New Crankshafts
02-15-2012, 06:11 PM
#46
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I shudder to think how much time and money you have tied up in this Greg.
When we both get time to build me a stroker I will be using your parts.
Any plans on parts for our 5 speeds?
The reason I ask is that at the power levels you are going to be able to make with all the neat parts is going to open up a new market for drive line parts.
Well done my friend.
When we both get time to build me a stroker I will be using your parts.
Any plans on parts for our 5 speeds?
The reason I ask is that at the power levels you are going to be able to make with all the neat parts is going to open up a new market for drive line parts.
Well done my friend.
I'm actually trying to move the power range "up", some, in the rpm range to take some of the transmission killing torque away.
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greg brown
714 879 9072
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Semi-retired, as of Feb 1, 2023.
The days of free technical advice are over.
Free consultations will no longer be available.
Will still be in the shop, isolated and exclusively working on project cars, developmental work and products, engines and transmissions.
Have fun with your 928's people!
greg brown
714 879 9072
GregBBRD@aol.com
Semi-retired, as of Feb 1, 2023.
The days of free technical advice are over.
Free consultations will no longer be available.
Will still be in the shop, isolated and exclusively working on project cars, developmental work and products, engines and transmissions.
Have fun with your 928's people!
02-15-2012, 06:12 PM
#47
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It's almost guaranteed that you're gonna catch SOMETHING dealing with lower priced hookers. You pays your money and you takes your chances
BTW Greg, Super nice job on the cranks and rods.
02-15-2012, 06:58 PM
#51
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It is sometimes virtually impossible to use pieces that were designed for street cars in race cars. This is one of those times.
Remember, the "1998" water cooled Cup Cars initally ran the "street" rod bearings that the 993 race engines ran. "Water" cooling allowed Porsche to add more ignition timing to these engines. They "spewed" connecting rods virtually as fast as Porsche could build the engines. A "quick" change, late in the 1998 season, to a different crank, different bearings, and different rods solved that issue. The latest Cup Car bearings have changed part numbers a few times, but the basic construction and hardness has not changed.
We can (and do) buy bearings , for my "new cranks and rods", that are very close to the bearings that Porsche runs in their Cup Car engines....perhaps even better.
If you just stop and think about the number of 928 engines that have failed when used for even "mild" track use, it is really sad.
Porsche had to know this, they certainly ran the engines on dynos. You'd certainly have to think that this is why they had such a "fit" when people wanted to race the 928s, early on.
Last edited by GregBBRD; 02-15-2012 at 09:46 PM.
02-15-2012, 09:20 PM
#52
Three Wheelin'
Since these crankshafts are designed for higher rpm use, there are actually 6 full counterweights and two "pro-stock" style counterweights. If you "dig" really deeply into the reasons for adding material to the "center" throws, the reason for adding this material has very little to do with "balance" or "smoothness".
Most "high end" crank builders will not make a crank, these days, with 8 "full" counterweights, unless the customer insists. Just a bunch of "extra worthless weight" slinging around, inside the engine. I talked to Whitey at Moldex, ten years ago, about adding two more counterweights to my 6 counterweight crank and he flat told me that this would be "stupid", considering the rpms these engines were turning. However, current camshaft, intake, and head design has "added" the ability to "twist" the 928 engine to higher rpms...which requires different thinking.
Anyway, 8 full counterweighted cranks are pretty "old" technology. Keep in mind that the GTS cranks were designed more than 20 years ago!
Stop and think about how far engine design has come, in the past 20+ years!
As I mentioned, these cranks are absolutely "new" in terms of design. Of course, the length and the basic rod and main bearing location doesn't change...but certainly, everything else has.
Most "high end" crank builders will not make a crank, these days, with 8 "full" counterweights, unless the customer insists. Just a bunch of "extra worthless weight" slinging around, inside the engine. I talked to Whitey at Moldex, ten years ago, about adding two more counterweights to my 6 counterweight crank and he flat told me that this would be "stupid", considering the rpms these engines were turning. However, current camshaft, intake, and head design has "added" the ability to "twist" the 928 engine to higher rpms...which requires different thinking.
Anyway, 8 full counterweighted cranks are pretty "old" technology. Keep in mind that the GTS cranks were designed more than 20 years ago!
