LSD Differential/final drive specs & possible group purchase
01-16-2004, 03:15 PM
#31
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Hacker-Pschorr,
Jack up the rear w/both wheels off the ground. Spin on wheel, and see if the other wheel spins in the same direction. If this occurs, you have limited slip diff.
If it spins opposite, you have an open diff.
BC,
My intentions are to find a suitable aftermarket LS differential. I have no intentions on finding a final drive replacement. Though I find the idea of changing the final drive intriguing, it is not within my scope on this project. (could become a joint project?)
It seems others have changed final drives in the past, so hopefully they will post about their experiences.
Jack up the rear w/both wheels off the ground. Spin on wheel, and see if the other wheel spins in the same direction. If this occurs, you have limited slip diff.
If it spins opposite, you have an open diff.
BC,
My intentions are to find a suitable aftermarket LS differential. I have no intentions on finding a final drive replacement. Though I find the idea of changing the final drive intriguing, it is not within my scope on this project. (could become a joint project?)
It seems others have changed final drives in the past, so hopefully they will post about their experiences.
01-16-2004, 03:35 PM
#32
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Ok, I guess I should have been more specific! How about without jacking up the car?
01-16-2004, 04:44 PM
#33
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steve...comments " .................. Bad Santa replies
.......
2. There was an article in Excellence magazine about JK Crumb's new ring and pinion set purchased at GT Transmissions some 3-4 years ago. I have been considering this non-engine change because would like to improve Street Power (torque) by sacrificing 160 mph top speed. ....." ...........................BS , That ring and pinion will not fit an automatic
3. I believe the LSD unit (or standard) bolts to the ring gear making ratio a separate issue from slip........................BS , .Correct two very different issues
4. Jim b (here is a perfect opportunity to sell) having searched the Intl. site for "slip" have found used split 78-82 @ $650 (new and 83-89 @ $1000.)
New: 78-82 @ $3,521, 83-89 $2,436 and 90-95 $1,495. Will the 90-95 not work with older" .............BS . Correct the 90-95 have computer controlled PSD it has a hydraulic pump and slave cylinder operating a clutch inside the differential case it will not fit the early cars .... , where is the 40/80 split. ............BS .The change occurred for USAs cars with beginning of 1983 (euro cars was 1986 as I recall ) what is the torque capacity of each? ...?? good question ...........May I use the $1495 unit in my 86.5 S3? ........." B S , no !
5. If R&P are separate from slip what ratios are available and what combinations fit various years? .........BS .the 4 speed automatics offered a ratio of 33:15 (2.20), 33:13(2.357) , 33:14 ( 2.538) , the 3 speed autos were 33:12 (2.75) there are numerous differences between the 3 spd and 4 speed ring and pinions as well as the limited slip SO ....4 speeds can only use 4 speed gears ....2:20 , 2.37 and probably 2.538 ........BUT there is more to the story the 3 speed first gear ratio is 2.306 times the 2.75 final drive is 6.34 , the 4 speed with 2:20 final drive uses a 3.676 first gear for a 8.08 effective drive ratio . Second gear for the 4 speed is a 2.412 times the 2:20 for an effective ratio of 5.32 . (perhaps this is why Porsche opted to have later 4 speeds start in second ? ) First gear on a early 5 speed is a 10.22 ...........top gear is always 1.1 so final drive ratio is the effective 2:20 etc. engine turns 2.2 times wheel turns one time . Also why B S runs 225x50x15 yes 15 inch rims when playing racer that gives me "lower " gears as well as a lower car ; on the street the rears are 275x40x17 BUT are much taller hence larger diameter and one revolution covers more ground .
BS.. somehow the math Looks funny but I think it is correct
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.......
2. There was an article in Excellence magazine about JK Crumb's new ring and pinion set purchased at GT Transmissions some 3-4 years ago. I have been considering this non-engine change because would like to improve Street Power (torque) by sacrificing 160 mph top speed. ....." ...........................BS , That ring and pinion will not fit an automatic
3. I believe the LSD unit (or standard) bolts to the ring gear making ratio a separate issue from slip........................BS , .Correct two very different issues
4. Jim b (here is a perfect opportunity to sell) having searched the Intl. site for "slip" have found used split 78-82 @ $650 (new and 83-89 @ $1000.)
