A transmission option for the high HP guys
03-12-2012, 03:51 AM
#1
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A transmission option for the high HP guys
After seeing Mike's thread about his broken trans,
https://rennlist.com/forums/928-foru...ing-video.html
I have to say that I been sitting on this idea for quite some time, given my current predicament with my health it is not likely to get done by me and after Mike's trans failure given all his mighty efforts with the 928 it has made me go public with this idea as it is right up his alley.
While some research would still need to be undertaken regarding some fitment issues, these issues I can't see putting a stop to this idea. So the concept of a Corvette ZR1 (TR6060) box is not entirely new, as Aspkiller certainly has proved. Cudos to him for his achievements too
There is a more than one way to skin a cat. (hope my mum never reads that)
The use of the ZR1 box is a good idea on many fronts, it is a cheap box to buy new or used. There is lots of good parts available to upgrade it and it is exceptionally strong, there is a choice of top gear ratios depending on the box sought, either performance or economy. There is also good parts with the associated driveline available, more on that later.
Nothing new there, how to go about implementing it? We are lucky that Porsche inadvertently gave us an option when they built the auto transmission. The fact that the rear housing for the differential unbolts like the Corvette is the real bonus. There is a sandwich plate that mates the ZF auto to the diff and this could be done with the Corvette manual and auto transmissions if one desired that.
The Corvette output shaft is quite beefy, in fact big enough to be cut down to the Porsche 928 output shaft size. The question I have there, is that I don't know enough about cutting that type of material. I don't believe it has been hardened in the area where, it would need shortening, two, the splines and threads would need cutting. Normally with the gearbox and driveshafts that I have seen the splines are the only area heat treated and hardened.
Cutting down and modifying the existing output shaft would have some advantages over making a part from scratch, as all the measurements internally in the Corvette box would stay correct without a chance of an error. It would also save a fair bit of work I would presume.
So once the sandwich plate and the shaft was modified, that leaves the ring and pinion. The existing Corvette ratios do not suit the use of any of the 928's current ratios. So a new ring and pinion would need to be made. That is no big deal as a manufacturer in Australia already makes the crown wheel in various ratios and a custom or read 928 pinion to suit that high ratio crown wheel would need to be manufactured.
The cost for the Albins ring and pinion as they are sold now is around $2,500 per set. Obviously a custom part would be a bit more depending on quantities. They make Porsche Cup car parts and the V8 Supercar sequential transmissions, much like Holinger and Emco. So they could certainly make that part very nicely indeed.
By using the 928 diff housing, that allows the use of the standard or solid aftermarket mounts and bolts simply to the rear crossmember. It would make keeping the car easily registerable, that is by keeping those parts standard an engineering certificate would most likely not be needed, folks from my part of the world would understand that, it is an important point. It is also a potential insurance issue too, whereas a different transmission is not the same as changing the suspension design or pickup points.
Albins can also make custom driveshafts, if that was looked at I would have one shaft made around 20% thicker than the other side to avoid the axle tramp that the 928 gets. You could probably use the same CV joints but with just a thicker driveshaft.
Now the sexier part of this conversion would be the carbon fibre driveshaft that are available, that is torque tube driveshaft. An exact measurement would need to be done but a small change of length wouldn't be out out the question. For the racers like Mike with a Motec, the ability to run without a worry a proper ignition cut for the traction control would be a definite advantage.
I wouldn't run the traction control with ignition cut with the standard 928 driveshaft as I believe it would turn it into a pile of metal splinters, much like what happens with the failures of one of the coils. The carbon shafts are very light at around 2 kgs and the Corvette housing is made from alloy so it would be a power and weight advantage.
For those thinking CF torque tube shafts are mega bucks, they range from $1,700 to $2,000 and are capable of over 800 HP. The interesting thing is that by using this conversion package, we may be able to get away from the 928s other high HP bug bear, the clutch.
I suppose it is not just a bug bear but parts are expensive and hard to get also. The ZR1 parts are rated for some pretty incredible numbers and work much the same way as the 928 parts. Think about it, doing away with the little Porsche intermediate shaft that costs $500 these days and I suspect only getting more expensive can't be a bad thing can it.
My guesstimate on the costing of this conversion doing it yourself would go something like $3,500 for transmission, $3,000 for the crown and pinion, $3,000 for the CF driveshaft and second hand torque tube housing, $2,000 for the clutch part. $3,000 for the sandwich plate and machined output shaft with a modified shifter mechanism and associated custom changes. So around $15K to make a reliable package with new parts.
