Crank, bottom end design, friction and oiling
10-27-2009, 08:26 AM
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Crank, bottom end design, friction and oiling
I have been doing some research about our cranks and cranks in general. It is a complicated topic I don't know all the answers but I hope that we can discuss the facts and possibilities. As you know I have always liked the high revving engines. That comes about because of factors, I like the manuals and the engine can be a smaller displacement as such a bit more economical and most important factor is the high revving aspect means that it places less strain on its drivetrain components. The engine has to rely on the fact that it has been built to be efficient.
One of the things I investigated earlier was the Honda rod journals, I have that on my Moldex crank, the criticism I have seen about these smaller journals is that they may not be able to handle detonation? I must admit I don't know, there is a decent choice of bearings available they are eccentric and as the rods are stronger and have greater hoop strength plus they need less oil as the diameter is a lot smaller and this allows a greater bearing clearance which is needed for an engine to run higher revs.
Even Porsche's venerable GT3 racing engine is having its journals resized recently. The other crank factor is the main bearing resizing, this is done all the time in performance engines. The crank below is a state of the art crank that can handle 850 hp and weighs 35 pounds, I spoke to the maker of the crank and they said they are happy to make 928 cranks but would be able to do a decent price if three were ordered which is fair enough.
In its rightful pace. The wife approves, in fact she bought it for me
The crank, if ordered will not be polished on all journals like the one above and probably made from a slightly different material. I was told around $3,500 and that would mean a crank that is lighter and stronger than what is presently offered. They told me do not confuse weight with strength. The weight difference being around 10 kgs or 22 pounds lighter than current offerings. That is a lot of weight especially when it is spinning and coming from the front end. All that heavy metal actually makes the crank lighter in the end.
Now this is only for manual cars and ones that don't need smog checks etc, there would be no point in anything but an all out application and I am not suggesting anybody that has the current crank they do anything but drive their cars but if you are about to set out on a project you may find this interesting. I have also included some information on friction and oils
This is what the bushed down mains look like.
The crank maker suggests to use a 2.3" or 2.5" mains, if the 2.3 mains are used the RO7 bearings are probably a perfect candidate, the reason is that the RO7 engine's crank looks very similar to our 928 8 counter weight stroker cranks.
Here's a Moldex crank, see how similar they are, (not my pic, I'll remove it if need be)
There is a reason that the new engines are using centre main bearings, they have a greater stiffness and this helps to reduce centre main bending deflection.
The reason to use 8 counter weight cranks is power and strength, there has been studies done that prove a greater power is produced with these cranks and they have better reliability. Most crank makers at the top of their field agree with this also. The reason for for the difference is the measurable losses that occur with 6 counter weight cranks at high rpm high power applications. Bending deflection is the cause for the deflection and as such it makes sense that the extra weights provide better balance and less stress.
There is also some investigation going on in relation to how to oil the crank and the rods as mains 2 and 4 are the most highly stressed in a 2 plane V8 crank. There is some makers that drilled the crank in a way similar to the 928 crank, don't laugh just yet.
What they are doing is allowing the mains 2 and 4 just to oil themselves and not supply and oil to the rods. The oiling to the rods is supplied by 1,3,and 5 and drilled in a way that there is cross drilling and because of the crossecting drillings there is a need in high power applications that the internal drilling need de-stressing, this is done by extrude honing. Another advantage is that the oil hole that supplies the rod is perpendicular to the journal surface.
This is better than the straight shot oiling for oil support purposes. Bigger oil outlets do not support better contrary to some opinions. This is similar to grooved main bearings to plain main bearings, grooved mains are of course used for better oiling to the rods. However load bearing capacity drops dramatically and degrades the load carrying capacity and increases frictional losses. Even the use of half grooved main bearings is not used in very high revving engines.
In an engine such as a F1 they feed the mains but the mains do not feed the rods. The rods are feed from the nose bearing at the front of the crank. They use the nose feed because the oil pressure was consuming too much power as the revs rose. In an article I saw there was an engine was switched from oiling the rods from the mains to nose feed and the oil pressure was able to dropped by 1 bar to 5 bar.
A friend of mine said to me that the oiling to the rods was supplied by the centrifugal force, that is after it has overcome the centrifugal force to get to the centre of the crank if I understood him correctly.
The smaller mains will allow a lower oil pressure due to the fact that the oil doesn't have to overcome so much centrifugal force. The lesser bearing speed also means less friction, this comes more into play at high revs. Now with lighter rods and journals that are swinging from the centreline of the crank, this means less centrifugal loading on the cranks rod journals and bearings.
