"Uber Performance" 928 Crankshafts Are Here!
04-19-2012, 03:31 PM
#31
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Brad, the pictured crank has a GTS-spec stroke- 85.9 mm. That's 7mm greater than your 78.9 mm-stroke 5L crank. So with stock rods and pistons, the piston will poke 3.5 mm out of the bore at TDC. Compression will be a little high....
IIRC I think there's also a 'screamer' 78.9 mm ('stock' 5L) stroke crank in the works.
IIRC I think there's also a 'screamer' 78.9 mm ('stock' 5L) stroke crank in the works.
04-19-2012, 04:27 PM
#32
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All of my new cranks are made with a rod journal size that allow us/the customer to buy a huge variety of rod bearings....which allows us/the customer to pick a rod bearing that is appropriate for the intended use. Softer low eccentricity bearings are available, for street use, and harder high eccentricity bearings are available for racing use...plus everything that you could imagine, between these two extremes.
To use any of these cranks, there isn't an "existing" connecting rod that will fit. All the rods need to be custom to fit with these strokes and with the proper big end sizes to fit on the crankshaft.
04-19-2012, 06:30 PM
#34
11-06-2015, 01:14 AM
#36
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Cool, getting close! Gotta stop by and check it out.
11-06-2015, 08:00 PM
#39
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I get that you can use this with stock GTS pistons and custom rods (or lightweight GB pistons.. still don't know how the crank can be balanced for both unless GB pistons are the same as GTS pistons) and , do those pistons have the coatings for the alusil block? I always thought that was a risk, so 968 pistons were used in strokers or the block was nicasiled.
why not just use a higher stroke and get more displacement and use the GTS pistons? i think that was the cheap way in the day with devek and their 6 liter strokers..... use stock block and special pistons with the coating like Gregory's stroker.. (still running today after 100k+ miles on the engine)
or is this just for the GTS screamer engine equivalent? after all, we are still only talking RPM of 6800rpm max or are we?
just curious of the purpose of this crank
11-06-2015, 08:10 PM
#40
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After noticing this thread and having interest, I just searched Greg's website.
It says:
ENGINE COMPONENTS:
· CRANKSHAFTS:
Moldex Cranks
Precision Motorwerks Crankshafts - 78.9, 85.9, and 95.25 mm stroke
It says:
ENGINE COMPONENTS:
· CRANKSHAFTS:
Moldex Cranks
Precision Motorwerks Crankshafts - 78.9, 85.9, and 95.25 mm stroke
11-07-2015, 02:14 PM
#42
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The history of larger displacement 928 engines, by prior builders, is littered with way more failures than successes. For every engine that actually worked, there were probably ten engines that either never ran or ran for very short periods of time.
While this "disaster" with other engine builders continues even today, I took the design and building of these larger engines to another level, by throwing away any of the original thinking and properly designing pieces that worked together properly. Once basic designs were perfected and the resulting engines were virtually bulletproof, it became possible to think about other options for engine designs. (Besides the fact that I get bored really quickly.)
For vehicles with automatic transmissions, the 6.5 liter engine is a perfect engine design. The huge amounts of torque are gobbled up by the torque convertor and transfered into fantastic rear wheel power, with relatively minor modifications to the transmission and drivetrain.
This combination is so perfect that it is difficult to imagine anything much better, in the automatic transmission equipped vehicles. These engines literally transform a 928 into a much more "current" motor vehicle, able to "compete" with almost any of the newer super cars.
The 6.5 liter combination of bore and stroke worked fine for the 5 speed versions of the 928 initially, however as engine development proceeded, it became evident (after my prototype intake system was tested) that any further development of low and middle range torque would be not only futile, but possibly dangerous. Rob Edward's GTS spun his huge rear tires virtually anytime the throttle was applied, which was quite fun, but also made directional stability quite tenuous.
I also became "re-interested" in the lighter "earlier" two valve vehicles and thought that a slightly higher rpm engine, with reduced torque, and quicker engine rpm change (faster reving) would be a natural for these vehicles.
Consequently, I started thinking about trading some of that low and midrange torque for higher rpm horsepower.
Since the rod angles, rod length, piston speed, component weight, exhaust pipe diameter (and resulting noise from larger pipes and mufflers) was a major factor in increasing the rpm range of the 95.25 x 104mm engines, different designs of engine pieces became intriguing to me. My intake system project was sidelined while these different engine designs were carefully considered.
The crankshafts you are seeing here are various versions from this designing. Shorter strokes allow smaller rod journals while retaining crankshaft stiffness and allowing lighter weight.
The pieces not shown, for these engine designs, are also different. Longer rods and different piston designs are obviously possible.
At the very least, these will be really interesting engines.
While this "disaster" with other engine builders continues even today, I took the design and building of these larger engines to another level, by throwing away any of the original thinking and properly designing pieces that worked together properly. Once basic designs were perfected and the resulting engines were virtually bulletproof, it became possible to think about other options for engine designs. (Besides the fact that I get bored really quickly.)
For vehicles with automatic transmissions, the 6.5 liter engine is a perfect engine design. The huge amounts of torque are gobbled up by the torque convertor and transfered into fantastic rear wheel power, with relatively minor modifications to the transmission and drivetrain.
This combination is so perfect that it is difficult to imagine anything much better, in the automatic transmission equipped vehicles. These engines literally transform a 928 into a much more "current" motor vehicle, able to "compete" with almost any of the newer super cars.
The 6.5 liter combination of bore and stroke worked fine for the 5 speed versions of the 928 initially, however as engine development proceeded, it became evident (after my prototype intake system was tested) that any further development of low and middle range torque would be not only futile, but possibly dangerous. Rob Edward's GTS spun his huge rear tires virtually anytime the throttle was applied, which was quite fun, but also made directional stability quite tenuous.
I also became "re-interested" in the lighter "earlier" two valve vehicles and thought that a slightly higher rpm engine, with reduced torque, and quicker engine rpm change (faster reving) would be a natural for these vehicles.
Consequently, I started thinking about trading some of that low and midrange torque for higher rpm horsepower.
Since the rod angles, rod length, piston speed, component weight, exhaust pipe diameter (and resulting noise from larger pipes and mufflers) was a major factor in increasing the rpm range of the 95.25 x 104mm engines, different designs of engine pieces became intriguing to me. My intake system project was sidelined while these different engine designs were carefully considered.
The crankshafts you are seeing here are various versions from this designing. Shorter strokes allow smaller rod journals while retaining crankshaft stiffness and allowing lighter weight.
The pieces not shown, for these engine designs, are also different. Longer rods and different piston designs are obviously possible.
At the very least, these will be really interesting engines.
Last edited by GregBBRD; 11-07-2015 at 02:54 PM.
11-07-2015, 09:54 PM
#45
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Some think that the port size is too large for the 5.0 engine and the very short rod is beneficial because of this, however I do not see this as an issue.....especially since these engines will be bigger than a 5.0.
Anything around 1.75 rod to stroke ratio is considered to be fairly optimal....and these engines will certainly fit into that category.