Drilled Crank Thoughts...
06-26-2009, 02:14 PM
#526
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06-26-2009, 03:28 PM
#528
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01-11-2011, 04:41 AM
#531
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I'm just a poor dumb Chevy racer, but I'm amazed at the amount of energy and money you guys throw at this stuff. These are not big engines, or being revved that high, or making that much power.
The key point never mentioned is that the flow of oil through the bearing has to be sufficient to carry off the heat created by the load on the bearing. Insuficent flow leads to the oil flashing off (vaporizing) and there goes the lubricity. So the combination of oil viscosity, oil temperature, bearing clearance (including a side clearance greater than the rod bearing clearance so it's not a restriction to flow across the bearing), bearing load, and pump volume/pressure has to be carefully balanced. If you haven't miked the bearings and the crank yourself, you don't know what you have. A professional Sunnen dial bore gauge, a Starret machinists straight edge, and a set of Mitutoyo outside mikes will cost you less than $1500, and that's cheap given what you guys spend on one of these engines. You must really like these cars for some reason I don't get, or just like a really big challenge.
Given adequate oil system specs for sufficient flow for bearing cooling - and a plain bearing engine is one big controlled leak made up of lots of little ones - the next thing is to make sure the oil is supplied to the bearings in an unbroken supply, with no air, at a reasonable temperature. If the supply is interupted, the film will fail very quickly. And air has **** for lubricity, so entained air equals an interuption in the supply. If you you do everythign right with a wet sump system, you may get away with it. With a dry sump, you are measuring your oil supply in gallons, not quarts, it is inherently de-aerating, and cooler to boot, and you are evacuating the sump all the time so windage is greatly reduced in any case. That's why all real race engines, and most other Porsches, have at least a simple dry sump. It works. Do it. And use a big oil cooler. The engine is as much oil cooled as air cooled.
As far as the crank drilling, the feed from the main to the rod occurs when the feed hole in the main journal is lined up with the groove in the upper main bearing half. Unless the passage is "cross drilled" there is no active feed until the hole comes around again. So the point of cross drilling, at least Chevy style, is to provide 360 degree oil supply to the rod jounal. I have no idea why Porsche did it the way they did, and I don't care. I don't worship them, I respect results. And the simple Chevy pattern works. Period.
And no you don't want to do this with a "fully grooved main beraing" since you can't afford the loss of bearing area on the loaded bottom half.
And detonation will kill anything. Avoid.
The 928 apparently has a grossly deficient oiling system, despite how superficially sophisticated it appears. Contray to the German philosophy, complexity doesn't equal sophistication. Or performance. This is pathetic power and reliability. You can get any number of American V8s for half this that will make 750+ HP and live, despite their crude two valve pushrod design. Just buy a used Nascar engine, back it off to 8000 rpm, and go play.
Of course, your masochistic German worship will be thwarted, except for the shortcomings of the car itself. At that point why don't you just get a real Corvette instead of a fake one?
The truth hurts.
David Merritt
The key point never mentioned is that the flow of oil through the bearing has to be sufficient to carry off the heat created by the load on the bearing. Insuficent flow leads to the oil flashing off (vaporizing) and there goes the lubricity. So the combination of oil viscosity, oil temperature, bearing clearance (including a side clearance greater than the rod bearing clearance so it's not a restriction to flow across the bearing), bearing load, and pump volume/pressure has to be carefully balanced. If you haven't miked the bearings and the crank yourself, you don't know what you have. A professional Sunnen dial bore gauge, a Starret machinists straight edge, and a set of Mitutoyo outside mikes will cost you less than $1500, and that's cheap given what you guys spend on one of these engines. You must really like these cars for some reason I don't get, or just like a really big challenge.
