VETTE TRANNY INSTALLED-SOME TESTING RESULTS AT POST 157
04-28-2011, 08:50 PM
#151
Larry i was just looking at gear ratios and I know there may be a multitude of reasons for the choice of the C5 tranny however in the current ZR1 the ratios are now close and top gear is the gear that top speed is now attained in that car. I also understand when you do a job like this you may want to start off slow i.e not spend too much money until you are sure it can be done etc so don't look at this like it is a critisism. The ratio of the 5 and 6 gear for the ZR1 box is very close to the top gear in the GT box (5) and the american 2.20 box (6).
The ZR1 does have a very steep 1st gear which may make driving around town a bit better as 1st in the GT box is too low in my opinion. The first gear in the ZR1 is a bit shorter than 2nd in the GT box. The other thing is that box has been greatly strengthed and has numerous improvements for shift quality. Here's an interesting link.
http://forums.corvetteforum.com/auto...nsmission.html
Greg
The ZR1 does have a very steep 1st gear which may make driving around town a bit better as 1st in the GT box is too low in my opinion. The first gear in the ZR1 is a bit shorter than 2nd in the GT box. The other thing is that box has been greatly strengthed and has numerous improvements for shift quality. Here's an interesting link.
http://forums.corvetteforum.com/auto...nsmission.html
Greg
04-28-2011, 09:12 PM
#152
Three Wheelin'
My apologies, I was asking what parts of the rear end of the corvette are you using? Is it the whole cradle adapted to work, or just uprights? Having just come from the C5 crowd, I've got it relatively fresh in my mind what you may have used to adapt to the 928 from the corvette.
04-29-2011, 03:22 PM
#153
Rennlist Member
Thread Starter
Greg-
You got it exactly right. We used a c5 because it can handle all the power a stock LS motor (except a 7, maybe) can put out and it is reasonably available. That makes it the ideal candidate for stock 928s. As power increases, different and/or additional mods may be needed. Also, the type of driving makes a hugh difference in the ability of the components to handle the power. Standing starts with slicks probably puts the most strain on axles and differentials.
At about 700 crank hp/tq, we think a built z06 diff is probably essential, along with custom racing axles. Rem/cryo, temperature control and proper fluid will also help to keep parts alive. As to the ZR1 box, it is heavier and stronger, especially the ring gear. But I'm not sure it really is needed in our applications.
Jon B.-
On my car only, we are using a custom cradle, but everything else is Corvette or modified Corvette. I'm planning on using an EMCO box into a c6z Quaife diff.
For a production kit, the more that stays Porsche, the better. But a custom cradle and custom axles seem to be a given.
You got it exactly right. We used a c5 because it can handle all the power a stock LS motor (except a 7, maybe) can put out and it is reasonably available. That makes it the ideal candidate for stock 928s. As power increases, different and/or additional mods may be needed. Also, the type of driving makes a hugh difference in the ability of the components to handle the power. Standing starts with slicks probably puts the most strain on axles and differentials.
At about 700 crank hp/tq, we think a built z06 diff is probably essential, along with custom racing axles. Rem/cryo, temperature control and proper fluid will also help to keep parts alive. As to the ZR1 box, it is heavier and stronger, especially the ring gear. But I'm not sure it really is needed in our applications.
Jon B.-
On my car only, we are using a custom cradle, but everything else is Corvette or modified Corvette. I'm planning on using an EMCO box into a c6z Quaife diff.
For a production kit, the more that stays Porsche, the better. But a custom cradle and custom axles seem to be a given.
04-30-2011, 10:05 AM
#154
Greg-
You got it exactly right. We used a c5 because it can handle all the power a stock LS motor (except a 7, maybe) can put out and it is reasonably available. That makes it the ideal candidate for stock 928s. As power increases, different and/or additional mods may be needed. Also, the type of driving makes a hugh difference in the ability of the components to handle the power. Standing starts with slicks probably puts the most strain on axles and differentials.
At about 700 crank hp/tq, we think a built z06 diff is probably essential, along with custom racing axles. Rem/cryo, temperature control and proper fluid will also help to keep parts alive. As to the ZR1 box, it is heavier and stronger, especially the ring gear. But I'm not sure it really is needed in our applications.
Jon B.-
On my car only, we are using a custom cradle, but everything else is Corvette or modified Corvette. I'm planning on using an EMCO box into a c6z Quaife diff.
For a production kit, the more that stays Porsche, the better. But a custom cradle and custom axles seem to be a given.