The other part of this work is getting the oiling right, in an article written by Jack Kane and Ian Bamsey, there is three modes that the bearings operate in, fully hydrodynamic, boundary and mixed.
Bearing friction is measured and valued by the equation of "Bearing Operating Condition" (BOC) BOC = Viscosity x RPM x K/Load The K is the factor that converts RPM and diameter into journal speed. (Which is why there is a gain from smaller journals) To me this formula is a bit counter intuitive, the reason I say this is is, with a greater load the friction is lowered to a point but it is always lower than boundary.
So with the use of smaller mains the load is proportionally increased, this helps the bottom number in the division by making it a larger number, the top number is made smaller by the fact as mentioned earlier the K factor. So it is win win in regards to friction. While friction is reduced due to lower viscosity oils, I wouldn't go there, some Nascar Teams still use 20W-50 and that is where I will stay unless there is a need for a 60 weight oil which some race cars use.
While doing my research for this topic I dug up this info from the SAE.
http://www.sae.org/events/pfs/presen...2005spikes.pdf
On page 46 there is the conclusion to a wear study that was conducted and the basis of the study was ZDDP and its effects. Now this might explain something that is important to all of us.
That is why some oils have caused high wear or maybe put another way allowed high wear. So oils that are not high in ZDDP may be doing more damage than oils with none! This may explain problems seen with Mobil 1. Various grades of Mobil 1 have different formulations.Another Rennlister JET951 may like to expand on this is his area given that he rebuilds these engines. Also if I understood it correctly there is increased friction when there is mixed lubrication when ZDDP is used. Maybe this is a by product of the mechanism of action? That is the protection offered slightly increases the friction.
There is some other issues that may be of interest, I will try to explain the terminology as best I can so that it makes sense, I have condensed the article so that if you have a question please ask it.
Back to the types of lubrication, boundary lube. is when there is a few molecules of oil between the sliding surfaces and the peaks of each surface touch each other. This is the highest friction and occurs on cold start up, a hydrodynamic wedge forms as the journal rotates and the oil is trapped. There is little pressures on the edges as the pressure escapes and peak pressure is in the centre of the bearing.
This is why grooved bearings cannot carry anywhere near the same load, (If a pic is desired i can draw it but the article and photos are copyright protected) if the bearing was wide enough pressure would peak and be level in the centre. I think that Porsche when they made this change, were just worried about the damage to the rod bearings that was happening in the marketplace and tried this as a fix not because it was better.
The film thickness may only be around 0.0001" but the pressure may be as high as 6,000 psi. Hydrodynamic pressure has nothing to do with engine oil pressure, the only relationship will be is there enough oil to cool the bearings and keep the hydrodynamic wedge going. Also the opening out of the oil galleries on the rod journals is bad for the same reasons. The opening needs to be kept small with only a small radius to relieve any stress.
The third mode is mixed, that is part hydrodynamic and part boundary. It is the transition between the two types of lubrication. There is a another type of lube that is not applicable to fluid film bearings and that is squeeze film. It is the type of lubrication that is seen in wrist or piston pins.
A bit of terminology, bearing eccentricity, I normally associated this with rod bearings, however it is also associated with the lubrication modes. Bearing eccentricity is the journal displacement from the centreline of the housing. That is off to one side, the journal does start to climb the wall of the journal as the journal or shaft starts turning.
An example may be, the mains or rods may have a 0.003" clearance. Or a radial clearance of 0.0015" and is operating with a oil film thickness of 0.0001". The sum would be (0.0015 - 0.0001)/0.0015= 0.9333" The actual shaft/journal diameter was not supplied in the article so that was not that helpful.
Looking at the Stribeck graph it shows that the friction starts off very high and as the journal starts to turn the hydrodynamic pressure starts to build and take over from the boundary lube. If rpm stays fixed and either viscosity decreases or unit load increases it will eventually reach its low point of friction of a BOC of 35. That value put into perspective is half the friction of a deep groove ball bearing.
If the loading continues to go up and or the viscosity decreases the BOC will move into the mixed lube mode where there is minor metal to metal contact. If this happens you have too low a viscosity oil or your bearings are too narrow.
I believe one of the reasons the crank that I have that looks like a mirror is polished in that way, is that they are are trying to keep those peaks and valleys to an absolute minimum to reduce this mixed lubrication.
From the low point of BOC 35 it only goes one way, if higher revs or higher viscosity or lower unit load, the friction rises exponentially or to approx ten times the low point. This is why much attention is paid to getting this right. Designers need to maintain the 35 to 50 BOC range.
