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Corvette 6 spd in place of 928 AT?

 
Old 10-06-2005, 12:56 PM
  #46  
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What some folks here are not seeing is that 450 '#s of torque are breaking transmissions ON THE TRACK! They will hold up to considerably more in "normal" street driving where you are at full throttle a very low percentage of the time. 450'# of torque is not the magical number that explodes transmissions, it's the level where they cannot handle competition extremes.
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Old 10-06-2005, 01:24 PM
  #47  
Jim bailey - 928 International
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Dave makes an excellent point . If you tried to drive like Mark Anderson , Joe Fan , Don Hanson, ETC. race, but on the street you would be dead or in jail long before you broke a transmission. Take it to the drag strip and sure you can break things because EVERYTHING breaks on drag race cars...jump on the Vette chat rooms and they complain about breaking their gearboxs far too often when drag racing.
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Old 10-06-2005, 02:18 PM
  #48  
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Originally Posted by TAREK
ok...we know some 928 racers have more than 450ft/lb at the rear wheels. Big Bird may have more than 550ft/lb...Lag has about that much and Tim Murphy possibly more than 600ft/lb...so we know the 5 spd can handle about that much. The 928 racer you mentioned may be slightly off ?

I guess there are no real world failure tests for the AT

No second guessing the 950hp guys...so the failure point is somewhere above 600 but below 950 for the 5spd?

Seems that given the availability and cost of parts, the only tranny custom fitting that is worth doing are the T-56 or Merecedes AT like someone mentioned in this thread
I guess it boils down to abuse too. I dont think 450 ft/lb is a magic number, but I am sure if it is driven at the limit for long enough it would fail. On the street with an occasional blast to 550 ft/lb, it might last for a while. It would be interesting to find out from Porsche what it was actually designed for.

On autos, I have heard both sides, a little less and a little more and nobody really knows.

I talked to another turbo builder and he did say, that shop tended to inflate their numbers. Just guessing, I would bet they were running around 20 # of boost and it was on a bored out S4 motor. That should put you at +- 800 hp and 700 ft/lb of torque. Still a lot, but consider they broke everything in the drivetrain multiple times and that was while they were still setting it up, dyno testing etc, and no real continuous driving.

At the end of my " I want to build a 928 turbo" conversation with him, he said "you should be driving a 930"

I think its like Jim said above. If you take it easy you might last a while at 600 ft/lb but drag racing with sticky tires, you might blow at 400 ft/lb.
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Old 10-06-2005, 02:27 PM
  #49  
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Originally Posted by tammons
......... t the end of my " I want to build a 928 turbo" conversation with him, he said "you should be driving a 930" ...
Looking at stock 930 numbers and having chased down a '76 myself, I'd say for the price of a forced-induction 928 you could not get a comparably-built 930.
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Old 10-06-2005, 03:54 PM
  #50  
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Tammons part of why the actual drag strip time slips we see for basically stock 928s are often better than the official factory or old magazine article tests include the improvement in tires in general plus the preparation of the drag strip surface application of sticky stuff etc. I spoke with the contractor who poured the surface at Pomona which he said was less than 1 inch from being level from start to finish. The 928 with approx 50/50 weight distribution does better than many but NEVER approaches the favorable rear bias of a 930. My old 911 race car was about 70/30 and would nearly pull a wheelie ! which of course made it handle poorly on a road race course. But the increased traction at a drag strip also means increased loads on the driveline compared to the stop light Gran Prix. One factor which is THOUGHT to be involved in transmission failure is excessive heat in the transmission causing the case to expand and the gears to move away from each other.That theory is perhaps indirectly supported when you consider that Porsche added an oil pump and oil cooler oil spray to the GTS 5 speed transmission. The original design for the 5 speed anticipated engines from 4.5 liter to 5.5 liters and over the years there were increases in the size of some of the bearings.
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Old 10-06-2005, 04:02 PM
  #51  
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Originally Posted by Jim bailey - 928 International
Tammons part of why the actual drag strip time slips we see for basically stock 928s are often better than the official factory or old magazine article tests include the improvement in tires in general plus the preparation of the drag strip surface application of sticky stuff etc. I spoke with the contractor who poured the surface at Pomona which he said was less than 1 inch from being level from start to finish. The 928 with approx 50/50 weight distribution does better than many but NEVER approaches the favorable rear bias of a 930. My old 911 race car was about 70/30 and would nearly pull a wheelie ! which of course made it handle poorly on a road race course. But the increased traction at a drag strip also means increased loads on the driveline compared to the stop light Gran Prix. One factor which is THOUGHT to be involved in transmission failure is excessive heat in the transmission causing the case to expand and the gears to move away from each other.That theory is perhaps indirectly supported when you consider that Porsche added an oil pump and oil cooler oil spray to the GTS 5 speed transmission. The original design for the 5 speed anticipated engines from 4.5 liter to 5.5 liters and over the years there were increases in the size of some of the bearings.
Thanks Jim for the interesting info for sure. I always thought that Bello 911 was pretty cool. Nothing like a 911 doing a wheelie. Personally I have backed off the high performance 5 speed 928 stuff for now and am back to crusing around in a 83S dead simple totally stock automatic and loving it.