New: 78-82 @ $3,521, 83-89 $2,436 and 90-95 $1,495. Will the 90-95 not work with older" .............BS . Correct the 90-95 have computer controlled PSD it has a hydraulic pump and slave cylinder operating a clutch inside the differential case it will not fit the early cars .... , where is the 40/80 split. ............BS .The change occurred for USAs cars with beginning of 1983 (euro cars was 1986 as I recall ) what is the torque capacity of each? ...?? good question ...........May I use the $1495 unit in my 86.5 S3? ........." B S , no !
5. If R&P are separate from slip what ratios are available and what combinations fit various years? .........BS .the 4 speed automatics offered a ratio of 33:15 (2.20), 33:13(2.357) , 33:14 ( 2.538) , the 3 speed autos were 33:12 (2.75) there are numerous differences between the 3 spd and 4 speed ring and pinions as well as the limited slip SO ....4 speeds can only use 4 speed gears ....2:20 , 2.37 and probably 2.538 ........BUT there is more to the story the 3 speed first gear ratio is 2.306 times the 2.75 final drive is 6.34 , the 4 speed with 2:20 final drive uses a 3.676 first gear for a 8.08 effective drive ratio . Second gear for the 4 speed is a 2.412 times the 2:20 for an effective ratio of 5.32 . (perhaps this is why Porsche opted to have later 4 speeds start in second ? ) First gear on a early 5 speed is a 10.22 ...........top gear is always 1.1 so final drive ratio is the effective 2:20 etc. engine turns 2.2 times wheel turns one time . Also why B S runs 225x50x15 yes 15 inch rims when playing racer that gives me "lower " gears as well as a lower car ; on the street the rears are 275x40x17 BUT are much taller hence larger diameter and one revolution covers more ground .
BS.. somehow the math Looks funny but I think it is correct
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01-18-2004, 12:02 PM
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Hey, Jim, do you know-- would a 2.73 (GT) pinion shaft fit an '86 (2.20) tranny and gears?
I'd almost rather just have new gears cut, but having 5th gear at 1:1 would make for a severe overdrive. I'd rather have the '86.5 geared for about 165-170 mph top speed than it's current 212 mph gearing.
I'd almost rather just have new gears cut, but having 5th gear at 1:1 would make for a severe overdrive. I'd rather have the '86.5 geared for about 165-170 mph top speed than it's current 212 mph gearing.
01-18-2004, 12:13 PM
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Originally posted by Steve_C
...having searched the Intl. site for "slip" have found used split 78-82 @ $650 (new and 83-89 @ $1000.)
New: 78-82 @ $3,521, 83-89 $2,436 and 90-95 $1,495. Will the 90-95 not work with older, where is the 40/80 split. what is the torque capacity of each? May I use the $1495 unit in my 86.5 S3?
...having searched the Intl. site for "slip" have found used split 78-82 @ $650 (new and 83-89 @ $1000.)
New: 78-82 @ $3,521, 83-89 $2,436 and 90-95 $1,495. Will the 90-95 not work with older, where is the 40/80 split. what is the torque capacity of each? May I use the $1495 unit in my 86.5 S3?
You might also consider getting a used diff and having it rebuilt. I bought a "lightly used" LSD from a vendor. It was determined that "lightly used" was the vernacular used by some when they mean "spent." So my mechanic rebuilt it for me. It turns out that one can adjust the behavior of the limited slip diff by using different thickness plates. My '86.5 now has a limited slip diff that I would estimate is easily somewhere north of 60%--I track and autocross the car. Because of the diff I can say it has 917 go-fast parts.
01-19-2004, 11:08 PM
#37
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dont worry, i do understand the gearing physics. this quote from the handbook is correct, but the operative term is " over a given speed". so, please re read my post and you can see the gearing trade offs that dont nessesarily give more acclerative power. just efficiency of that power to the ground. Just keep in mind that the overall transmission ratio is to be looked at, and forget about thinking a ring and pinion change is doing very much. a great example of this is the 3:09. basically, it makes a GTS gear box, an S4 gear box for all practical purposes. if you can understand why, you have broken the code.
