Crank, bottom end design, friction and oiling
10-27-2009, 02:34 PM
#16
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Even the most advanced ECU available is slow by normal computer standards.
10-27-2009, 02:50 PM
#17
Drifting
I wasn't specifically commenting on 928s. Just engine design in general. With respect to 928s...I suppose the ultimate solution would be to cut up the tunnel of the car and install a modified C5/C6 manual transmission.
10-27-2009, 04:56 PM
#21
Race Director
10-27-2009, 06:17 PM
#22
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10-27-2009, 07:52 PM
#23
Nordschleife Master
10-27-2009, 08:46 PM
#24
Race Director
Neither of my failed engines had any type of scraper system......the 1st was stock and the 2nd did have a couple mods, including the pan spacer and windage tray..but did NOT have a scraper.......and the failure appears to be component related (either crank or rod) failure.....not related to Doc Browns windage trays... The reason I DID NOT use a scraper system was three 928 engine builders whose opinion I trust BOTH said not to use one!
10-27-2009, 10:44 PM
#26
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By Andrew Olsen
Andrew thanks for your response, I take it you are talking about the side clearance on the rods and not the radial or bearing clearance, I also thought about this, out loud unfortunately. I haven't got time just now but it is just a mathematical question of calculating what the window size of the Porsche clearance is and what say the Chevy size is. I will try to do this later and get back to the board.
As to the question about the stroke and bore etc, well the parts and the plan I have are, piston 4.060" or 103.1 mm the rod length is 6.2" 157.5 mm and the stroke would be 3.543" or 90 mm. This gives a rod to stroke ratio 1.75 or the same as a GT3 engine. I would like the peak power to come in at upto 8,000 rpm and max rpm around 8200 rpm but it could be a touch higher but not much.
The reason when you look at the loadings, and speeds the average piston speed is just under 25 metres a second or about 24.6 metres a second and peak piston speed of 40 metres a second. This engine uses Nascar pistons rods and pins. The Nascar piston speeds/loadings are around 5% higher, so that is a little bit of conservatism and given it wont be subject long running like the Nascars do on ovals.
The piston pin material is very special stuff, Made by Del West it is C-350, extremely strong with a tensile strength of 350,000 psi.
http://www.allvac.com/allvac/pages/P.../VascoMaxC.pdf
The only issue with it is that the nickel can cause some galling, the pins are coated with a DLC from europe and I may have to have the rods brass bushed to combat this issue, the rods have the forced pin oiling which of course will assist in a long life. They even have a mirror polished internals. The diameter is 0.866" and it weighs 99 grams which is at the heavy end of Nascar stuff but it is designed to last not win a race.
What I would like to see is a group of like minded 928ers formed where certain interested parties take on various roles in building this all out 928 engine and the technology would then be shared and this co-operative development would hopefully take the 928 forward and further respect garnered for our cars.
An example would be someone would take on the manifold and another do the heads, other organize the cranks etc, however all designs before they were made would go before the committee to get agreement on the design.
I intend to flow the heads I have soon, I am looking for just a touch over 400 cfm of air a peak cam lift and the appropiate/better air velocity. There will be enough air I hope to support 800 hp. I have posted a Nascar dyno chart and that engine produced 821hp Nascar heads tend to be around 420 to 430 cfm at 0.900" lift
It is over 800 hp at 8,000 rpm, I have compared the flow charts of Nascar heads to the heads I have and what I hope to achieve with the flow rates. It should certainly will be comparable, the cam may be a problem but I'll leave that for the moment, I think anything over 700 hp is a winner regardless.
Greg
P.S have a look at the oil pressure, I am not suggesting such a low pressure but it gives you an idea of what is needed.
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.
As to the question about the stroke and bore etc, well the parts and the plan I have are, piston 4.060" or 103.1 mm the rod length is 6.2" 157.5 mm and the stroke would be 3.543" or 90 mm. This gives a rod to stroke ratio 1.75 or the same as a GT3 engine. I would like the peak power to come in at upto 8,000 rpm and max rpm around 8200 rpm but it could be a touch higher but not much.