Given adequate oil system specs for sufficient flow for bearing cooling - and a plain bearing engine is one big controlled leak made up of lots of little ones - the next thing is to make sure the oil is supplied to the bearings in an unbroken supply, with no air, at a reasonable temperature. If the supply is interupted, the film will fail very quickly. And air has **** for lubricity, so entained air equals an interuption in the supply. If you you do everythign right with a wet sump system, you may get away with it. With a dry sump, you are measuring your oil supply in gallons, not quarts, it is inherently de-aerating, and cooler to boot, and you are evacuating the sump all the time so windage is greatly reduced in any case. That's why all real race engines, and most other Porsches, have at least a simple dry sump. It works. Do it. And use a big oil cooler. The engine is as much oil cooled as air cooled.
As far as the crank drilling, the feed from the main to the rod occurs when the feed hole in the main journal is lined up with the groove in the upper main bearing half. Unless the passage is "cross drilled" there is no active feed until the hole comes around again. So the point of cross drilling, at least Chevy style, is to provide 360 degree oil supply to the rod jounal. I have no idea why Porsche did it the way they did, and I don't care. I don't worship them, I respect results. And the simple Chevy pattern works. Period.
And no you don't want to do this with a "fully grooved main beraing" since you can't afford the loss of bearing area on the loaded bottom half.
And detonation will kill anything. Avoid.
The 928 apparently has a grossly deficient oiling system, despite how superficially sophisticated it appears. Contray to the German philosophy, complexity doesn't equal sophistication. Or performance. This is pathetic power and reliability. You can get any number of American V8s for half this that will make 750+ HP and live, despite their crude two valve pushrod design. Just buy a used Nascar engine, back it off to 8000 rpm, and go play.
Of course, your masochistic German worship will be thwarted, except for the shortcomings of the car itself. At that point why don't you just get a real Corvette instead of a fake one?
The truth hurts.
David Merritt
01-11-2011, 06:02 AM
#532
O.K I'll bite, firstly I give you most of the facts you state, if you want a read this is my position on the topic. More detailed than my response below.
https://rennlist.com/forums/928-foru...nd-oiling.html
The 928 engine can be quite powerful and believe can be oiled quite successfully at higher revs, say 8,500. The engine needs dry sumping, it has a very shallow sump due to the installation required in the car. So combine that with some ill devised ideas, the Porsche oil pump supplies 3 times the amount of oil that a Nascar engine does.
I for one agree with your main bearing analogy and bought 3 sets of the no longer available plain or non grooved main bearings. As you say fully grooved can't support the loads in the engine.
The car itself it a very stylish car that has some classic design features, it had a number of technical firsts and when upgraded, which I regard as fun can match pretty much anything.
A used Nascar engine is not comparing apples to apples, someone else has poured a fortune into it in R&D and parts, you then buy that on the cheap, you just can't do that with a 928, much smaller market.
Greg
P.S in this dry sumping thread, I am fabricating a carbon oil tanks used in conjunction with a 6 stage Auto Verdi.
https://rennlist.com/forums/928-foru...umping-12.html
https://rennlist.com/forums/928-foru...nd-oiling.html
The 928 engine can be quite powerful and believe can be oiled quite successfully at higher revs, say 8,500. The engine needs dry sumping, it has a very shallow sump due to the installation required in the car. So combine that with some ill devised ideas, the Porsche oil pump supplies 3 times the amount of oil that a Nascar engine does.
I for one agree with your main bearing analogy and bought 3 sets of the no longer available plain or non grooved main bearings. As you say fully grooved can't support the loads in the engine.
The car itself it a very stylish car that has some classic design features, it had a number of technical firsts and when upgraded, which I regard as fun can match pretty much anything.
A used Nascar engine is not comparing apples to apples, someone else has poured a fortune into it in R&D and parts, you then buy that on the cheap, you just can't do that with a 928, much smaller market.
Greg
P.S in this dry sumping thread, I am fabricating a carbon oil tanks used in conjunction with a 6 stage Auto Verdi.
https://rennlist.com/forums/928-foru...umping-12.html
01-11-2011, 06:12 AM
#533
Nordschleife Master
I am feeling no pain, but despite that agree with a lot of what you say, OTOH I know I don't know much. Could be aeration is the root problem.
OTOH I am starting to think some 911 engineer added a few "features" to make the 911 a little safer from the 928 on the track.
OTOH I am starting to think some 911 engineer added a few "features" to make the 911 a little safer from the 928 on the track.