You got it exactly right. We used a c5 because it can handle all the power a stock LS motor (except a 7, maybe) can put out and it is reasonably available. That makes it the ideal candidate for stock 928s. As power increases, different and/or additional mods may be needed. Also, the type of driving makes a hugh difference in the ability of the components to handle the power. Standing starts with slicks probably puts the most strain on axles and differentials.
At about 700 crank hp/tq, we think a built z06 diff is probably essential, along with custom racing axles. Rem/cryo, temperature control and proper fluid will also help to keep parts alive. As to the ZR1 box, it is heavier and stronger, especially the ring gear. But I'm not sure it really is needed in our applications.
Jon B.-
On my car only, we are using a custom cradle, but everything else is Corvette or modified Corvette. I'm planning on using an EMCO box into a c6z Quaife diff.
For a production kit, the more that stays Porsche, the better. But a custom cradle and custom axles seem to be a given.
http://forums.corvetteforum.com/c6-corvette-general-discussion/2255550-rear-differential-blown-pics.html
http://forums.corvetteforum.com/c6-t...e-housing.html
The later boxes were beefed up around the diff area, you can see the differences in this link. However despite our weak gearboxes we don't have exploding differential syndrome.
http://forums.corvetteforum.com/c6-c...wn-pics-2.html
This is an interesting thread, a modded version of the best gearbox the 6060 and then some serious mods done and for quite a reasonable price. The problems don't completely resolve if you read the posting. It is just transferred to a different area, the syncros.
http://forums.corvetteforum.com/auto...ad-racing.html
One things I was considering was to use the Porsche diff, that way the PSD can be retained and there is no problem with the axles connecting up. In the ZR1 the axles are different thicknesses 33 and 40 mm to help avoid axles hop. Don't know how that works, maybe via natural frequencies? Have you seen this thread? Maybe with a custom ring and pinion with higher gearing like 3.42 to 3.90?
http://928.landsharkoz.com/Forums/tabid/211/forumid/1/postid/468/view/topic/Default.aspx
04-30-2011, 12:04 PM
#155
Three Wheelin'
Greg,
It's pretty well known in the Corvette community that wheel hop kills the trans, actually, actually it will kill a trans period. There are other measures to control it, usually better shocks, the differing axle thickness, etc.
I still think, just like you do that this is the best option for our cars. I'd like like a 6060 over a T56 personally.
It's pretty well known in the Corvette community that wheel hop kills the trans, actually, actually it will kill a trans period. There are other measures to control it, usually better shocks, the differing axle thickness, etc.
I still think, just like you do that this is the best option for our cars. I'd like like a 6060 over a T56 personally.
05-17-2011, 09:06 PM
#156
Rennlist Member
Thread Starter
TRACT TESTING AND WHEEL HOP ISSUES
Keep in mind that I don't have a lot of seat time in this or any other similarly designed track/race car. So, my comments are just opinions and probably ought to be taken with a grain of salt and a couple of shots of Tequila.
Anyway, just got back from Thunderhill after a couple of days testing the c5 set-up and wheel hop was non-existent. We used custom axles into c5 uprights. The only real problem we found with our set-up was the inferior c5 single piston rear brakes. Burned up a set of front pads, as they were doing all the work stopping the car. We are now getting ready to put the S4 rear calipers back on the Vette uprights, using modified hats and rotors. Additionally, we will be putting on 355mm front rotors/clipers, although not an essential mod at this time. We've also decided to get rid of ABS. One of the toughest parts of the conversion was drilling the c5 hubs for 5x130 studs. Not enought material left on the hub. A little welding solved the problem temporarily.
Two major differences showed up with the Vette transaxle. First, shifting was more precise. While some might consider it to be a bit "notchy", I felt it was vastly better that the Porsche box. I tended to be a little careful going into fifth, due to the fact that we removed the reverse lock-out. Gear selection, up or down, just seemed much easier. Only had two missed shifts and both were 3rd to 4th, where I think I was pulling the shifter back into me and picked up a piece of 2nd.
Second, the stock c5 lsd was 1000 percent better than the PSD found in my 91, at least in on-track situations. Can't compare it to the LSD diff as I haven't any track experience with one.
Finally, the most dramatic change we experienced was turn-in. We modified the lower front control arms and built custom fully adjustable uppers that allowed us to run 3.5 degrees of camber, with even more negative available. We also used Delrin bushings in front on the lowers.
We are now trying to decide if our slow economic times merit the development and marketing of a c5 kit. Seems like car race / modification budgets are the first to get cut when things get tight. As they probably should.