Stop and think about how far engine design has come, in the past 20+ years!
As I mentioned, these cranks are absolutely "new" in terms of design. Of course, the length and the basic rod and main bearing location doesn't change...but certainly, everything else has.
I did realize that the 2 center counter weights were considerably smaller. Thanks for explaining it.
What I find very important in your new modern crank shafts with much better oiling system, is the ability to use much much higher quality rod bearings vs the much softer Porsche bearings. This will also, eliminate problems with sourcing the correct size Porsche rod bearing for a reliable engine.
Thanks for sharing, they look great.
02-15-2012, 10:52 PM
#53
Race Director
Notes to self.....Doc has FORGOT more than I can ever dream to know about 928 engines...but this quote makes me think:
"The "racer" that is building a "sometimes I'm going to go to a local PCA event" is going to spend $1500+ getting a stock crank "prepped" for use....and still have "agony" when he runs it.
You have to be realistic....if our engines had a "bullet proof" bottom end and people could go out and beat the crap out of them for hours and hours, they would be way more popular than they already are. However the "fragileness" of the 928 engine, combined with the history of idiots putting them together, has "scared" away a lot of potential customers.
I hope my "testing" on track of a stock 4.7 USA engine at sub 6000rpm with the 3/8 spacer and OB pan proves helpful....76 hours on track and counting...
"The "racer" that is building a "sometimes I'm going to go to a local PCA event" is going to spend $1500+ getting a stock crank "prepped" for use....and still have "agony" when he runs it.
You have to be realistic....if our engines had a "bullet proof" bottom end and people could go out and beat the crap out of them for hours and hours, they would be way more popular than they already are. However the "fragileness" of the 928 engine, combined with the history of idiots putting them together, has "scared" away a lot of potential customers.
I hope my "testing" on track of a stock 4.7 USA engine at sub 6000rpm with the 3/8 spacer and OB pan proves helpful....76 hours on track and counting...
02-15-2012, 11:02 PM
#54
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"new cranks and rods"
So these 'new' rods- different from my H-beam Carrillos?
02-16-2012, 01:41 AM
#56
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Yes. Actually, that was part of the plan.
Early stroker builders mistakenly used "Chevy" small block offset rods...in the 928 block. Completely different cylinder offsets between a Chevy and a 928.
All of my "new" cranks have a smaller rod journal than either a Porsche or a Small Block Chevy, which reduces the bearing speed. This will allow "higher" rpm usage with more reasonable bearing speeds.
Because of this, I created a "new rod" that only fits these crankshafts. Won't fit in a Chevy, so no danger of someone getting a crank and making the mistake of buying a Chevy rod and trying to make it fit.
These rods have the correct offset for a 928 engine, and fit on the smaller journals found on my new cranks. They are actually the same as my rods that Carrillo designed for use with my Moldex cranks but have a smaller "big end" size.
The rods are taper beam, with custom machining to reduce the weight in the beam, while still retaining all the strength. The "new" rods also feature a higher grade of bolt for higher rpm use. Still built by Carrillo, these rods are certainly some of the strongest and highest quality rods on the planet. Under 600 grams, if anyone cares about that detail.
I still have made and stock the rods needed for use with my older design crankshafts that have 2.100" journals (like your engine, Rob.) These rods fit almost all of the "stroker" cranks ever made (Moldex and Carrillo), so it is pretty easy for someone who has the incorrect offset Chevy rods to "swap" in the correct connecting rod.
Here's a couple of pictures:
Early stroker builders mistakenly used "Chevy" small block offset rods...in the 928 block. Completely different cylinder offsets between a Chevy and a 928.
All of my "new" cranks have a smaller rod journal than either a Porsche or a Small Block Chevy, which reduces the bearing speed. This will allow "higher" rpm usage with more reasonable bearing speeds.
Because of this, I created a "new rod" that only fits these crankshafts. Won't fit in a Chevy, so no danger of someone getting a crank and making the mistake of buying a Chevy rod and trying to make it fit.
These rods have the correct offset for a 928 engine, and fit on the smaller journals found on my new cranks. They are actually the same as my rods that Carrillo designed for use with my Moldex cranks but have a smaller "big end" size.