01-11-2011, 07:36 AM
#534
Rennlist Member
Just a thought when I saw this old thread.
When I had my 944 Turbo there was a lot of similar ideas being discussed and implemented to try to solve the similar bearing failure at high rpm/g loading on the 944 Turbo motor. And most with similar hit and miss outcomes. One of the things discussed caught my interest and I don't think I saw or read about in this thread. It had to do with the oil galleys feeding the crank and it wasn't the relative size in relation to the bearing being fed. Instead it had to do with the placement of the oil feed for the galley itself and the flow characteristics in the galley based on that feed point and the delivery points for each bearing. Someone actually modeled the galley in a fluid dynamics software program and found the model duplicated the same oil starvation problem. Enlarging the galley ports into the problem bearings helped a little but did not solve the low flow problem. However, changing location of the feed point into the galley did. The proposed solution was to plug the stock feed into the galley and pump the oil in from both ends of the galley. Never actually saw it implemented though.
When I had my 944 Turbo there was a lot of similar ideas being discussed and implemented to try to solve the similar bearing failure at high rpm/g loading on the 944 Turbo motor. And most with similar hit and miss outcomes. One of the things discussed caught my interest and I don't think I saw or read about in this thread. It had to do with the oil galleys feeding the crank and it wasn't the relative size in relation to the bearing being fed. Instead it had to do with the placement of the oil feed for the galley itself and the flow characteristics in the galley based on that feed point and the delivery points for each bearing. Someone actually modeled the galley in a fluid dynamics software program and found the model duplicated the same oil starvation problem. Enlarging the galley ports into the problem bearings helped a little but did not solve the low flow problem. However, changing location of the feed point into the galley did. The proposed solution was to plug the stock feed into the galley and pump the oil in from both ends of the galley. Never actually saw it implemented though.
01-11-2011, 10:20 AM
#536
Nordschleife Master
I do wonder about your angry closing thoughts.
It's about having fun. These are awesomely cool cars and the price-point is sweet. I've got a lot into mine but still a lot less than any corvette that surpasses its performance.
If we're "idiots" then we're happy idiots and the best parts of life aren't logical.
01-11-2011, 10:40 AM
#537
Not the sharpest tool in the shed
Rennlist Member
Rennlist Member
What was your intent when you posted this? Why are you here? Strange first post.
I'm just a poor dumb Chevy racer, but I'm amazed at the amount of energy and money you guys throw at this stuff. These are not big engines, or being revved that high, or making that much power.
The key point never mentioned is that the flow of oil through the bearing has to be sufficient to carry off the heat created by the load on the bearing. Insuficent flow leads to the oil flashing off (vaporizing) and there goes the lubricity. So the combination of oil viscosity, oil temperature, bearing clearance (including a side clearance greater than the rod bearing clearance so it's not a restriction to flow across the bearing), bearing load, and pump volume/pressure has to be carefully balanced. If you haven't miked the bearings and the crank yourself, you don't know what you have. A professional Sunnen dial bore gauge, a Starret machinists straight edge, and a set of Mitutoyo outside mikes will cost you less than $1500, and that's cheap given what you guys spend on one of these engines. You must really like these cars for some reason I don't get, or just like a really big challenge.
Given adequate oil system specs for sufficient flow for bearing cooling - and a plain bearing engine is one big controlled leak made up of lots of little ones - the next thing is to make sure the oil is supplied to the bearings in an unbroken supply, with no air, at a reasonable temperature. If the supply is interupted, the film will fail very quickly. And air has **** for lubricity, so entained air equals an interuption in the supply. If you you do everythign right with a wet sump system, you may get away with it. With a dry sump, you are measuring your oil supply in gallons, not quarts, it is inherently de-aerating, and cooler to boot, and you are evacuating the sump all the time so windage is greatly reduced in any case. That's why all real race engines, and most other Porsches, have at least a simple dry sump. It works. Do it. And use a big oil cooler. The engine is as much oil cooled as air cooled.