So to sum up, when you change the mains and or rod journals to a smaller diameter, the unit load increases and the bearing speed decreases, two good things for lowering mechanical losses. I put this forward as some research to be discussed to hopefully move our engines forward. If anybody wants to contact me off list about a potential future crank order they can at ggray1964 at yahoo dot com I believe it needs more research and that will take time but I am in no hurry at present.
Otherwise happy to kick it around here for a while, there is a few more things to add but the wife wants me off the computer as we are on holidays
Cheers Greg
One of the things I investigated earlier was the Honda rod journals, I have that on my Moldex crank, the criticism I have seen about these smaller journals is that they may not be able to handle detonation? I must admit I don't know, there is a decent choice of bearings available they are eccentric and as the rods are stronger and have greater hoop strength plus they need less oil as the diameter is a lot smaller and this allows a greater bearing clearance which is needed for an engine to run higher revs.
Even Porsche's venerable GT3 racing engine is having its journals resized recently. The other crank factor is the main bearing resizing, this is done all the time in performance engines. The crank below is a state of the art crank that can handle 850 hp and weighs 35 pounds, I spoke to the maker of the crank and they said they are happy to make 928 cranks but would be able to do a decent price if three were ordered which is fair enough.
In its rightful pace. The wife approves, in fact she bought it for me
The crank, if ordered will not be polished on all journals like the one above and probably made from a slightly different material. I was told around $3,500 and that would mean a crank that is lighter and stronger than what is presently offered. They told me do not confuse weight with strength. The weight difference being around 10 kgs or 22 pounds lighter than current offerings. That is a lot of weight especially when it is spinning and coming from the front end. All that heavy metal actually makes the crank lighter in the end.
Now this is only for manual cars and ones that don't need smog checks etc, there would be no point in anything but an all out application and I am not suggesting anybody that has the current crank they do anything but drive their cars but if you are about to set out on a project you may find this interesting. I have also included some information on friction and oils
This is what the bushed down mains look like.
The crank maker suggests to use a 2.3" or 2.5" mains, if the 2.3 mains are used the RO7 bearings are probably a perfect candidate, the reason is that the RO7 engine's crank looks very similar to our 928 8 counter weight stroker cranks.
Here's a Moldex crank, see how similar they are, (not my pic, I'll remove it if need be)
There is a reason that the new engines are using centre main bearings, they have a greater stiffness and this helps to reduce centre main bending deflection.
The reason to use 8 counter weight cranks is power and strength, there has been studies done that prove a greater power is produced with these cranks and they have better reliability. Most crank makers at the top of their field agree with this also. The reason for for the difference is the measurable losses that occur with 6 counter weight cranks at high rpm high power applications. Bending deflection is the cause for the deflection and as such it makes sense that the extra weights provide better balance and less stress.
There is also some investigation going on in relation to how to oil the crank and the rods as mains 2 and 4 are the most highly stressed in a 2 plane V8 crank. There is some makers that drilled the crank in a way similar to the 928 crank, don't laugh just yet.
What they are doing is allowing the mains 2 and 4 just to oil themselves and not supply and oil to the rods. The oiling to the rods is supplied by 1,3,and 5 and drilled in a way that there is cross drilling and because of the crossecting drillings there is a need in high power applications that the internal drilling need de-stressing, this is done by extrude honing. Another advantage is that the oil hole that supplies the rod is perpendicular to the journal surface.
This is better than the straight shot oiling for oil support purposes. Bigger oil outlets do not support better contrary to some opinions. This is similar to grooved main bearings to plain main bearings, grooved mains are of course used for better oiling to the rods. However load bearing capacity drops dramatically and degrades the load carrying capacity and increases frictional losses. Even the use of half grooved main bearings is not used in very high revving engines.
In an engine such as a F1 they feed the mains but the mains do not feed the rods. The rods are feed from the nose bearing at the front of the crank. They use the nose feed because the oil pressure was consuming too much power as the revs rose. In an article I saw there was an engine was switched from oiling the rods from the mains to nose feed and the oil pressure was able to dropped by 1 bar to 5 bar.
A friend of mine said to me that the oiling to the rods was supplied by the centrifugal force, that is after it has overcome the centrifugal force to get to the centre of the crank if I understood him correctly.
The smaller mains will allow a lower oil pressure due to the fact that the oil doesn't have to overcome so much centrifugal force. The lesser bearing speed also means less friction, this comes more into play at high revs. Now with lighter rods and journals that are swinging from the centreline of the crank, this means less centrifugal loading on the cranks rod journals and bearings.