The reason when you look at the loadings, and speeds the average piston speed is just under 25 metres a second or about 24.6 metres a second and peak piston speed of 40 metres a second. This engine uses Nascar pistons rods and pins. The Nascar piston speeds/loadings are around 5% higher, so that is a little bit of conservatism and given it wont be subject long running like the Nascars do on ovals.
The piston pin material is very special stuff, Made by Del West it is C-350, extremely strong with a tensile strength of 350,000 psi.
http://www.allvac.com/allvac/pages/P.../VascoMaxC.pdf
The only issue with it is that the nickel can cause some galling, the pins are coated with a DLC from europe and I may have to have the rods brass bushed to combat this issue, the rods have the forced pin oiling which of course will assist in a long life. They even have a mirror polished internals. The diameter is 0.866" and it weighs 99 grams which is at the heavy end of Nascar stuff but it is designed to last not win a race.
What I would like to see is a group of like minded 928ers formed where certain interested parties take on various roles in building this all out 928 engine and the technology would then be shared and this co-operative development would hopefully take the 928 forward and further respect garnered for our cars.
An example would be someone would take on the manifold and another do the heads, other organize the cranks etc, however all designs before they were made would go before the committee to get agreement on the design.
I intend to flow the heads I have soon, I am looking for just a touch over 400 cfm of air a peak cam lift and the appropiate/better air velocity. There will be enough air I hope to support 800 hp. I have posted a Nascar dyno chart and that engine produced 821hp Nascar heads tend to be around 420 to 430 cfm at 0.900" lift
It is over 800 hp at 8,000 rpm, I have compared the flow charts of Nascar heads to the heads I have and what I hope to achieve with the flow rates. It should certainly will be comparable, the cam may be a problem but I'll leave that for the moment, I think anything over 700 hp is a winner regardless.
Greg
P.S have a look at the oil pressure, I am not suggesting such a low pressure but it gives you an idea of what is needed.
10-27-2009, 11:20 PM
#27
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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 walls will impart a centripetal force.
</grammar police>
10-28-2009, 12:04 AM
#29
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By Swaybar
Thanks Swaybar, no not smirking at all, just want to hopefully supply info that is interesting and useful and hopefully this leads to existing engines lasting longer and new engines becoming more advanced. The thing about development, the more you learn the more you have to know and it often leads to the next question.
Also the way I am going about this is hopefully smart from the point of view that it is of minimal cost, that is copying it from the leaders in the industry which is most applicable to our engines. That is of course Nascar. These engineers are very smart. I have also gathered material from the racing GT3 engines which are very very close to this engine. Almost an identical bore, within 1 mm and the included angle of the valves in the head is the same. Just need to get the velocities and flow rates right to be in the 120+ hp per litre range. I am trying get my heads made and tested before christmas.
Also you would be surprised as long as your questions are sensible who will answer them. I feel very grateful to some of these people that have provided information and help. One thing is generally common is that they don't want to be named for fear of being overwhelmed with phone calls and emails.
In regard to engine management, if a few of these engines were built it would make sense to use the same system as then you would only have one lot of dyno time and the maps could be transferred and you may get a discount on the the system. To me that would be cost effective.
By Dprantl
Well there is nothing stopping us from doing this, I bought some motorbike COP stuff to investigate, I would not being running the distributors. (The COP stuff is to be used on the 2V stroker) Also with the big cam in this engine it will need to produce over 700 hp Variocam will be required. The engine simulations I ran showed increased vacuum at idle which was streetable. It would also use ITB as MIke and Louie have demonstrated so well it makes things much tamer.
Greg
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.
Also the way I am going about this is hopefully smart from the point of view that it is of minimal cost, that is copying it from the leaders in the industry which is most applicable to our engines. That is of course Nascar. These engineers are very smart. I have also gathered material from the racing GT3 engines which are very very close to this engine. Almost an identical bore, within 1 mm and the included angle of the valves in the head is the same. Just need to get the velocities and flow rates right to be in the 120+ hp per litre range. I am trying get my heads made and tested before christmas.
