The Fastest 928 of all time, blows an Engine!
04-23-2012, 03:40 PM
#46
Three Wheelin'
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Sorry to hear of this. Glad you are OK, which is the most important thing. Hope there are salvageable components.
I'm sure Greg will decipher the puzzle. Good luck with the new build!
I'm sure Greg will decipher the puzzle. Good luck with the new build!
Last edited by 86'928S MeteorGrey; 04-23-2012 at 08:52 PM.
04-23-2012, 05:01 PM
#47
Rennlist Member
I think it was the O rings on the SRBs.
Seriously, Mark has had amazing reliablity for how hard he runs, but mechanical parts break. I'm sure there is a whole field of mathamatics to proove what anybody with a race car or a boat already knows.
Seriously, Mark has had amazing reliablity for how hard he runs, but mechanical parts break. I'm sure there is a whole field of mathamatics to proove what anybody with a race car or a boat already knows.
04-23-2012, 06:12 PM
#48
Nordschleife Master
Maybe call in Rob for an Auto topsy?
Nice how bad news here often has a silver lining, two offers of an alternate 928 seat so Mark doesn't have to suffer in that other Porsche.
Nice how bad news here often has a silver lining, two offers of an alternate 928 seat so Mark doesn't have to suffer in that other Porsche.
04-24-2012, 01:22 AM
#49
By Puyi
Generally all mechanical parts have a life span due to mechanical stress as apposed to just wearing out like an engine's bore. It just depends on the level of stress the components can take and that will depend on the material and design.
Basically if the part stressed beyond what the material can bounce back from or yield to it has suffered damage or deformation. Also all materials have different ductility levels and even the same materials can have different ductility due to different treatments such as heat treatments.
Aluminum's yield levels are generally is quite low whereas a spring steel is very high. However you don't make con rods out of spring steel. So depending how hard the parts can be punished and how close they are being stressed to their yield points gives the lifespan.
The first thing to break when they extended engine milage on the F1 engines was the blocks. This was cured by just making them thicker. In NASCAR the cranks get lifed out in a range of 12 to 15 million power cycles. However if you had the same crank and didn't have same power and same hard use like NASCAR ovals, you would probably wear them out before you stressed them out.
V8 Supercar is a perfect example of this, same basic parts, slightly lower power per litre, less revs and less full throttle running. The engines last much longer, pistons do 1 race in NASCAR or a race weekend but the same pistons in V8 Supercar do 4 to 5 race weekend equivalents.
The other interesting thing that can happen to rods when used with a dry sump, they can suffer from not enough oil cooling and
lubrication at the wrist pin and then get overly hot and this changes the heat treatment of the steel and the steel becomes weak, soft and breaks. Got to say this happens much more when there is no brass/copper bush.
The other issue that occurs in this area of the engine is cracking around the piston pin bosses, if the pistons in this engine are Mahle factory pistons, they wear quite well but when pushed hard in terms of G forces the piston pin will flex as the factory pins are may not be and in general race engine terms well supported. This potentially would then be compounded by the Mahle piston material which is brittle and subject to cracking.
The greater the distance from the edge of the rod eye to the inner edge of the piston. The Porsche rod is 27 mm wide and generally aftermarket rods are narrower and this will add to the stress in this area. Apart from the stroke which effects piston speed, so does the rod to stroke ratio. I think Mark has 968 pistons but I have no idea of what stroke or rods however taking a guess at a ratio around 1.6 to 1, the loads would escalate once the engine went over 7,000.
Again in regards to piston cracking, the only real advantage that the softer 2618 material has is it's ability to be more plastic and as such deform without cracking. Both materials have about the same strength at operating temperature and both materials are very strong. Just different characteristics and ability. I'm sure plenty of folks on this board have seen broken ring lands on Porsche 928 pistons. I suspect that is due to detonation which is a problem for stiff hard pistons.
Anyway I am sure we will find out soon what has gone on and I am sure it will be the better for it.