That isn't too bad when you consider what a big change that is and how much money gets spent on the rest of the car, a good paint job can cost more than that here. Hope this idea helps the fraternity.
https://rennlist.com/forums/928-foru...ing-video.html
I have to say that I been sitting on this idea for quite some time, given my current predicament with my health it is not likely to get done by me and after Mike's trans failure given all his mighty efforts with the 928 it has made me go public with this idea as it is right up his alley.
While some research would still need to be undertaken regarding some fitment issues, these issues I can't see putting a stop to this idea. So the concept of a Corvette ZR1 (TR6060) box is not entirely new, as Aspkiller certainly has proved. Cudos to him for his achievements too
There is a more than one way to skin a cat. (hope my mum never reads that) The use of the ZR1 box is a good idea on many fronts, it is a cheap box to buy new or used. There is lots of good parts available to upgrade it and it is exceptionally strong, there is a choice of top gear ratios depending on the box sought, either performance or economy. There is also good parts with the associated driveline available, more on that later.
Nothing new there, how to go about implementing it? We are lucky that Porsche inadvertently gave us an option when they built the auto transmission. The fact that the rear housing for the differential unbolts like the Corvette is the real bonus. There is a sandwich plate that mates the ZF auto to the diff and this could be done with the Corvette manual and auto transmissions if one desired that.
The Corvette output shaft is quite beefy, in fact big enough to be cut down to the Porsche 928 output shaft size. The question I have there, is that I don't know enough about cutting that type of material. I don't believe it has been hardened in the area where, it would need shortening, two, the splines and threads would need cutting. Normally with the gearbox and driveshafts that I have seen the splines are the only area heat treated and hardened.
Cutting down and modifying the existing output shaft would have some advantages over making a part from scratch, as all the measurements internally in the Corvette box would stay correct without a chance of an error. It would also save a fair bit of work I would presume.
So once the sandwich plate and the shaft was modified, that leaves the ring and pinion. The existing Corvette ratios do not suit the use of any of the 928's current ratios. So a new ring and pinion would need to be made. That is no big deal as a manufacturer in Australia already makes the crown wheel in various ratios and a custom or read 928 pinion to suit that high ratio crown wheel would need to be manufactured.
The cost for the Albins ring and pinion as they are sold now is around $2,500 per set. Obviously a custom part would be a bit more depending on quantities. They make Porsche Cup car parts and the V8 Supercar sequential transmissions, much like Holinger and Emco. So they could certainly make that part very nicely indeed.
By using the 928 diff housing, that allows the use of the standard or solid aftermarket mounts and bolts simply to the rear crossmember. It would make keeping the car easily registerable, that is by keeping those parts standard an engineering certificate would most likely not be needed, folks from my part of the world would understand that, it is an important point. It is also a potential insurance issue too, whereas a different transmission is not the same as changing the suspension design or pickup points.
Albins can also make custom driveshafts, if that was looked at I would have one shaft made around 20% thicker than the other side to avoid the axle tramp that the 928 gets. You could probably use the same CV joints but with just a thicker driveshaft.
Now the sexier part of this conversion would be the carbon fibre driveshaft that are available, that is torque tube driveshaft. An exact measurement would need to be done but a small change of length wouldn't be out out the question. For the racers like Mike with a Motec, the ability to run without a worry a proper ignition cut for the traction control would be a definite advantage.
I wouldn't run the traction control with ignition cut with the standard 928 driveshaft as I believe it would turn it into a pile of metal splinters, much like what happens with the failures of one of the coils. The carbon shafts are very light at around 2 kgs and the Corvette housing is made from alloy so it would be a power and weight advantage.
For those thinking CF torque tube shafts are mega bucks, they range from $1,700 to $2,000 and are capable of over 800 HP. The interesting thing is that by using this conversion package, we may be able to get away from the 928s other high HP bug bear, the clutch.
I suppose it is not just a bug bear but parts are expensive and hard to get also. The ZR1 parts are rated for some pretty incredible numbers and work much the same way as the 928 parts. Think about it, doing away with the little Porsche intermediate shaft that costs $500 these days and I suspect only getting more expensive can't be a bad thing can it.
My guesstimate on the costing of this conversion doing it yourself would go something like $3,500 for transmission, $3,000 for the crown and pinion, $3,000 for the CF driveshaft and second hand torque tube housing, $2,000 for the clutch part. $3,000 for the sandwich plate and machined output shaft with a modified shifter mechanism and associated custom changes. So around $15K to make a reliable package with new parts.
That isn't too bad when you consider what a big change that is and how much money gets spent on the rest of the car, a good paint job can cost more than that here. Hope this idea helps the fraternity.