(ie 3:09 max speed in 5th is 145mph, and that is the same as the S4 in 4th gear. below that the gears have close to the same spacing, until 1st, which is basically useless. so there is no gain in acclerative torque at any given speed except 0-25mph, and a 6.5 liter in 1st gear could keep up with this slight advantage which is far more tire compound dependant and technique dependant than the gear adavantage in this one gear)
dont get caught up with " better torque in any gear" because of the obvious trade offs. yes, better torque, but remeber, the earlier shift, alows the same car with the taller ratios to have 20% better torque until it shifts into the next gear where it has the 10% disadvantage . Point is, its a series of trade offs. Just find the gear box , if the spacing is the same among gears, as it is in most 928s, and see if you can get near red line for most of the straights on a race course. dont get caught up in the numerical gear. Look at the final drive ratios.
Mk
(ie 3:09 max speed in 5th is 145mph, and that is the same as the S4 in 4th gear. below that the gears have close to the same spacing, until 1st, which is basically useless. so there is no gain in acclerative torque at any given speed except 0-25mph, and a 6.5 liter in 1st gear could keep up with this slight advantage which is far more tire compound dependant and technique dependant than the gear adavantage in this one gear)
dont get caught up with " better torque in any gear" because of the obvious trade offs. yes, better torque, but remeber, the earlier shift, alows the same car with the taller ratios to have 20% better torque until it shifts into the next gear where it has the 10% disadvantage . Point is, its a series of trade offs. Just find the gear box , if the spacing is the same among gears, as it is in most 928s, and see if you can get near red line for most of the straights on a race course. dont get caught up in the numerical gear. Look at the final drive ratios.
Mk
Originally posted by worf928
I know that I'm going to regret this...
MK, I quote from the Bosch Automotive Handbook:
"The higher the engine torque and overall transmission ratio between engine and driven wheels, and the lower the power-transmission losses, the higher is the motive force available at the drive wheels."
Non-traction-limited acceleration is directly related to available torque and how you are multiplying or dividing that torque via the gearbox. A higher overall ratio will allow for faster acceleration at a given speed in the same gear versus a lower ratio.
A higher final drive might not 'buy' you faster lap times at every track due exactly to the reasons you describe. But, it will generate more power at the wheels at any speed in any gear. For a high-power car like Mark's and assuming that he's using all of fifth gear - (Hey? Mark, do you see rev-limited top speed in 5th gear (170mph?) on any straight?) - a higher final drive may not be the appropriate place to sink dollars.
However, for the horsepower challenged, it might be.
The was a Pano article written by a Howard Jacobs in around 1999 about his switch to the 3.09. I looked briefly for it but couldn't find it.
I know that I'm going to regret this...
MK, I quote from the Bosch Automotive Handbook:
"The higher the engine torque and overall transmission ratio between engine and driven wheels, and the lower the power-transmission losses, the higher is the motive force available at the drive wheels."
Non-traction-limited acceleration is directly related to available torque and how you are multiplying or dividing that torque via the gearbox. A higher overall ratio will allow for faster acceleration at a given speed in the same gear versus a lower ratio.
A higher final drive might not 'buy' you faster lap times at every track due exactly to the reasons you describe. But, it will generate more power at the wheels at any speed in any gear. For a high-power car like Mark's and assuming that he's using all of fifth gear - (Hey? Mark, do you see rev-limited top speed in 5th gear (170mph?) on any straight?) - a higher final drive may not be the appropriate place to sink dollars.
However, for the horsepower challenged, it might be.
The was a Pano article written by a Howard Jacobs in around 1999 about his switch to the 3.09. I looked briefly for it but couldn't find it.
01-19-2004, 11:14 PM
#38
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problem is, if you bring the 220mph 2.2:1 ratio to a 2.75, you end up having to use the 50% drop 5th gear from 4th gear spread that will kill you!! better to leave the S4 gear box alone and use the 4th gear to 145, if you are racing. if cruising, and want to shift more, sure, going to a 2.75 will make the gear box very low.(1st gear very unusable) and the rest of the gears will be brough down to the 2.2 /2.75 percentage. (ie 1.25 / .8 )
which may not be that bad of a deal. depends on the track !