Also you would be surprised as long as your questions are sensible who will answer them. I feel very grateful to some of these people that have provided information and help. One thing is generally common is that they don't want to be named for fear of being overwhelmed with phone calls and emails.
In regard to engine management, if a few of these engines were built it would make sense to use the same system as then you would only have one lot of dyno time and the maps could be transferred and you may get a discount on the the system. To me that would be cost effective.
By Dprantl
Man, makes me wish I could drop that easily into a 928. No timing belt, Variocam built-in, sodium-cooled valves, distributorless COP ignition, fully sequential injection, etc. Probably too tall for a 928 engine compartment by the looks of the deep oil pan.
Dan
Dan
Greg
10-28-2009, 08:51 AM
#30
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A little bit more about the crank in the photos, that is a Nascar crank that was designed for the new Toyota Nascar engine. As many of you will know that when Toyota entered Cup competition because they couldn't adapt an engine from their road car range was able to use a clean sheet. As such they were able to take the best things from the three existing competitors.
They used the smallest journals possible, the mains are only 2" (smaller than our rod bearings) and the rod journals are 1.85". I must admit that I didn't ask the crank maker why the journal's webs were not edged in any way.
Also despite being fully countered weighted it is the lightest crank in the Nascar field and sometimes by around 8 pounds.
Some of this makes my head spin too, problem is my memory is bad and I can't remember exactly what i was told in regard to the mass movement of inertia or MMOI, normally the less weight that you have from the the furthest point of the crank centreline the better the spin up of the crank will be however it is tied in with crank stiffness. The bob weight is only 1500 grams and because of the use of the heavy metal the crank weighs around 35 pounds and if I recall correctly he said that it has an excellent MMOI.
The crank stiffness is important not just on a durability standpoint but going back to the earlier discussion about the hydrodynamic film, the deflection of the crank can ruin this of course and dramatically increase friction due to the increased leakage through greater radial clearances.
While generally a shorter crank will be a stiffer crank they are using increased thickness crank webs which means our cranks are great candidates for this and in fact the stroker cranks that have been made so far would employ this due to their use of the chevy width (axial width) pins which are narrower than the Porsche journals.
Also I noticed the Toyota crank has got a greater amount of material from the rod journals removed than my Moldex, they don't just drill through the journal but down towards the centre of the crank. Sort of like a filled in V.
So if there is any interest in this longer term project I will speak to the crank maker again and ask about some more of these details.They were generous with their information and time and I must admit when I heard how much Toyota spent with them, I thought he should have just hung up on me straight away.
From memory it was a batch order of ten cranks for $100,000 USD. "For that they got the best of everything" To get that kind of service with fine element analysis (FEA) for us at $3.5 K is pretty good, I am not making the use of small mains mandatory but the crank maker liked the idea when I told him of the power and rpms.
In discussing various crank designs there is still some cranks being used in Nascar that have 6 cwt, now I certainly can't talk about every Nascar engine builder, from what I have been able to discern is that some teams may run a 6 cwt crank on a road course and and run a 8 cwt on a oval, some for all I know will run a 6 cwt everywhere. It may however be a matter of cost or it could just be their opinion too.
When you look at the various makes of cranks, there is some big names like Meynard MCT who supply cranks to the Indy League, Chambon a French crank maker with a big reputation, Bryants have been there a long time and so have Winberg's. Given I have taken an interest in the Gibbs team as they seem to have a habit of winning;
it is interesting to see what they do compared to other teams.
I also bought three sets of headers from them (1 with minor damage) to make 2 sets net from them. This is where the crank came from and they certainly don't mind spending the bucks but their R&D seems superb and I am happy to get a free ride I have been told on another forum that their headers are impressive on the dyno and something I found interesting was they use the same headers on the open engines as they do on the plate motors, that said to me at the time these should work well on a street/track motor.
I rang the maker and they confirmed that the longevity will not be a problem, in fact they will probably out last the car. They are extremely light at just under 18 pounds for both sides and they are 36" If anybody wants some more details, happy to provide them, there is still some sets on Ebay but that wont last forever.