03-12-2012, 09:42 AM
#2
Three Wheelin'
I'm all ears, thanks for posting this. I hope your health improves.
Would this require cutting the floor/tunnel? That would put me out of the competative class.
Where are these cheap "ZR1" transaxles? I get the impression that the 'Vette is like a 928 in that there are a bunch of autos with manuals being rare.
Would this require cutting the floor/tunnel? That would put me out of the competative class.
Where are these cheap "ZR1" transaxles? I get the impression that the 'Vette is like a 928 in that there are a bunch of autos with manuals being rare.
03-12-2012, 10:37 AM
#3
Drifting
ZR1/Z06/Z07 only come in a manual. They aren't cheap though.
What Aspkiller did makes the most sense to me. Trying to keep the 928 diff and making custom gears is way more expensive than redoing the rear subframe mounts and custom half shafts. Also, the Vette diff is stronger so putting a "custom" weaker 928 diff behind the 6060 trans makes no sense to me.
What Aspkiller did makes the most sense to me. Trying to keep the 928 diff and making custom gears is way more expensive than redoing the rear subframe mounts and custom half shafts. Also, the Vette diff is stronger so putting a "custom" weaker 928 diff behind the 6060 trans makes no sense to me.
03-12-2012, 11:59 AM
#4
Race Director
keep in mind the emco sequential that Larry runs is the exact same size as a standard 6 speed vette transaxle....
Larry did test fit the 6 speed transaxle and it fit with mods.....
Rockland Standard Gear sells "tranzilla" based the older T56....it will hold 1000hp....I talked to them a while back and they said they have a C5 transaxle that will hold 850hp.....they also thought they could make new internals for 928 boxes....which is a good solution too...
Doc brought up great points about how everyone that races 928's uses USED gear boxes....purely for cost reasons...but they are at best 17 years old, possibly 30+.....probably with lots of easy miles too...asking a barely strong enough trans to handle 450ftlbs with slicks on well worn internals...of course they fail....
I do think the automatic is FAR stronger.....zero complaints with mine after 93 hours on track
Larry did test fit the 6 speed transaxle and it fit with mods.....
Rockland Standard Gear sells "tranzilla" based the older T56....it will hold 1000hp....I talked to them a while back and they said they have a C5 transaxle that will hold 850hp.....they also thought they could make new internals for 928 boxes....which is a good solution too...
Doc brought up great points about how everyone that races 928's uses USED gear boxes....purely for cost reasons...but they are at best 17 years old, possibly 30+.....probably with lots of easy miles too...asking a barely strong enough trans to handle 450ftlbs with slicks on well worn internals...of course they fail....
I do think the automatic is FAR stronger.....zero complaints with mine after 93 hours on track
03-12-2012, 02:36 PM
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I can't see 928 original box case being very good option no matter how much gears are made stronger. Its just simpler to make whole new casing which is not as weak design from a start. Take some really strong gears from where ever and make all new case for them which fits into available space. If some available 928 auto diff gearing works with custom box setup even better.
03-12-2012, 02:41 PM
#7
Drifting
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03-12-2012, 08:32 PM
#8
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I'm all ears, thanks for posting this. I hope your health improves.
Would this require cutting the floor/tunnel? That would put me out of the competative class.
Where are these cheap "ZR1" transaxles? I get the impression that the 'Vette is like a 928 in that there are a bunch of autos with manuals being rare.
Would this require cutting the floor/tunnel? That would put me out of the competative class.
Where are these cheap "ZR1" transaxles? I get the impression that the 'Vette is like a 928 in that there are a bunch of autos with manuals being rare.
03-12-2012, 08:49 PM
#9
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ZR1/Z06/Z07 only come in a manual. They aren't cheap though.
What Aspkiller did makes the most sense to me. Trying to keep the 928 diff and making custom gears is way more expensive than redoing the rear subframe mounts and custom half shafts. Also, the Vette diff is stronger so putting a "custom" weaker 928 diff behind the 6060 trans makes no sense to me.
What Aspkiller did makes the most sense to me. Trying to keep the 928 diff and making custom gears is way more expensive than redoing the rear subframe mounts and custom half shafts. Also, the Vette diff is stronger so putting a "custom" weaker 928 diff behind the 6060 trans makes no sense to me.
The ZR1 diff is a different matter, it has been heavily reninforced due to the previous failures. We don't see 928 diff housings flying apart and dumping their load. It has to do with it's design not it's relatively heavy casting in my opinion.
