Drilled Crank Thoughts...
02-29-2008, 11:11 AM
#346
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Maybe Porsche should have called The General, they were spinning pushrod small blocks past 7k in the Trans-Am series.
02-29-2008, 11:20 AM
#347
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Yes, the 928 engine. And hundreds of others. Making them run better. Sigh.
I think Porsche tried to develop a motor that shifted reliably at, say, 7500 rpms. This is hardly unreasonable for a company with a racing heritage developing a clean sheet OHC V8 in the late 1960s. They had to scale that expectation back. Just like Maybach had to scale back from their projected 3000 peak sustained rpms for their V12.
Don't kill the messenger.
I think Porsche tried to develop a motor that shifted reliably at, say, 7500 rpms. This is hardly unreasonable for a company with a racing heritage developing a clean sheet OHC V8 in the late 1960s. They had to scale that expectation back. Just like Maybach had to scale back from their projected 3000 peak sustained rpms for their V12.
Don't kill the messenger.
You may be interested in a 7k rpm motor, but those running 928s on the track would likely be VERY satisfied with reliability at 6k motor.
So, if you want to help the audience here, then it can't be about what YOU want.
02-29-2008, 12:57 PM
#350
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02-29-2008, 01:10 PM
#351
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Speaking purely as an outsider looking in. I think this thread has touched on alot of usefull information for the entire community. I hope you guys can continue this discussion without getting angry at one another. I know its hard to do someimes, believe me , I do. 
Carry on.
Carry on.
02-29-2008, 01:31 PM
#352
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I think you have missed the point that the reliability issue you mentioned was solved two years ago for the 928 wet sump. That is for an engine in otherwise good condition, of course.
Certainly dry sumps will be needed when the performance on the track has sustained g-forces that stack the oil sideways. But you can calculate this border very simply. I believe it is the cotangent of theta -- theta being the angle of repose measured from the horizontal. Use your data logger to learn your lateral g-forces and compare. Fill your pan with measured water, get a level -- get a protractor.
I have done this for the 928 sump -- yes, the 928 engine that is the subject of this thread. Have you????? Surely you have, right?
The other thing you are missing is that all those other engines contain the knowledge and data accrued from the work of thousands of engineers over scores of years. Moreover, Porsche itself did the same sort of analysis -- that is why they tried to borrow the floor scraper design from the Ford FE that preceded it by a decade.
Certainly dry sumps will be needed when the performance on the track has sustained g-forces that stack the oil sideways. But you can calculate this border very simply. I believe it is the cotangent of theta -- theta being the angle of repose measured from the horizontal. Use your data logger to learn your lateral g-forces and compare. Fill your pan with measured water, get a level -- get a protractor.
I have done this for the 928 sump -- yes, the 928 engine that is the subject of this thread. Have you????? Surely you have, right?
The other thing you are missing is that all those other engines contain the knowledge and data accrued from the work of thousands of engineers over scores of years. Moreover, Porsche itself did the same sort of analysis -- that is why they tried to borrow the floor scraper design from the Ford FE that preceded it by a decade.
You do yourself no service at all by your posts in these threads. I would be very surprised to find that you generate more sales and or even simply respect by your posts.
02-29-2008, 01:59 PM
#353
Wait, what were we arguing about again?
02-29-2008, 04:49 PM
#354
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Wow, I hope people who are reading Kevin Johnson's 'expert opinion' on rod caps of motors realize that the crank scraper he designed and shipped to a customer (mtcarrera) wasn't even ballpark close. It had major contact issues and had to be modified to be installed. Just throwing that out there.
It has been established by a number of more reputable sources that the outside alignments of the rodcaps mean nothing and it has only to do with the inner surfaces. Why he keeps harping on such an improbably excuse that they were dropped and mixed up at the factory and the like is thoroughly beyond me. The numbers matched and had run with no issues for many many miles before the failure under DE conditions.
As for Hacker's questions about the mtcarrera motors. Neither were accusumped. The new motor will have a dry sump.
It has been established by a number of more reputable sources that the outside alignments of the rodcaps mean nothing and it has only to do with the inner surfaces. Why he keeps harping on such an improbably excuse that they were dropped and mixed up at the factory and the like is thoroughly beyond me. The numbers matched and had run with no issues for many many miles before the failure under DE conditions.
As for Hacker's questions about the mtcarrera motors. Neither were accusumped. The new motor will have a dry sump.
02-29-2008, 05:15 PM
#355
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If I've been keeping proper track, so far only one track motor has been lost due to an oil related issue that had an accusump.
It puzzles me why anyone would be on the track without one (or dry sump)
02-29-2008, 09:28 PM
#356
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Insulting those who disagree with you is similar ludicrous. Your argument is not enhanced, nor does it improve your status with regard to respect.
02-29-2008, 09:30 PM
#357
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JB, no it has not been so established. The more reputable sources claim many things but display little save assertions. On the other hand, I take actual Porsche parts and measure them and photograph them. I asked for these other reputable sources to produce just one counter-example. So far, nothing.
I quote current Porsche engine manufacturing processes and they support my theory. Imagine that.
You are just verbally gesticulating. Try some producing some modicum of hard empirical evidence. Please.
That simply shows you are unaware of what commonly goes on in manufacturing plants. So, you tell me why the factory needs to label the caps "944" and "928". Give me a break.
Dave did not have the rods resized -- he popped new bearings into them. If the original owner of the engine drove sanely, the original bearings with a mismatch of say, .001", might have worn gradually to minimize or eliminate any "step". Fresh bearings and tromping on the engine under DE conditions revealed the original problem -- my theory. This isn't rocket science.
You present a 'story' you make up and call it evidence and then you call me a sophomoric undergraduate.
02-29-2008, 09:33 PM
#358
Apart from the personal stuff going on here, I can attest to the vast difference in dimensions, both total and in various areas in the circumference, between a re-sized big end and one that was from a used engine. The rod accepted the bearings so differently than when I did the rod bearings on a garage basement floor with the engine in a car, that I will never go back.
Play through.
Play through.
02-29-2008, 09:48 PM
#359
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NO
They said they had evidence that would disprove it and then failed to produce it. GET IT STRAIGHT.
The evidence I have presented supports the theory. You are free to present your own. Please do so.
Who called who a fool ? Who labled the theory as "bullcrap"?
Wake up, Stan.
They said they had evidence that would disprove it and then failed to produce it. GET IT STRAIGHT.
The evidence I have presented supports the theory. You are free to present your own. Please do so.
Who called who a fool ? Who labled the theory as "bullcrap"?
Wake up, Stan.
A theory on what? Why 928 the crankshaft pictured in the first post failed? Why 928s commonly have 2/6 rod bearing failures? Why Dave C.'s motor failed even with the scraper? My theory would hold little weight as I don't have the motors to review, nor do I suggest I have the expertise to do so. All that I can provide is that I doubt your theory based on what I have seen and heard in the past as well as what you have posted here.
I doubt it was I that called you a fool or your theory as bull crap. I do definitely think you theory is far fetched and self serving. As I have said above, I do not find your "evidence" compelling. Doesn't seem like anyone else does either...