BTW, have you ever heard design #'s for the 928 5 speed box. I would assume it would be a certain level of HP/TQ plus a safety factor of some sort.
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Old 10-06-2005, 04:27 PM
  #52  
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Originally Posted by GUMBALL
If you are looking for a special purpose trans-axle, try browsing thru these links, SOMETHING will fit, hold the power, and have a selection of final drives and change ratios]
Richmond has a 6spd for a pretty reasonably price (<$3k):
http://www.sallee-chevrolet.com/Rich...Speed_ROD.html
It has a removable tailshaft and no bell housing so it looks like it could fit. Comes in a variety of gear ratios.
They also have their 5spds for less than ($2k) which have been around forever and are fairly bulletproof:
http://www.richmondgear.com/01fivespeed.html
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Old 10-06-2005, 05:11 PM
  #53  
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The problem with using the Richmond box (or other similar transmissions) is that they are not TRANS-AXLES........what are you planning to use for a diff assy..??
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Old 10-06-2005, 05:16 PM
  #54  
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Originally Posted by GUMBALL
The problem with using the Richmond box (or other similar transmissions) is that they are not TRANS-AXLES........what are you planning to use for a diff assy..??
The diff from an auto box would be certainly be one option.
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Old 10-06-2005, 05:24 PM
  #55  
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Originally Posted by sublimate
The diff from an auto box would be certainly be one option.
...and start off your project by fabricating bits to mate this transmission to that diff assy..?? think of the cost in that..?? and what size will the mated trans/diff assy be..??

That is why Hewland, Ricardo, X-Trac, Emco, etc, etc, do what they do - they build a PACKAGE, that is already engineered and tested...there are enough bits to fabricate as it is - mounts, driveshaft-to-trans adaptor, mating halfshafts to diff flanges, shift linkage, etc...
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Old 10-06-2005, 05:32 PM
  #56  
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While the 5 speed transmision and ring and pinion is all in a single case the automatic which started life as a Mercedes unit designed to be bolted to the engine has a seperate differential housing case which BOLTS to the tail of the Mercedes unit converting it into a transaxle. Even the pinion gear is bolted on ! The one real attempt to use an alternative manual transmission that I am aware of was adapting the case for an automatic to the rear of the transmission. In that case to preserve the PSD computer limited slip as it was a 1990 car as I recall
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Old 10-06-2005, 05:32 PM
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Originally Posted by GUMBALL
...and start off your project by fabricating bits to mate this transmission to that diff assy..?? think of the cost in that..??

That is why Hewland, Ricardo, X-Trac, Emco, etc, etc, do what they do - they build a PACKAGE......
Have you converted 28,000 BP to US $ in a while?
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Old 10-06-2005, 05:37 PM
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Originally Posted by sublimate
Have you converted 28,000 BP to US $ in a while?
...check Emco boxes.....
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Old 10-06-2005, 05:38 PM
  #59  
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When I Break something I will figure out what to replace.
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Old 10-06-2005, 05:38 PM
  #60  
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Originally Posted by GUMBALL
...and start off your project by fabricating bits to mate this transmission to that diff assy..?? think of the cost in that..?? and what size will the mated trans/diff assy be..??
That is one of the easier parts of the conversion. Engine/tranny/t-case adapters are built all the time for hotrods and offroad vehicles.
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