The other part of this work is getting the oiling right, in an article written by Jack Kane and Ian Bamsey, there is three modes that the bearings operate in, fully hydrodynamic, boundary and mixed.
Bearing friction is measured and valued by the equation of "Bearing Operating Condition" (BOC) BOC = Viscosity x RPM x K/Load The K is the factor that converts RPM and diameter into journal speed. (Which is why there is a gain from smaller journals) To me this formula is a bit counter intuitive, the reason I say this is is, with a greater load the friction is lowered to a point but it is always lower than boundary.
So with the use of smaller mains the load is proportionally increased, this helps the bottom number in the division by making it a larger number, the top number is made smaller by the fact as mentioned earlier the K factor. So it is win win in regards to friction. While friction is reduced due to lower viscosity oils, I wouldn't go there, some Nascar Teams still use 20W-50 and that is where I will stay unless there is a need for a 60 weight oil which some race cars use.
While doing my research for this topic I dug up this info from the SAE.
http://www.sae.org/events/pfs/presen...2005spikes.pdf
On page 46 there is the conclusion to a wear study that was conducted and the basis of the study was ZDDP and its effects. Now this might explain something that is important to all of us.
That is why some oils have caused high wear or maybe put another way allowed high wear. So oils that are not high in ZDDP may be doing more damage than oils with none! This may explain problems seen with Mobil 1. Various grades of Mobil 1 have different formulations.Another Rennlister JET951 may like to expand on this is his area given that he rebuilds these engines. Also if I understood it correctly there is increased friction when there is mixed lubrication when ZDDP is used. Maybe this is a by product of the mechanism of action? That is the protection offered slightly increases the friction.
There is some other issues that may be of interest, I will try to explain the terminology as best I can so that it makes sense, I have condensed the article so that if you have a question please ask it.
Back to the types of lubrication, boundary lube. is when there is a few molecules of oil between the sliding surfaces and the peaks of each surface touch each other. This is the highest friction and occurs on cold start up, a hydrodynamic wedge forms as the journal rotates and the oil is trapped. There is little pressures on the edges as the pressure escapes and peak pressure is in the centre of the bearing.
This is why grooved bearings cannot carry anywhere near the same load, (If a pic is desired i can draw it but the article and photos are copyright protected) if the bearing was wide enough pressure would peak and be level in the centre. I think that Porsche when they made this change, were just worried about the damage to the rod bearings that was happening in the marketplace and tried this as a fix not because it was better.
The film thickness may only be around 0.0001" but the pressure may be as high as 6,000 psi. Hydrodynamic pressure has nothing to do with engine oil pressure, the only relationship will be is there enough oil to cool the bearings and keep the hydrodynamic wedge going. Also the opening out of the oil galleries on the rod journals is bad for the same reasons. The opening needs to be kept small with only a small radius to relieve any stress.
The third mode is mixed, that is part hydrodynamic and part boundary. It is the transition between the two types of lubrication. There is a another type of lube that is not applicable to fluid film bearings and that is squeeze film. It is the type of lubrication that is seen in wrist or piston pins.
A bit of terminology, bearing eccentricity, I normally associated this with rod bearings, however it is also associated with the lubrication modes. Bearing eccentricity is the journal displacement from the centreline of the housing. That is off to one side, the journal does start to climb the wall of the journal as the journal or shaft starts turning.
An example may be, the mains or rods may have a 0.003" clearance. Or a radial clearance of 0.0015" and is operating with a oil film thickness of 0.0001". The sum would be (0.0015 - 0.0001)/0.0015= 0.9333" The actual shaft/journal diameter was not supplied in the article so that was not that helpful.
Looking at the Stribeck graph it shows that the friction starts off very high and as the journal starts to turn the hydrodynamic pressure starts to build and take over from the boundary lube. If rpm stays fixed and either viscosity decreases or unit load increases it will eventually reach its low point of friction of a BOC of 35. That value put into perspective is half the friction of a deep groove ball bearing.
If the loading continues to go up and or the viscosity decreases the BOC will move into the mixed lube mode where there is minor metal to metal contact. If this happens you have too low a viscosity oil or your bearings are too narrow.
I believe one of the reasons the crank that I have that looks like a mirror is polished in that way, is that they are are trying to keep those peaks and valleys to an absolute minimum to reduce this mixed lubrication.