How many hours of use for that engine since complete rebuild?
There is much reason that make a race engine to be rebuild every X hours, but let me know.
There is much reason that make a race engine to be rebuild every X hours, but let me know.
Basically if the part stressed beyond what the material can bounce back from or yield to it has suffered damage or deformation. Also all materials have different ductility levels and even the same materials can have different ductility due to different treatments such as heat treatments.
Aluminum's yield levels are generally is quite low whereas a spring steel is very high. However you don't make con rods out of spring steel. So depending how hard the parts can be punished and how close they are being stressed to their yield points gives the lifespan.
The first thing to break when they extended engine milage on the F1 engines was the blocks. This was cured by just making them thicker. In NASCAR the cranks get lifed out in a range of 12 to 15 million power cycles. However if you had the same crank and didn't have same power and same hard use like NASCAR ovals, you would probably wear them out before you stressed them out.
V8 Supercar is a perfect example of this, same basic parts, slightly lower power per litre, less revs and less full throttle running. The engines last much longer, pistons do 1 race in NASCAR or a race weekend but the same pistons in V8 Supercar do 4 to 5 race weekend equivalents.
The other interesting thing that can happen to rods when used with a dry sump, they can suffer from not enough oil cooling and
lubrication at the wrist pin and then get overly hot and this changes the heat treatment of the steel and the steel becomes weak, soft and breaks. Got to say this happens much more when there is no brass/copper bush.
The other issue that occurs in this area of the engine is cracking around the piston pin bosses, if the pistons in this engine are Mahle factory pistons, they wear quite well but when pushed hard in terms of G forces the piston pin will flex as the factory pins are may not be and in general race engine terms well supported. This potentially would then be compounded by the Mahle piston material which is brittle and subject to cracking.
The greater the distance from the edge of the rod eye to the inner edge of the piston. The Porsche rod is 27 mm wide and generally aftermarket rods are narrower and this will add to the stress in this area. Apart from the stroke which effects piston speed, so does the rod to stroke ratio. I think Mark has 968 pistons but I have no idea of what stroke or rods however taking a guess at a ratio around 1.6 to 1, the loads would escalate once the engine went over 7,000.
Again in regards to piston cracking, the only real advantage that the softer 2618 material has is it's ability to be more plastic and as such deform without cracking. Both materials have about the same strength at operating temperature and both materials are very strong. Just different characteristics and ability. I'm sure plenty of folks on this board have seen broken ring lands on Porsche 928 pistons. I suspect that is due to detonation which is a problem for stiff hard pistons.
Anyway I am sure we will find out soon what has gone on and I am sure it will be the better for it.
Last edited by slate blue; 04-24-2012 at 03:07 AM. Reason: English Grammar
04-24-2012, 06:28 AM
#50
Racer
"I suspect that is due to detonation which is a problem for stiff hard pistons."
That is what I was thinking about.
Even if the engine has been adapted to be raced, In fact, the materials used on it mostly come from road car engine.
Road car engine are maked to run during 2000 to 3000 Hours. You can divide it by number of cycle. The strain on that engine in race condition is aimed to one tenth to one twentieth of normal use. So a engine like that should be refreshed every 150 Hours. I assume that it is a very large approximation. But it takes an indication of "normality".
If you want to really know what happened, and find a solution, you probably waste a lot of time and not be sure of the real diagnosis of the failure. What you know, is that the engine raced during X hours before pistons decide to get free!
Good luck for repairs
That is what I was thinking about.
Even if the engine has been adapted to be raced, In fact, the materials used on it mostly come from road car engine.
Road car engine are maked to run during 2000 to 3000 Hours. You can divide it by number of cycle. The strain on that engine in race condition is aimed to one tenth to one twentieth of normal use. So a engine like that should be refreshed every 150 Hours. I assume that it is a very large approximation. But it takes an indication of "normality".