The rods are taper beam, with custom machining to reduce the weight in the beam, while still retaining all the strength. The "new" rods also feature a higher grade of bolt for higher rpm use. Still built by Carrillo, these rods are certainly some of the strongest and highest quality rods on the planet. Under 600 grams, if anyone cares about that detail.
I still have made and stock the rods needed for use with my older design crankshafts that have 2.100" journals (like your engine, Rob.) These rods fit almost all of the "stroker" cranks ever made (Moldex and Carrillo), so it is pretty easy for someone who has the incorrect offset Chevy rods to "swap" in the correct connecting rod.
Here's a couple of pictures:
Last edited by GregBBRD; 02-16-2012 at 01:56 AM.
02-16-2012, 02:13 AM
#57
Drifting
OMG Greg Those are feather weight, WOW awesome man.
A billet block you say, small journal crank, and these rods. OMG I see 9 -10,000 RPM.
This will cause more TT and drive line issues as It wont handle those Rrrrrz
Dont count me out but it will be a few years
A billet block you say, small journal crank, and these rods. OMG I see 9 -10,000 RPM.
This will cause more TT and drive line issues as It wont handle those Rrrrrz
Dont count me out but it will be a few years
02-16-2012, 02:31 AM
#58
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I still recall that comparison you showed me with the Carrillo rod and the (GTS?) factory rod clamped to the table (forget what it's called, the one with the Rockwell tester on it) , and the difference in beam stiffness- we should video that sometime, it's really striking. I'll wear the GoPro on my head.
02-16-2012, 03:45 AM
#59
Rennlist Member
Hi Greg – For your new 5.4L drop-in crank and rods, do you see any needed changes to valve train/lifters, etc? As a stock 93 GTS owner, replacing the rods has always been on the “to do” list; but now with the added benefit of your crank (and better bearings), I believe that would have to be added to the list too. Does this crank mean adding anything else to the short list? I'll never race this car, but I do want the confidence that it will perform as it should. Thanks / Bruce
02-16-2012, 04:28 AM
#60
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"Knife edge" is a term that appeared many years ago, in crank building. Basically, the leading edge of the counterweight was brought to a shape that resembled the shape of a huge knife. This was found to reduce windage, as the crank spins. This shape "gave way" to the more current completely rounded leading edge, which actually "creates" less windage than a sharper edge.
Some people still "cling" to the idea of using a "knife edge" on the trailing edge of a counterweight, but many think that a rounded edge works better, here also. The reality is that the oil is moving so fast on the counterweight, by the time it reaches the end, that it can't possibly conform to the shape of a 'knife edge" and probably simply flies straight off.
Some argue that an airplane wing is rounded on the front and is more "knife edge" shaped at the rear. The problem with this logic is that an airplace wing starts tapering to that "knife edge" almost immediately after the rounded edge cuts through the wind, not quickly terminated, like on a crank counterweight. The other problem with comparing an airplane wing to a crankshaft is that the crankshaft is turning through a virtually "solid" wall of oil at higher rpms.
Some people still "cling" to the idea of using a "knife edge" on the trailing edge of a counterweight, but many think that a rounded edge works better, here also. The reality is that the oil is moving so fast on the counterweight, by the time it reaches the end, that it can't possibly conform to the shape of a 'knife edge" and probably simply flies straight off.
Some argue that an airplane wing is rounded on the front and is more "knife edge" shaped at the rear. The problem with this logic is that an airplace wing starts tapering to that "knife edge" almost immediately after the rounded edge cuts through the wind, not quickly terminated, like on a crank counterweight. The other problem with comparing an airplane wing to a crankshaft is that the crankshaft is turning through a virtually "solid" wall of oil at higher rpms.
So guessing a bit, as my knowledge of aerodynamics and hydrodynamics is limited to assymetrical aerofoils in air (mostly sails but airplane wings are mostly the same) and symmetrical yacht foils in water at slow speeds (up to say 30mph.)
What could/may be of use would be to taper the trailing edge down to about 3-5mm thick and then machine the 3-5mm thick end face so it is not at 90 degrees to the direction of travel - change it to about 60-70 degrees , making
the travel path along the counterweight a tad shorter on one side than the other. This prevents equal and alternate vortex shedding that causes vibration, but could also result in the oil staying in suspension in the air for longer.