From the low point of BOC 35 it only goes one way, if higher revs or higher viscosity or lower unit load, the friction rises exponentially or to approx ten times the low point. This is why much attention is paid to getting this right. Designers need to maintain the 35 to 50 BOC range.
So to sum up, when you change the mains and or rod journals to a smaller diameter, the unit load increases and the bearing speed decreases, two good things for lowering mechanical losses. I put this forward as some research to be discussed to hopefully move our engines forward. If anybody wants to contact me off list about a potential future crank order they can at ggray1964 at yahoo dot com I believe it needs more research and that will take time but I am in no hurry at present.
Otherwise happy to kick it around here for a while, there is a few more things to add but the wife wants me off the computer as we are on holidays
Cheers Greg
10-27-2009, 09:29 AM
#2
Supercharged
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Wow! What a kick *** post! And a super find on the ZDDP.
Most of your post was WAY over my head, but that's nothing new, I know. Let me throw out an un-educated wrench into your mix to see what you think.
It was postulated by someone I know, that another possible issue with 928 engine design is rod clearance. It's my understanding that the stock 928 rod clearances are about 5 or 6 thousandths (in). His theory is that under race/aggresive applications this may not be sufficient enough clearance to allow the oil to escape to keep the bearing surfaces cool. Further to his argument, he cited that many of the stroker cranks/rod combinations allow for rod clearances of upto 10-12 thousandths (in) and they don't seem to have the bearing problems that seem to follow the stock crank.
OK, now before my brain is about to explode... Does any of that make sense? It did to me, but I must admit I was drinking at the time.
Most of your post was WAY over my head, but that's nothing new, I know. Let me throw out an un-educated wrench into your mix to see what you think.
It was postulated by someone I know, that another possible issue with 928 engine design is rod clearance. It's my understanding that the stock 928 rod clearances are about 5 or 6 thousandths (in). His theory is that under race/aggresive applications this may not be sufficient enough clearance to allow the oil to escape to keep the bearing surfaces cool. Further to his argument, he cited that many of the stroker cranks/rod combinations allow for rod clearances of upto 10-12 thousandths (in) and they don't seem to have the bearing problems that seem to follow the stock crank.
OK, now before my brain is about to explode... Does any of that make sense? It did to me, but I must admit I was drinking at the time.
Last edited by AO; 10-27-2009 at 11:00 AM.
10-27-2009, 10:11 AM
#3
Administrator - "Tyson"
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Interesting in that no ZDDP is better than low levels of ZDDP while high levels are ideal.
50ppm and 100ppm oil showed more wear than oil with zero ZDDP. 50ppm was actually "better" than 100ppm
The three ranges that showed better wear than the no ZDDP oil were 200, 300, and 500 parts per million. This almost makes that entire study irrelevant to us since even the low ZDDP GF-4 oils have 800ppm of ZDDP.
Interesting in that no ZDDP is better than low levels of ZDDP while high levels are ideal.
50ppm and 100ppm oil showed more wear than oil with zero ZDDP. 50ppm was actually "better" than 100ppm
The three ranges that showed better wear than the no ZDDP oil were 200, 300, and 500 parts per million. This almost makes that entire study irrelevant to us since even the low ZDDP GF-4 oils have 800ppm of ZDDP.
10-27-2009, 10:35 AM
#4
Drifting
Greg, excellent post as usual! 
After reading that, I am now very happy in my decision to retain the stock redline in my racecar (..less complexity), but I'm sure you're thinking/smirking: 'what fun is that?!'
Keep up the good work, and please continue to post your findings.
After reading that, I am now very happy in my decision to retain the stock redline in my racecar (..less complexity), but I'm sure you're thinking/smirking: 'what fun is that?!'
Keep up the good work, and please continue to post your findings.
10-27-2009, 11:13 AM
#5
Team Owner
Greg, thanks for sharing this info.
I was wondering what holds the bushed insert in the block??
What holds it from front to back forces and from turning in the block?( with the 928 clutch it will be pulled rearwards)
Is it pinned somehow?
I was wondering what holds the bushed insert in the block??
What holds it from front to back forces and from turning in the block?( with the 928 clutch it will be pulled rearwards)
Is it pinned somehow?
10-27-2009, 11:25 AM
#6
Nordschleife Master
To the extent that you are looking to reduce friction and reduce the power loss to the oil pump, smaller main journals indeed make sense. The material selection may also help with clearances.
I am not arguing that this will be beneficial if you get it to work. However, I am questioning at which point of the rev range is this necessary and/or benefits exceed the costs.