If you want to really know what happened, and find a solution, you probably waste a lot of time and not be sure of the real diagnosis of the failure. What you know, is that the engine raced during X hours before pistons decide to get free!
Good luck for repairs
04-24-2012, 10:13 AM
#52
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I don't race anything any more, and never raced anything very much, so I am at best an armchair racer. Some years ago I decided to subject all steel parts in my engines to cryogenic treatment. Why? I am of the understanding that all NASCAR and F1 engines are subjected to such treatment, so I figured it would not hurt. Many are aware of the benefits of cryo treatment of brake rotors...so, why not the rest of the stressed parts of an engine? I understand NASCAR and F1 tend to do blocks and eveything else as well
It is not an expensive process when compaired to the cost of building a performance engine. Crank, camshafts, lifters, rods, piston pins, valve springs, head bolts, main bolts, etc. all go for treatment.
Just a few thoughts...if I were spending many thousands on a 928 race engine, I would certainly spend a few hundred on cryo....
It is not an expensive process when compaired to the cost of building a performance engine. Crank, camshafts, lifters, rods, piston pins, valve springs, head bolts, main bolts, etc. all go for treatment.
Just a few thoughts...if I were spending many thousands on a 928 race engine, I would certainly spend a few hundred on cryo....
04-24-2012, 01:28 PM
#54
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"I suspect that is due to detonation which is a problem for stiff hard pistons."
That is what I was thinking about.
Even if the engine has been adapted to be raced, In fact, the materials used on it mostly come from road car engine.
Road car engine are maked to run during 2000 to 3000 Hours. You can divide it by number of cycle. The strain on that engine in race condition is aimed to one tenth to one twentieth of normal use. So a engine like that should be refreshed every 150 Hours. I assume that it is a very large approximation. But it takes an indication of "normality".
If you want to really know what happened, and find a solution, you probably waste a lot of time and not be sure of the real diagnosis of the failure. What you know, is that the engine raced during X hours before pistons decide to get free!
Good luck for repairs
That is what I was thinking about.
Even if the engine has been adapted to be raced, In fact, the materials used on it mostly come from road car engine.
Road car engine are maked to run during 2000 to 3000 Hours. You can divide it by number of cycle. The strain on that engine in race condition is aimed to one tenth to one twentieth of normal use. So a engine like that should be refreshed every 150 Hours. I assume that it is a very large approximation. But it takes an indication of "normality".
If you want to really know what happened, and find a solution, you probably waste a lot of time and not be sure of the real diagnosis of the failure. What you know, is that the engine raced during X hours before pistons decide to get free!
Good luck for repairs
04-25-2012, 01:48 PM
#56
The Parts Whisperer
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Thanks for all the supportive comments. At the moment I am just considering all my options. I've had a few people show interest in carrying on the torch should I choose not to.
04-26-2012, 12:53 PM
#59
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Good eye, The driver in the video was very calm so looks slow but he was going around 100mph when I passed him I was doing around 115mph. Thats the last time I drove the car at T-Hill.
That video just about broke my heart first time I watched it, still hurts a little but I'm over it, mostly.
I replaced the motor and crashed the car 2 or 3 races later.That was even more devestating but that's racing **** happens.
Mark, I know you know this but I really do feel your pain and once again I'm glad you're OK and your welcome to use any one of my race cars anytime you would like. You might be one of the few people who could actually handle the 600hp supercharged Yellow Monster.
Sean
That video just about broke my heart first time I watched it, still hurts a little but I'm over it, mostly.
I replaced the motor and crashed the car 2 or 3 races later.That was even more devestating but that's racing **** happens.
Mark, I know you know this but I really do feel your pain and once again I'm glad you're OK and your welcome to use any one of my race cars anytime you would like. You might be one of the few people who could actually handle the 600hp supercharged Yellow Monster.
Sean
04-26-2012, 03:08 PM
#60
The Parts Whisperer
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Thanks for the VERY generous off Sean.