Anyway, just got back from Thunderhill after a couple of days testing the c5 set-up and wheel hop was non-existent. We used custom axles into c5 uprights. The only real problem we found with our set-up was the inferior c5 single piston rear brakes. Burned up a set of front pads, as they were doing all the work stopping the car. We are now getting ready to put the S4 rear calipers back on the Vette uprights, using modified hats and rotors. Additionally, we will be putting on 355mm front rotors/clipers, although not an essential mod at this time. We've also decided to get rid of ABS. One of the toughest parts of the conversion was drilling the c5 hubs for 5x130 studs. Not enought material left on the hub. A little welding solved the problem temporarily.
Two major differences showed up with the Vette transaxle. First, shifting was more precise. While some might consider it to be a bit "notchy", I felt it was vastly better that the Porsche box. I tended to be a little careful going into fifth, due to the fact that we removed the reverse lock-out. Gear selection, up or down, just seemed much easier. Only had two missed shifts and both were 3rd to 4th, where I think I was pulling the shifter back into me and picked up a piece of 2nd.
Second, the stock c5 lsd was 1000 percent better than the PSD found in my 91, at least in on-track situations. Can't compare it to the LSD diff as I haven't any track experience with one.
Finally, the most dramatic change we experienced was turn-in. We modified the lower front control arms and built custom fully adjustable uppers that allowed us to run 3.5 degrees of camber, with even more negative available. We also used Delrin bushings in front on the lowers.
We are now trying to decide if our slow economic times merit the development and marketing of a c5 kit. Seems like car race / modification budgets are the first to get cut when things get tight. As they probably should.
05-17-2011, 09:59 PM
#157
Geez you got that job done quick, well done, can you elaborate on why the PSD was no good for you. Interesting write up.
Keep in mind that I don't have a lot of seat time in this or any other similarly designed track/race car. So, my comments are just opinions and probably ought to be taken with a grain of salt and a couple of shots of Tequila.
Anyway, just got back from Thunderhill after a couple of days testing the c5 set-up and wheel hop was non-existent. We used custom axles into c5 uprights. The only real problem we found with our set-up was the inferior c5 single piston rear brakes. Burned up a set of front pads, as they were doing all the work stopping the car. We are now getting ready to put the S4 rear calipers back on the Vette uprights, using modified hats and rotors. Additionally, we will be putting on 355mm front rotors/clipers, although not an essential mod at this time. We've also decided to get rid of ABS. One of the toughest parts of the conversion was drilling the c5 hubs for 5x130 studs. Not enought material left on the hub. A little welding solved the problem temporarily.
Two major differences showed up with the Vette transaxle. First, shifting was more precise. While some might consider it to be a bit "notchy", I felt it was vastly better that the Porsche box. I tended to be a little careful going into fifth, due to the fact that we removed the reverse lock-out. Gear selection, up or down, just seemed much easier. Only had two missed shifts and both were 3rd to 4th, where I think I was pulling the shifter back into me and picked up a piece of 2nd.
Second, the stock c5 lsd was 1000 percent better than the PSD found in my 91, at least in on-track situations. Can't compare it to the LSD diff as I haven't any track experience with one.
Finally, the most dramatic change we experienced was turn-in. We modified the lower front control arms and built custom fully adjustable uppers that allowed us to run 3.5 degrees of camber, with even more negative available. We also used Delrin bushings in front on the lowers.
We are now trying to decide if our slow economic times merit the development and marketing of a c5 kit. Seems like car race / modification budgets are the first to get cut when things get tight. As they probably should.
Anyway, just got back from Thunderhill after a couple of days testing the c5 set-up and wheel hop was non-existent. We used custom axles into c5 uprights. The only real problem we found with our set-up was the inferior c5 single piston rear brakes. Burned up a set of front pads, as they were doing all the work stopping the car. We are now getting ready to put the S4 rear calipers back on the Vette uprights, using modified hats and rotors. Additionally, we will be putting on 355mm front rotors/clipers, although not an essential mod at this time. We've also decided to get rid of ABS. One of the toughest parts of the conversion was drilling the c5 hubs for 5x130 studs. Not enought material left on the hub. A little welding solved the problem temporarily.
Two major differences showed up with the Vette transaxle. First, shifting was more precise. While some might consider it to be a bit "notchy", I felt it was vastly better that the Porsche box. I tended to be a little careful going into fifth, due to the fact that we removed the reverse lock-out. Gear selection, up or down, just seemed much easier. Only had two missed shifts and both were 3rd to 4th, where I think I was pulling the shifter back into me and picked up a piece of 2nd.