As far as the crank drilling, the feed from the main to the rod occurs when the feed hole in the main journal is lined up with the groove in the upper main bearing half. Unless the passage is "cross drilled" there is no active feed until the hole comes around again. So the point of cross drilling, at least Chevy style, is to provide 360 degree oil supply to the rod jounal. I have no idea why Porsche did it the way they did, and I don't care. I don't worship them, I respect results. And the simple Chevy pattern works. Period.
And no you don't want to do this with a "fully grooved main beraing" since you can't afford the loss of bearing area on the loaded bottom half.
And detonation will kill anything. Avoid.
The 928 apparently has a grossly deficient oiling system, despite how superficially sophisticated it appears. Contray to the German philosophy, complexity doesn't equal sophistication. Or performance. This is pathetic power and reliability. You can get any number of American V8s for half this that will make 750+ HP and live, despite their crude two valve pushrod design. Just buy a used Nascar engine, back it off to 8000 rpm, and go play.
Of course, your masochistic German worship will be thwarted, except for the shortcomings of the car itself. At that point why don't you just get a real Corvette instead of a fake one?
The truth hurts.
David Merritt
The key point never mentioned is that the flow of oil through the bearing has to be sufficient to carry off the heat created by the load on the bearing. Insuficent flow leads to the oil flashing off (vaporizing) and there goes the lubricity. So the combination of oil viscosity, oil temperature, bearing clearance (including a side clearance greater than the rod bearing clearance so it's not a restriction to flow across the bearing), bearing load, and pump volume/pressure has to be carefully balanced. If you haven't miked the bearings and the crank yourself, you don't know what you have. A professional Sunnen dial bore gauge, a Starret machinists straight edge, and a set of Mitutoyo outside mikes will cost you less than $1500, and that's cheap given what you guys spend on one of these engines. You must really like these cars for some reason I don't get, or just like a really big challenge.
Given adequate oil system specs for sufficient flow for bearing cooling - and a plain bearing engine is one big controlled leak made up of lots of little ones - the next thing is to make sure the oil is supplied to the bearings in an unbroken supply, with no air, at a reasonable temperature. If the supply is interupted, the film will fail very quickly. And air has **** for lubricity, so entained air equals an interuption in the supply. If you you do everythign right with a wet sump system, you may get away with it. With a dry sump, you are measuring your oil supply in gallons, not quarts, it is inherently de-aerating, and cooler to boot, and you are evacuating the sump all the time so windage is greatly reduced in any case. That's why all real race engines, and most other Porsches, have at least a simple dry sump. It works. Do it. And use a big oil cooler. The engine is as much oil cooled as air cooled.
As far as the crank drilling, the feed from the main to the rod occurs when the feed hole in the main journal is lined up with the groove in the upper main bearing half. Unless the passage is "cross drilled" there is no active feed until the hole comes around again. So the point of cross drilling, at least Chevy style, is to provide 360 degree oil supply to the rod jounal. I have no idea why Porsche did it the way they did, and I don't care. I don't worship them, I respect results. And the simple Chevy pattern works. Period.
And no you don't want to do this with a "fully grooved main beraing" since you can't afford the loss of bearing area on the loaded bottom half.
And detonation will kill anything. Avoid.
The 928 apparently has a grossly deficient oiling system, despite how superficially sophisticated it appears. Contray to the German philosophy, complexity doesn't equal sophistication. Or performance. This is pathetic power and reliability. You can get any number of American V8s for half this that will make 750+ HP and live, despite their crude two valve pushrod design. Just buy a used Nascar engine, back it off to 8000 rpm, and go play.
Of course, your masochistic German worship will be thwarted, except for the shortcomings of the car itself. At that point why don't you just get a real Corvette instead of a fake one?
The truth hurts.