Ford 351W engine has either 3" or 2.75" main journals. In particular, Ford Racing rates the 351 Sportsman block that has 3" main journals to 7000 rpm. Ford Racing rates their other blocks that have 2.75" journals to 8700 rpm.
Now, the 928 engine has 2.756" (69.990mm) main journals. It seems to me, and perhaps this is naive, that with Ford's criteria and standards those should also live to 8700 rpm.
By 8700 rpm, the rest of my 928 engine has already checked itself into the scrap metal bin. Not yours necessarily, since you are changing everything else. But for someone who's not completely redesigning the entire engine, are the friction benefits from the lower bearing speed and the benefits from lower oil pumping losses worth the cost? How many dollars per hp at a given rpm?
I am not arguing that this will be beneficial if you get it to work. However, I am questioning at which point of the rev range is this necessary and/or benefits exceed the costs.
Ford 351W engine has either 3" or 2.75" main journals. In particular, Ford Racing rates the 351 Sportsman block that has 3" main journals to 7000 rpm. Ford Racing rates their other blocks that have 2.75" journals to 8700 rpm.
Now, the 928 engine has 2.756" (69.990mm) main journals. It seems to me, and perhaps this is naive, that with Ford's criteria and standards those should also live to 8700 rpm.
By 8700 rpm, the rest of my 928 engine has already checked itself into the scrap metal bin. Not yours necessarily, since you are changing everything else. But for someone who's not completely redesigning the entire engine, are the friction benefits from the lower bearing speed and the benefits from lower oil pumping losses worth the cost? How many dollars per hp at a given rpm?
10-27-2009, 11:39 AM
#7
Supercharged
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To the extent that you are looking to reduce friction and reduce the power loss to the oil pump, smaller main journals indeed make sense. The material selection may also help with clearances.
I am not arguing that this will be beneficial if you get it to work. However, I am questioning at which point of the rev range is this necessary and/or benefits exceed the costs.
Ford 351W engine has either 3" or 2.75" main journals. In particular, Ford Racing rates the 351 Sportsman block that has 3" main journals to 7000 rpm. Ford Racing rates their other blocks that have 2.75" journals to 8700 rpm.
Now, the 928 engine has 2.756" (69.990mm) main journals. It seems to me, and perhaps this is naive, that with Ford's criteria and standards those should also live to 8700 rpm.
By 8700 rpm, the rest of my 928 engine has already checked itself into the scrap metal bin. Not yours necessarily, since you are changing everything else. But for someone who's not completely redesigning the entire engine, are the friction benefits from the lower bearing speed and the benefits from lower oil pumping losses worth the cost? How many dollars per hp at a given rpm?
I am not arguing that this will be beneficial if you get it to work. However, I am questioning at which point of the rev range is this necessary and/or benefits exceed the costs.
Ford 351W engine has either 3" or 2.75" main journals. In particular, Ford Racing rates the 351 Sportsman block that has 3" main journals to 7000 rpm. Ford Racing rates their other blocks that have 2.75" journals to 8700 rpm.
Now, the 928 engine has 2.756" (69.990mm) main journals. It seems to me, and perhaps this is naive, that with Ford's criteria and standards those should also live to 8700 rpm.
By 8700 rpm, the rest of my 928 engine has already checked itself into the scrap metal bin. Not yours necessarily, since you are changing everything else. But for someone who's not completely redesigning the entire engine, are the friction benefits from the lower bearing speed and the benefits from lower oil pumping losses worth the cost? How many dollars per hp at a given rpm?
Obviously it's not just one variable. I don't know **** about this stuff, but I'm trying to learn.
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10-27-2009, 12:52 PM
#8
Race Car
Another article pointing to the fact that lower oil viscosity is directly proportional to higher metallic wear. Don't buy into the hype that the 5W40 oils are better for a 928.
Dan
'91 928GT S/C
475hp/460lb.ft
Dan
'91 928GT S/C
475hp/460lb.ft
10-27-2009, 01:03 PM
#9
Nordschleife Master
random rpm musings
Doesn't stroke come into play? I always thought the longer the stroke, the lower the redline. I believe the stroke on that Ford engine is ~88mm where as on a STOCK S4 it's 79mm. Not sure what kind of stroke Greg is planning on his motor, but in theory, we should be able to rev the crap out of our stock motors as long as we can oil it properly. Obviously it's not just one variable. I don't know **** about this stuff, but I'm trying to learn.