For myself and I think others, most can handle the idea of swapping out the parts that have become either NLA, or not up to current power outputs. However they would like to retain key 928 features like the Weisach rear end, the axles and the standard Porsche wheels etc..
Part of the strength of the new 928 rear end will come from the quality of the components, like the crown wheel and pinion made by Albins Gears. Lots of race parts don't break but wear out, I think the amount of gear area in the 928 differential is adequate for one, not breaking and having quite a long life.
03-12-2012, 08:54 PM
#10
Race Director
I can't agree John, the diff in the corvette prior to the ZR1 was never as strong as the 928 diff. There is more corvette diffs strewn over the race track than there is 928 engines that have done their rod bearings. There is upgrade kits sold just to try and keep them together.
The ZR1 diff is a different matter, it has been heavily reninforced due to the previous failures. We don't see 928 diff housings flying apart and dumping their load. It has to do with it's design not it's relatively heavy casting in my opinion.
For myself and I think others, most can handle the idea of swapping out the parts that have become either NLA, or not up to current power outputs. However they would like to retain key 928 features like the Weisach rear end, the axles and the standard Porsche wheels etc..
Part of the strength of the new 928 rear end will come from the quality of the components, like the crown wheel and pinion made by Albins Gears. Lots of race parts don't break but wear out, I think the amount of gear area in the 928 differential is adequate for one, not breaking and having quite a long life.
The ZR1 diff is a different matter, it has been heavily reninforced due to the previous failures. We don't see 928 diff housings flying apart and dumping their load. It has to do with it's design not it's relatively heavy casting in my opinion.
For myself and I think others, most can handle the idea of swapping out the parts that have become either NLA, or not up to current power outputs. However they would like to retain key 928 features like the Weisach rear end, the axles and the standard Porsche wheels etc..
Part of the strength of the new 928 rear end will come from the quality of the components, like the crown wheel and pinion made by Albins Gears. Lots of race parts don't break but wear out, I think the amount of gear area in the 928 differential is adequate for one, not breaking and having quite a long life.
I can name numerous race 928 failures....TT, engines, trans (typically 3rd or 5th gear)... not a single rear end or half shaft failure....
Then again they say the automatic isn't that strong...granted I don't have lots of power....but it runs great....plenty of ORR guys have zero issues....
03-12-2012, 08:54 PM
#11
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I can't see 928 original box case being very good option no matter how much gears are made stronger. Its just simpler to make whole new casing which is not as weak design from a start. Take some really strong gears from where ever and make all new case for them which fits into available space. If some available 928 auto diff gearing works with custom box setup even better.
This is a link to one of the carbon shafts that is available.
http://forums.corvetteforum.com/c5-t...ive-shaft.html
03-12-2012, 11:45 PM
#12
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ZR1/Z06/Z07 only come in a manual. They aren't cheap though.
What Aspkiller did makes the most sense to me. Trying to keep the 928 diff and making custom gears is way more expensive than redoing the rear subframe mounts and custom half shafts. Also, the Vette diff is stronger so putting a "custom" weaker 928 diff behind the 6060 trans makes no sense to me.
What Aspkiller did makes the most sense to me. Trying to keep the 928 diff and making custom gears is way more expensive than redoing the rear subframe mounts and custom half shafts. Also, the Vette diff is stronger so putting a "custom" weaker 928 diff behind the 6060 trans makes no sense to me.
http://www.gmhightechperformance.com...n/viewall.html
03-15-2012, 10:39 AM
#13
Three Wheelin'
Anyone have a 928 auto pinion gear to measure?
The spline size would be good to know.
I'm thinking of mounting a 928 auto diff to another trans per Slate's idea but not a Vette box.
The spline size would be good to know.
I'm thinking of mounting a 928 auto diff to another trans per Slate's idea but not a Vette box.
03-15-2012, 11:34 AM
#14
Drifting
For myself and I think others, most can handle the idea of swapping out the parts that have become either NLA, or not up to current power outputs. However they would like to retain key 928 features like the Weisach rear end, the axles and the standard Porsche wheels etc.
John and others these issues are what I am talking about in regard to the corvette diff.
http://www.gmhightechperformance.com...n/viewall.html
http://www.gmhightechperformance.com...n/viewall.html
C6 Z06 ring gear: 8.75"
928 ring gear: 8.5"?
I don't know what the ZR1 diff is, but it's stronger than the Z06. I think the diff itself is $4000 on top of the cost of the trans.
Last edited by 123quattro; 03-15-2012 at 11:56 AM.
03-15-2012, 12:41 PM
#15
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Anyone have a 928 auto pinion gear to measure?