David Merritt
01-11-2011, 10:53 AM
#538
Addict
Rennlist Member
Rennlist Member
01-11-2011, 01:31 PM
#539
Addict
Lifetime Rennlist
Member
Lifetime Rennlist
Member
Tractor flywheels are HUGE that makes them run very smooth and pull well just not accelerate. Kinda like a 928 with it's heavy crank flywheel and clutch package. Buying used NASCAR engines is pretty silly since they are timed out , at the end of the designed life cycle and ready to fail. Especially given the lack of roller cams etc. and that they are designed to run 7,000-9,000 RPM they would be horrible for a street engine. But thanks for the post.
with it's heavy crank flywheel and clutch package. Buying used NASCAR engines is pretty silly since they are timed out , at the end of the designed life cycle and ready to fail. Especially given the lack of roller cams etc. and that they are designed to run 7,000-9,000 RPM they would be horrible for a street engine. But thanks for the post.
01-11-2011, 01:39 PM
#540
Rennlist Member
David, I agree, there is a lot of agoney here for an engine that isnt running too high of RPM and not making nascar power. BUT, i have more race days with a stock 928 engine than anyone here, by far, and I have never had any issues. (could be the amsoil, how I warm it up, the tracks i visit, how i drive, i dont know, but those who do what I do have the same luck. 
)
Ive raced against the built mustangs and Vets. go watch my videos of how they do. what you cant see are ALL the problems they have in the pits or on the track, BLOWING motors, or having all sorts of issues. my car, with its original engine of 25 years old, ran 107 race days, and I only pulled it out to put in the stroker. It has lasted near 3 seasons so far, oil analysis says its running well, and its posting times at laguna faster (Ive run 1:36.1 at laguna seca on DOT race rubber) than ANY porsche GT3 street car on DOT race rubber, with any pro driver in it. (several have tested there at times much slower, i.e. Angelleli, Pobst, and a couple of others) Ive even run against one of the top porsche race teams in their completely race ready GT3 street to race conversion, and won. So, I ask you , can you do this with ANY corvette that is over 4-5years old??? That is the point. No mods at all, no computer, intake, oiling, venting, sumping, baffling, timing, sparkplug wire, nothing nothing nothing. just a set of headers and a bolt on suspension, which is by the way, over 15 years old now too! THIS is why we like the car. it can do things better and much more reliable than ANY of the other cars I see at the track. And I'll give you a boat load of stories of the top pro prepared and private nut case teams I race against that have had HUGE issues over the years, while I mostly beat them, drive the car to the track and drive the car home, WITHOUT touching a bolt on the car , usually ever a the track.
These are the guys.
camaro. evolving to a near nascar motor and trimec trasmission . LOADS of engines, transmission problems. finally, dropped an LS7 in there. $$$$
S2000 500rwhp blowing engines. no surprise, but really fast
M3 PTG copy. blowing rear ends, power issues, running issues, sometimes just dead
C5 corvette, WCGT modifications. pretty dependable , only 2 engines blown or major issues. overall, my closest competitor when I was stockish.
RX7 turbo with Vet engine LS1 transplant. very fast, blown engine
comp coupe vipers! very fast, run through a lot of tires, near as fast, generally pretty dependable. downside, factory race car at near $100k per copy
M3 e36 with euro 3.2 and intake mods. also very dependable and fast, but not quite as fast, and certainly needs a little tweaking to make fast, with body structure, engine managment, and very expensive suspension set ups.
Mustang with 500hp RV motor. low rev, high torque, but a LOT of work to build. very dependable, but still many problems like head gaskets, and other problems that most US cars seem to have over time. not a lot of hours racing before some major issues.
very fast near NASCAR powered mustang. the fastest out there. very expensive to run and tune. never running quite right and blowing through transmissions. (expensive Dog gear types)
anyway, these are the guys I run with , they all have issues, yet, I show up, give most of these cars a race or beat them and I drive my rig home and do a lot of street drving too. try that with your Corvette that you seem to think is a much better choise for us silly 928 owners.
As glen said, its a bang for the buck thing, and when you get a 928 dialed in, it is like no other super car. really a comfortable , well driving car and it does have a unique sporty look for an old dog. heck, look at mine. its a 1987!
wanna race?????