I will of course have to cut them up but there is lots of different curves to use amongst them. Welding them will not be easy as it is inconel 625 and requires practice like anything difficult but you will have a set of headers good for anything from 500 hp to 850 hp. Inconel 625 is often used for the turbine blades in jet engines, it is incredibly tough, just ask my hacksaw, the pipe is only 0.7 mm thick but it takes 2 blades to get through it
That pipe is only 1 3/4" too.
Greg
They used the smallest journals possible, the mains are only 2" (smaller than our rod bearings) and the rod journals are 1.85". I must admit that I didn't ask the crank maker why the journal's webs were not edged in any way.
Also despite being fully countered weighted it is the lightest crank in the Nascar field and sometimes by around 8 pounds.
Some of this makes my head spin too, problem is my memory is bad and I can't remember exactly what i was told in regard to the mass movement of inertia or MMOI, normally the less weight that you have from the the furthest point of the crank centreline the better the spin up of the crank will be however it is tied in with crank stiffness. The bob weight is only 1500 grams and because of the use of the heavy metal the crank weighs around 35 pounds and if I recall correctly he said that it has an excellent MMOI.
The crank stiffness is important not just on a durability standpoint but going back to the earlier discussion about the hydrodynamic film, the deflection of the crank can ruin this of course and dramatically increase friction due to the increased leakage through greater radial clearances.
While generally a shorter crank will be a stiffer crank they are using increased thickness crank webs which means our cranks are great candidates for this and in fact the stroker cranks that have been made so far would employ this due to their use of the chevy width (axial width) pins which are narrower than the Porsche journals.
Also I noticed the Toyota crank has got a greater amount of material from the rod journals removed than my Moldex, they don't just drill through the journal but down towards the centre of the crank. Sort of like a filled in V.
So if there is any interest in this longer term project I will speak to the crank maker again and ask about some more of these details.They were generous with their information and time and I must admit when I heard how much Toyota spent with them, I thought he should have just hung up on me straight away.
From memory it was a batch order of ten cranks for $100,000 USD. "For that they got the best of everything" To get that kind of service with fine element analysis (FEA) for us at $3.5 K is pretty good, I am not making the use of small mains mandatory but the crank maker liked the idea when I told him of the power and rpms.
In discussing various crank designs there is still some cranks being used in Nascar that have 6 cwt, now I certainly can't talk about every Nascar engine builder, from what I have been able to discern is that some teams may run a 6 cwt crank on a road course and and run a 8 cwt on a oval, some for all I know will run a 6 cwt everywhere. It may however be a matter of cost or it could just be their opinion too.
When you look at the various makes of cranks, there is some big names like Meynard MCT who supply cranks to the Indy League, Chambon a French crank maker with a big reputation, Bryants have been there a long time and so have Winberg's. Given I have taken an interest in the Gibbs team as they seem to have a habit of winning;
it is interesting to see what they do compared to other teams.I also bought three sets of headers from them (1 with minor damage) to make 2 sets net from them. This is where the crank came from and they certainly don't mind spending the bucks but their R&D seems superb and I am happy to get a free ride
I have been told on another forum that their headers are impressive on the dyno and something I found interesting was they use the same headers on the open engines as they do on the plate motors, that said to me at the time these should work well on a street/track motor.I rang the maker and they confirmed that the longevity will not be a problem, in fact they will probably out last the car. They are extremely light at just under 18 pounds for both sides and they are 36" If anybody wants some more details, happy to provide them, there is still some sets on Ebay but that wont last forever.
I will of course have to cut them up but there is lots of different curves to use amongst them. Welding them will not be easy as it is inconel 625 and requires practice like anything difficult but you will have a set of headers good for anything from 500 hp to 850 hp. Inconel 625 is often used for the turbine blades in jet engines, it is incredibly tough, just ask my hacksaw, the pipe is only 0.7 mm thick but it takes 2 blades to get through it
That pipe is only 1 3/4" too.Greg