What Greg is working on here is two things. First, lower the frictions at the main bearings. Because diameter is smaller, bearing surface speed is lower, and friction is also lower. Second, if the oil is aerated or cavitates for some other reason, oil needs to be first pushed to the center of the main bearing by the oil pump. This is against the centrifugal force, which in term depends on the main bearing radius. Smaller the radius, lower the centrifugal force, and lower the required oil pressure. Thus, less parasitic losses.
The stroke is also important for the safe RPM limit. First, there's the max piston speed, which goes up with stroke. With modern pistons (less than 40 years old), that's not a binding constraint. Second, there are piston accelerations, which also increase with stroke. Piston accelerations are directly relevant because ring flutter. Determining the limits would require either experimenting or simulation software such as Ricardo's RingPak. Third, piston accelerations are indirectly relevant because of the associated forces stress the crank, conrods, piston wrist pins, etc. One can increase the strength or reduce weight to increase the red line, I think the redline new / redline old is proportional to the sqrt(weight old / weight new). Note that above is about safe rpm limit, not about low friction.
10-27-2009, 01:47 PM
#10
Drifting
Piston stroke and valve float are the two things that really constrain engine speed. Engine controller processor power can also come into play on new stuff.
High rpm engines are very cool and sound fantastic. They are however much more expensive to build than forced induction engines making similar or more power.
High rpm engines are very cool and sound fantastic. They are however much more expensive to build than forced induction engines making similar or more power.
10-27-2009, 02:11 PM
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Ah, I was waiting for a forced induction comment. I love you guys.
Seriously, piston acceleration comes in to play by the rod/stroke ratio as well as the stroke itself for our speculations here. I have thought for years the Infinity v8's are some of the best v8 engines ever built. I find it interesting they redline around 7000 rpm and have only six counterweights. I still believe eight are better. There are other considerable differences (factory forged rods and crank, lighter pistons, hey it's newer). Here's a little technical info for any who care http://www.nicoclub.com/articles/VH45-information.pdf. I plan to pull the bottom end apart on my vh45 and make some comparisons to my 928 block after I'm done doing flow studies on the girdle. I plan to make a new post about that soon BTW.
Seriously, piston acceleration comes in to play by the rod/stroke ratio as well as the stroke itself for our speculations here. I have thought for years the Infinity v8's are some of the best v8 engines ever built. I find it interesting they redline around 7000 rpm and have only six counterweights. I still believe eight are better. There are other considerable differences (factory forged rods and crank, lighter pistons, hey it's newer). Here's a little technical info for any who care http://www.nicoclub.com/articles/VH45-information.pdf. I plan to pull the bottom end apart on my vh45 and make some comparisons to my 928 block after I'm done doing flow studies on the girdle. I plan to make a new post about that soon BTW.
10-27-2009, 02:24 PM
#12
Nordschleife Master
I considered turboing a vk45de before starting this 928 project. There's almost no performance stuff available for vk45de. Mostly it's because there's not a whole lot to improve, starting from titanium valves stock. But a turbo kit and ECU reprogam for my Infiniti M45 Sport would be nice. I did ask a quote from a Japanese firm for buliding a twin turbo vk45de. They said over $50k, likely $100k. I didn't send them the $20k deposit... ;-) Vh would have been more economical, for sure. The Kuhn TT 928 is going to be more fun and is going to cost a lot less.
Let me (us) know about your girdle experiment results!
Let me (us) know about your girdle experiment results!
Ah, I was waiting for a forced induction comment. I love you guys.
Seriously, piston acceleration comes in to play by the rod/stroke ratio as well as the stroke itself for our speculations here. I have thought for years the Infinity v8's are some of the best v8 engines ever built. I find it interesting they redline around 7000 rpm and have only six counterweights. I still believe eight are better. There are other considerable differences (factory forged rods and crank, lighter pistons, hey it's newer). Here's a little technical info for any who care http://www.nicoclub.com/articles/VH45-information.pdf. I plan to pull the bottom end apart on my vh45 and make some comparisons to my 928 block after I'm done doing flow studies on the girdle. I plan to make a new post about that soon BTW.
Seriously, piston acceleration comes in to play by the rod/stroke ratio as well as the stroke itself for our speculations here. I have thought for years the Infinity v8's are some of the best v8 engines ever built. I find it interesting they redline around 7000 rpm and have only six counterweights. I still believe eight are better. There are other considerable differences (factory forged rods and crank, lighter pistons, hey it's newer). Here's a little technical info for any who care http://www.nicoclub.com/articles/VH45-information.pdf. I plan to pull the bottom end apart on my vh45 and make some comparisons to my 928 block after I'm done doing flow studies on the girdle. I plan to make a new post about that soon BTW.