Mk
) Ive raced against the built mustangs and Vets. go watch my videos of how they do. what you cant see are ALL the problems they have in the pits or on the track, BLOWING motors, or having all sorts of issues. my car, with its original engine of 25 years old, ran 107 race days, and I only pulled it out to put in the stroker. It has lasted near 3 seasons so far, oil analysis says its running well, and its posting times at laguna faster (Ive run 1:36.1 at laguna seca on DOT race rubber) than ANY porsche GT3 street car on DOT race rubber, with any pro driver in it. (several have tested there at times much slower, i.e. Angelleli, Pobst, and a couple of others) Ive even run against one of the top porsche race teams in their completely race ready GT3 street to race conversion, and won. So, I ask you , can you do this with ANY corvette that is over 4-5years old??? That is the point. No mods at all, no computer, intake, oiling, venting, sumping, baffling, timing, sparkplug wire, nothing nothing nothing. just a set of headers and a bolt on suspension, which is by the way, over 15 years old now too!
THIS is why we like the car. it can do things better and much more reliable than ANY of the other cars I see at the track. And I'll give you a boat load of stories of the top pro prepared and private nut case teams I race against that have had HUGE issues over the years, while I mostly beat them, drive the car to the track and drive the car home, WITHOUT touching a bolt on the car , usually ever a the track. These are the guys.
camaro. evolving to a near nascar motor and trimec trasmission . LOADS of engines, transmission problems. finally, dropped an LS7 in there.
$$$$S2000 500rwhp blowing engines. no surprise, but really fast
M3 PTG copy. blowing rear ends, power issues, running issues, sometimes just dead
C5 corvette, WCGT modifications. pretty dependable , only 2 engines blown or major issues. overall, my closest competitor when I was stockish.
RX7 turbo with Vet engine LS1 transplant. very fast, blown engine
comp coupe vipers! very fast, run through a lot of tires, near as fast, generally pretty dependable. downside, factory race car at near $100k per copy
M3 e36 with euro 3.2 and intake mods. also very dependable and fast, but not quite as fast, and certainly needs a little tweaking to make fast, with body structure, engine managment, and very expensive suspension set ups.
Mustang with 500hp RV motor. low rev, high torque, but a LOT of work to build. very dependable, but still many problems like head gaskets, and other problems that most US cars seem to have over time. not a lot of hours racing before some major issues.
very fast near NASCAR powered mustang. the fastest out there. very expensive to run and tune. never running quite right and blowing through transmissions. (expensive Dog gear types)
anyway, these are the guys I run with , they all have issues, yet, I show up, give most of these cars a race or beat them and I drive my rig home and do a lot of street drving too. try that with your Corvette that you seem to think is a much better choise for us silly 928 owners.
As glen said, its a bang for the buck thing, and when you get a 928 dialed in, it is like no other super car. really a comfortable , well driving car and it does have a unique sporty look for an old dog. heck, look at mine. its a 1987!
wanna race?????
Mk
I'm just a poor dumb Chevy racer, but I'm amazed at the amount of energy and money you guys throw at this stuff. These are not big engines, or being revved that high, or making that much power.
The key point never mentioned is that the flow of oil through the bearing has to be sufficient to carry off the heat created by the load on the bearing. Insuficent flow leads to the oil flashing off (vaporizing) and there goes the lubricity. So the combination of oil viscosity, oil temperature, bearing clearance (including a side clearance greater than the rod bearing clearance so it's not a restriction to flow across the bearing), bearing load, and pump volume/pressure has to be carefully balanced. If you haven't miked the bearings and the crank yourself, you don't know what you have. A professional Sunnen dial bore gauge, a Starret machinists straight edge, and a set of Mitutoyo outside mikes will cost you less than $1500, and that's cheap given what you guys spend on one of these engines. You must really like these cars for some reason I don't get, or just like a really big challenge.
Given adequate oil system specs for sufficient flow for bearing cooling - and a plain bearing engine is one big controlled leak made up of lots of little ones - the next thing is to make sure the oil is supplied to the bearings in an unbroken supply, with no air, at a reasonable temperature. If the supply is interupted, the film will fail very quickly. And air has **** for lubricity, so entained air equals an interuption in the supply. If you you do everythign right with a wet sump system, you may get away with it. With a dry sump, you are measuring your oil supply in gallons, not quarts, it is inherently de-aerating, and cooler to boot, and you are evacuating the sump all the time so windage is greatly reduced in any case. That's why all real race engines, and most other Porsches, have at least a simple dry sump. It works. Do it. And use a big oil cooler. The engine is as much oil cooled as air cooled.