Second, the stock c5 lsd was 1000 percent better than the PSD found in my 91, at least in on-track situations. Can't compare it to the LSD diff as I haven't any track experience with one.
Finally, the most dramatic change we experienced was turn-in. We modified the lower front control arms and built custom fully adjustable uppers that allowed us to run 3.5 degrees of camber, with even more negative available. We also used Delrin bushings in front on the lowers.
We are now trying to decide if our slow economic times merit the development and marketing of a c5 kit. Seems like car race / modification budgets are the first to get cut when things get tight. As they probably should.
05-17-2011, 10:14 PM
#160
Drifting
Please consider a street conversion kit. If anything you could market it to increase gas mileage greatly. I for one would be interested for that reason alone. Some of us drive our 928's ALL the time. It is my ONLY vehicle.
05-17-2011, 10:15 PM
#161
Rennlist Member
Larry,
Why the 3.5 degrees of camber. are you running really soft springs? Anderson and I have found near 2 to be optimal up front.
Buring the brakes? thats odd. sounds like you might have had substandard pads up front.not much rear is not a big deal, especially at thunderhill.
any times? how fast were you hitting the main straight!????? 150??
cool! nice job on the conversion. more pictures.
Mark
Why the 3.5 degrees of camber. are you running really soft springs? Anderson and I have found near 2 to be optimal up front.
Buring the brakes? thats odd. sounds like you might have had substandard pads up front.not much rear is not a big deal, especially at thunderhill.
any times? how fast were you hitting the main straight!????? 150??
cool! nice job on the conversion. more pictures.
Mark
05-17-2011, 10:28 PM
#162
Archive Gatekeeper
Rennlist Member
Rennlist Member
Awesome job, Larry!
Now- I'll open the bidding for that crappy, raced, PSD-having G28.55 box, at $2500. Call me.
Now- I'll open the bidding for that crappy, raced, PSD-having G28.55 box, at $2500. Call me.
05-17-2011, 10:45 PM
#164
Drifting
I would say that you would be better off to offer the service of doing the conversion for those that want it.
The C5 trans is a stronger trans, that is a given, But
To stick a 928 body on a corvette dose not make the corvette a 928 (if you know what I mean)
The wheel base, the weight, the suspension, the feel, IMHO that is what I would call a 928 or corvette or jag, ect.
Please don't get me wrong as I am all for making things better, or at least stronger.
But when we have replaced everything on it to make it stronger, is it still a 928.
I commend you on a successful conversion.
Where are the pictures
Brad
The C5 trans is a stronger trans, that is a given, But
To stick a 928 body on a corvette dose not make the corvette a 928 (if you know what I mean)
The wheel base, the weight, the suspension, the feel, IMHO that is what I would call a 928 or corvette or jag, ect.
Please don't get me wrong as I am all for making things better, or at least stronger.
But when we have replaced everything on it to make it stronger, is it still a 928.
I commend you on a successful conversion.
Where are the pictures
Brad
05-17-2011, 10:57 PM
#165
Administrator - "Tyson"
Lifetime Rennlist
Member
Lifetime Rennlist
Member
To stick a 928 body on a corvette dose not make the corvette a 928 (if you know what I mean)
The wheel base, the weight, the suspension, the feel, IMHO that is what I would call a 928 or corvette or jag, ect.
Please don't get me wrong as I am all for making things better, or at least stronger.
But when we have replaced everything on it to make it stronger, is it still a 928.
I commend you on a successful conversion.
Where are the pictures
The wheel base, the weight, the suspension, the feel, IMHO that is what I would call a 928 or corvette or jag, ect.
Please don't get me wrong as I am all for making things better, or at least stronger.
But when we have replaced everything on it to make it stronger, is it still a 928.
I commend you on a successful conversion.
Where are the pictures
Lotus has historically made some of the best chassis in history from Indy, to F1 and the latest Elise. They've held almost every brand engine from Ford, Chevy, Cosworth, and now Toyota. God knows how many different transmissions.
They are all considered a Lotus. McLaren holds the same kind of history as goes Lola and a countless number of cars over the last century.
It's not our fault Porsche decided to go their arrogant ways with the 5-speed and designed their own versus buying a much stronger "off the shelf" unit back in 1978. Nobody has a problem with the Mercedes transmission in the auto's.....
Point is, what if Porsche had installed a "T-5" or some other generic 5-speed into the 928 and we were simply upgrading to a newer version, would the same question apply?
This is not a "Corvette" transmission, it's not made by GM. It just happens to be the same unit Chevrolet puts in their sports car