10-27-2009, 02:26 PM
#13
Nordschleife Master
Yes, but how are you going to make the 928 5-speed manual last? I think you need lower torque and higher revs, otherwise the transmission is going to give up the ghost.
10-27-2009, 02:26 PM
#14
Supercharged
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We're in the same camp, I don't know **** either. That said, I'll display my ignorance and speculate a bit.
What Greg is working on here is two things. First, lower the frictions at the main bearings. Because diameter is smaller, bearing surface speed is lower, and friction is also lower. Second, if the oil is aerated or cavitates for some other reason, oil needs to be first pushed to the center of the main bearing by the oil pump. This is against the centrifugal force, which in term depends on the main bearing radius. Smaller the radius, lower the centrifugal force, and lower the required oil pressure. Thus, less parasitic losses.
The stroke is also important for the safe RPM limit. First, there's the max piston speed, which goes up with stroke. With modern pistons (less than 40 years old), that's not a binding constraint. Second, there are piston accelerations, which also increase with stroke. Piston accelerations are directly relevant because ring flutter. Determining the limits would require either experimenting or simulation software such as Ricardo's RingPak. Third, piston accelerations are indirectly relevant because of the associated forces stress the crank, conrods, piston wrist pins, etc. One can increase the strength or reduce weight to increase the red line, I think the redline new / redline old is proportional to the sqrt(weight old / weight new). Note that above is about safe rpm limit, not about low friction.
What Greg is working on here is two things. First, lower the frictions at the main bearings. Because diameter is smaller, bearing surface speed is lower, and friction is also lower. Second, if the oil is aerated or cavitates for some other reason, oil needs to be first pushed to the center of the main bearing by the oil pump. This is against the centrifugal force, which in term depends on the main bearing radius. Smaller the radius, lower the centrifugal force, and lower the required oil pressure. Thus, less parasitic losses.
The stroke is also important for the safe RPM limit. First, there's the max piston speed, which goes up with stroke. With modern pistons (less than 40 years old), that's not a binding constraint. Second, there are piston accelerations, which also increase with stroke. Piston accelerations are directly relevant because ring flutter. Determining the limits would require either experimenting or simulation software such as Ricardo's RingPak. Third, piston accelerations are indirectly relevant because of the associated forces stress the crank, conrods, piston wrist pins, etc. One can increase the strength or reduce weight to increase the red line, I think the redline new / redline old is proportional to the sqrt(weight old / weight new). Note that above is about safe rpm limit, not about low friction.
Um.... you obviously know way more than I do on this ****. I can't even remember the last time I had to take the sqrt of something. Owww! My head!... LOL! Piston stroke and valve float are the two things that really constrain engine speed. Engine controller processor power can also come into play on new stuff.
High rpm engines are very cool and sound fantastic. They are however much more expensive to build than forced induction engines making similar or more power.
High rpm engines are very cool and sound fantastic. They are however much more expensive to build than forced induction engines making similar or more power.
10-27-2009, 02:29 PM
#15
Race Car
Ah, I was waiting for a forced induction comment. I love you guys.
Seriously, piston acceleration comes in to play by the rod/stroke ratio as well as the stroke itself for our speculations here. I have thought for years the Infinity v8's are some of the best v8 engines ever built. I find it interesting they redline around 7000 rpm and have only six counterweights. I still believe eight are better. There are other considerable differences (factory forged rods and crank, lighter pistons, hey it's newer). Here's a little technical info for any who care http://www.nicoclub.com/articles/VH45-information.pdf. I plan to pull the bottom end apart on my vh45 and make some comparisons to my 928 block after I'm done doing flow studies on the girdle. I plan to make a new post about that soon BTW.
Seriously, piston acceleration comes in to play by the rod/stroke ratio as well as the stroke itself for our speculations here. I have thought for years the Infinity v8's are some of the best v8 engines ever built. I find it interesting they redline around 7000 rpm and have only six counterweights. I still believe eight are better. There are other considerable differences (factory forged rods and crank, lighter pistons, hey it's newer). Here's a little technical info for any who care http://www.nicoclub.com/articles/VH45-information.pdf. I plan to pull the bottom end apart on my vh45 and make some comparisons to my 928 block after I'm done doing flow studies on the girdle. I plan to make a new post about that soon BTW.
Dan
'91 928GT S/C
475hp/460lb.ft
Last edited by dprantl; 10-27-2009 at 02:48 PM.