As far as the crank drilling, the feed from the main to the rod occurs when the feed hole in the main journal is lined up with the groove in the upper main bearing half. Unless the passage is "cross drilled" there is no active feed until the hole comes around again. So the point of cross drilling, at least Chevy style, is to provide 360 degree oil supply to the rod jounal. I have no idea why Porsche did it the way they did, and I don't care. I don't worship them, I respect results. And the simple Chevy pattern works. Period.
And no you don't want to do this with a "fully grooved main beraing" since you can't afford the loss of bearing area on the loaded bottom half.
And detonation will kill anything. Avoid.
The 928 apparently has a grossly deficient oiling system, despite how superficially sophisticated it appears. Contray to the German philosophy, complexity doesn't equal sophistication. Or performance. This is pathetic power and reliability. You can get any number of American V8s for half this that will make 750+ HP and live, despite their crude two valve pushrod design. Just buy a used Nascar engine, back it off to 8000 rpm, and go play.
Of course, your masochistic German worship will be thwarted, except for the shortcomings of the car itself. At that point why don't you just get a real Corvette instead of a fake one?
The truth hurts.
David Merritt
The key point never mentioned is that the flow of oil through the bearing has to be sufficient to carry off the heat created by the load on the bearing. Insuficent flow leads to the oil flashing off (vaporizing) and there goes the lubricity. So the combination of oil viscosity, oil temperature, bearing clearance (including a side clearance greater than the rod bearing clearance so it's not a restriction to flow across the bearing), bearing load, and pump volume/pressure has to be carefully balanced. If you haven't miked the bearings and the crank yourself, you don't know what you have. A professional Sunnen dial bore gauge, a Starret machinists straight edge, and a set of Mitutoyo outside mikes will cost you less than $1500, and that's cheap given what you guys spend on one of these engines. You must really like these cars for some reason I don't get, or just like a really big challenge.
Given adequate oil system specs for sufficient flow for bearing cooling - and a plain bearing engine is one big controlled leak made up of lots of little ones - the next thing is to make sure the oil is supplied to the bearings in an unbroken supply, with no air, at a reasonable temperature. If the supply is interupted, the film will fail very quickly. And air has **** for lubricity, so entained air equals an interuption in the supply. If you you do everythign right with a wet sump system, you may get away with it. With a dry sump, you are measuring your oil supply in gallons, not quarts, it is inherently de-aerating, and cooler to boot, and you are evacuating the sump all the time so windage is greatly reduced in any case. That's why all real race engines, and most other Porsches, have at least a simple dry sump. It works. Do it. And use a big oil cooler. The engine is as much oil cooled as air cooled.
As far as the crank drilling, the feed from the main to the rod occurs when the feed hole in the main journal is lined up with the groove in the upper main bearing half. Unless the passage is "cross drilled" there is no active feed until the hole comes around again. So the point of cross drilling, at least Chevy style, is to provide 360 degree oil supply to the rod jounal. I have no idea why Porsche did it the way they did, and I don't care. I don't worship them, I respect results. And the simple Chevy pattern works. Period.
And no you don't want to do this with a "fully grooved main beraing" since you can't afford the loss of bearing area on the loaded bottom half.
And detonation will kill anything. Avoid.
The 928 apparently has a grossly deficient oiling system, despite how superficially sophisticated it appears. Contray to the German philosophy, complexity doesn't equal sophistication. Or performance. This is pathetic power and reliability. You can get any number of American V8s for half this that will make 750+ HP and live, despite their crude two valve pushrod design. Just buy a used Nascar engine, back it off to 8000 rpm, and go play.
Of course, your masochistic German worship will be thwarted, except for the shortcomings of the car itself. At that point why don't you just get a real Corvette instead of a fake one?
The truth hurts.
David Merritt