most likely way too much timing for that boot pressure/load, causing very high cylinder pressures, resulting in the failure.
I don't see any tell-tale signs of detonation. (he was running high octane fuel)
However, there was most likely way too much timing for that boot pressure/load, causing very high cylinder pressures, resulting in the failure.
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Lart: Man that made 951 values rise. XD
04-23-2012, 12:41 AM
#20
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That really depends on what you are trying to accomplish...
I have personally run that much boost, and Sid has run much harder than 26psi. But that does not mean I would suggest that someone go and try it - especially for anything besides a street/dyno run.
Additionally, anything around or above 400rwhp, and you are at the limits of stock internals, IMO.
I have personally run that much boost, and Sid has run much harder than 26psi. But that does not mean I would suggest that someone go and try it - especially for anything besides a street/dyno run.
Additionally, anything around or above 400rwhp, and you are at the limits of stock internals, IMO.
04-23-2012, 01:25 AM
#21
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Usually we set the overboost limit to 18psi on pump.
It is a balancing act. For a street car, we can tend to get away with being a little bit more aggressive on boost pressure. Pulling out timing will help keep the motor intact, but does raise EGT. For extended WOT / High-load situations, this is not desirable (such as a track car).
It is a balancing act. For a street car, we can tend to get away with being a little bit more aggressive on boost pressure. Pulling out timing will help keep the motor intact, but does raise EGT. For extended WOT / High-load situations, this is not desirable (such as a track car).
04-23-2012, 02:12 AM
#22
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It is however a process of diminishing returns. I can tell you from personal experience that if timing it left the same there's a nice "pull" difference between 27 and 35psi but without pulling timing way back my knock counts went through the roof. This whay the 35psi set was on a momentary steering wheel button. To keep knock counts low, timing had to be pulled back so far there really wasn't much difference between a safe 27 and a safe 35psi. 26-27psi was about the limit of usable power gain. This year I'm trying some real crazy stuff so we will see if that changes. Btw Lart, I also used to run a Xylene mix before falling in love with E85. I used to buy it from a local paint store in 5 gallon buckets. I was very usefull stuff, put in my gas tank, use it to kill weed, make an awesome adhesive remover...too bad its so toxic. lol
Now to the OP topic. This failure is not from overboost although whatever boost he was running at the time certainly did not help and I am sure added to the failure, however it was not the cause. The plugs looked good, bottoms of valves looked normal for a 25 year old 951 engine, fuel mixture was correct and as Rogue stated, no signs detonation.
This is an overheating failure that was the root cause. He did suck some coolant in the intake was everthing went to hell but that was an after effect which cause the engine to immediately shut down. Had water been the cause there would typically be many bits of metal to gathered and broken rods. I've done quite a bit of off roading with my toys so I've hydrolocked a good number of engines, the damage was always catastrophic.
The plastic radiator drain plug was found to be broken in the manner that they break. Coolant presumably became low enough to boil and overheat the engine which also caused a hose rupture thus allowing some coolant into the intake while it was overheated and already starting to weaken/crack. That combined with the high boost pressure was just too much for the seasoned cylinder wall... Poor little guy, probably kept up for a mile or so. *sniff* Tough little mutt.
04-23-2012, 02:39 AM
#23
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Usually we set the overboost limit to 18psi on pump.
It is a balancing act. For a street car, we can tend to get away with being a little bit more aggressive on boost pressure. Pulling out timing will help keep the motor intact, but does raise EGT. For extended WOT / High-load situations, this is not desirable (such as a track car).
It is a balancing act. For a street car, we can tend to get away with being a little bit more aggressive on boost pressure. Pulling out timing will help keep the motor intact, but does raise EGT. For extended WOT / High-load situations, this is not desirable (such as a track car).
04-23-2012, 02:41 AM
#24
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04-23-2012, 03:02 AM
#25
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04-23-2012, 05:09 AM
#27
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27-35psi is possible on these blocks if tuned perfect on E-85. Mine is still in project mode but I'm hoping to have it back on the track at least once this year and can show anyone who wants to see. It is however a process of diminishing returns. I can tell you from personal experience that if timing it left the same there's a nice "pull" difference between 27 and 35psi but without pulling timing way back my knock counts went through the roof. This whay the 35psi set was on a momentary steering wheel button. To keep knock counts low, timing had to be pulled back so far there really wasn't much difference between a safe 27 and a safe 35psi. 26-27psi was about the limit of usable power gain. This year I'm trying some real crazy stuff so we will see if that changes.
Btw Lart, I also used to run a Xylene mix before falling in love with E85. I used to buy it from a local paint store in 5 gallon buckets. I was very usefull stuff, put in my gas tank, use it to kill weed, make an awesome adhesive remover...too bad its so toxic. lol
Now to the OP topic. This failure is not from overboost although whatever boost he was running at the time certainly did not help and I am sure added to the failure, however it was not the cause. The plugs looked good, bottoms of valves looked normal for a 25 year old 951 engine, fuel mixture was correct and as Rogue stated, no signs detonation.
This is an overheating failure that was the root cause. He did suck some coolant in the intake was everthing went to hell but that was an after effect which cause the engine to immediately shut down. Had water been the cause there would typically be many bits of metal to gathered and broken rods. I've done quite a bit of off roading with my toys so I've hydrolocked a good number of engines, the damage was always catastrophic.
The plastic radiator drain plug was found to be broken in the manner that they break. Coolant presumably became low enough to boil and overheat the engine which also caused a hose rupture thus allowing some coolant into the intake while it was overheated and already starting to weaken/crack. That combined with the high boost pressure was just too much for the seasoned cylinder wall... Poor little guy, probably kept up for a mile or so. *sniff* Tough little mutt.
It is however a process of diminishing returns. I can tell you from personal experience that if timing it left the same there's a nice "pull" difference between 27 and 35psi but without pulling timing way back my knock counts went through the roof. This whay the 35psi set was on a momentary steering wheel button. To keep knock counts low, timing had to be pulled back so far there really wasn't much difference between a safe 27 and a safe 35psi. 26-27psi was about the limit of usable power gain. This year I'm trying some real crazy stuff so we will see if that changes. Btw Lart, I also used to run a Xylene mix before falling in love with E85. I used to buy it from a local paint store in 5 gallon buckets. I was very usefull stuff, put in my gas tank, use it to kill weed, make an awesome adhesive remover...too bad its so toxic. lol
Now to the OP topic. This failure is not from overboost although whatever boost he was running at the time certainly did not help and I am sure added to the failure, however it was not the cause. The plugs looked good, bottoms of valves looked normal for a 25 year old 951 engine, fuel mixture was correct and as Rogue stated, no signs detonation.
This is an overheating failure that was the root cause. He did suck some coolant in the intake was everthing went to hell but that was an after effect which cause the engine to immediately shut down. Had water been the cause there would typically be many bits of metal to gathered and broken rods. I've done quite a bit of off roading with my toys so I've hydrolocked a good number of engines, the damage was always catastrophic.
The plastic radiator drain plug was found to be broken in the manner that they break. Coolant presumably became low enough to boil and overheat the engine which also caused a hose rupture thus allowing some coolant into the intake while it was overheated and already starting to weaken/crack. That combined with the high boost pressure was just too much for the seasoned cylinder wall... Poor little guy, probably kept up for a mile or so. *sniff* Tough little mutt.