MK
which may not be that bad of a deal. depends on the track !
MK
Originally posted by SHRKBIT
Hey, Jim, do you know-- would a 2.73 (GT) pinion shaft fit an '86 (2.20) tranny and gears?
I'd almost rather just have new gears cut, but having 5th gear at 1:1 would make for a severe overdrive. I'd rather have the '86.5 geared for about 165-170 mph top speed than it's current 212 mph gearing.
Hey, Jim, do you know-- would a 2.73 (GT) pinion shaft fit an '86 (2.20) tranny and gears?
I'd almost rather just have new gears cut, but having 5th gear at 1:1 would make for a severe overdrive. I'd rather have the '86.5 geared for about 165-170 mph top speed than it's current 212 mph gearing.
01-20-2004, 12:21 AM
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Originally posted by mark kibort
dont worry,..
dont worry,..
a great example of this is the 3:09. basically, it makes a GTS gear box, an S4 gear box
I don't remember precisely - what's Mark using? He told me once at LRP but I forgot... Hanson's using a 2.72. Your ex-Holbert would have the 2.20 right?
I heard several reports of folks transitioning from the 2.20 to 2.72 box for DEs or other track events. And the opinion was rather uniform - the 2.72 rear was a good thing. In fact, a person of some repute in the 928 community hated his 2.72 box until he drove it on the track at Hallett at the first IOC. It was on the track that the box clicked for him and started making sense. I tend to agree - the 2.72 box isn't as right for cruising as the 2.20s are.
I'll still maintain that for the lower-power cars, for folks that do DEs or stock-class racing, for folks that have the 2.20 rear end, and for folks that just wanna lay down a long patch, that a ring switch might be worth considering.
01-20-2004, 12:30 PM
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Originally posted by mark kibort
problem is, if you bring the 220mph 2.2:1 ratio to a 2.75, you end up having to use the 50% drop 5th gear from 4th gear spread that will kill you!! better to leave the S4 gear box alone and use the 4th gear to 145, if you are racing. if cruising, and want to shift more, sure, going to a 2.75 will make the gear box very low.(1st gear very unusable) and the rest of the gears will be brough down to the 2.2 /2.75 percentage. (ie 1.25 / .8 )
problem is, if you bring the 220mph 2.2:1 ratio to a 2.75, you end up having to use the 50% drop 5th gear from 4th gear spread that will kill you!! better to leave the S4 gear box alone and use the 4th gear to 145, if you are racing. if cruising, and want to shift more, sure, going to a 2.75 will make the gear box very low.(1st gear very unusable) and the rest of the gears will be brough down to the 2.2 /2.75 percentage. (ie 1.25 / .8 )
Of course, I don't expect anyone to stick their neck out on this one unless they're pretty sure of the answer. I'll pester my mechanic about it.
01-20-2004, 12:37 PM
#41
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Curt .."Hey, Jim, do you know-- would a 2.73 (GT) pinion shaft fit an '86 (2.20) tranny and gears?" ........ Curt it would not the pinion shaft goes all the way through the transmission and there are numerous differences
in gears and bearings which all must fit the pinion shaft since it holds 1/2 of every gear set as well as the input 5 th gear . What WILL FIT is the Euro spec 1985-86 gear box G 28/10 which has the 2.727 ring and pinion .
in gears and bearings which all must fit the pinion shaft since it holds 1/2 of every gear set as well as the input 5 th gear . What WILL FIT is the Euro spec 1985-86 gear box G 28/10 which has the 2.727 ring and pinion .
01-20-2004, 12:48 PM
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Originally posted by Jim bailey - 928 International
What WILL FIT is the Euro spec 1985-86 gear box G 28/10 which has the 2.727 ring and pinion .
What WILL FIT is the Euro spec 1985-86 gear box G 28/10 which has the 2.727 ring and pinion .
01-20-2004, 06:12 PM
#43
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Actually, you are incorrect. the ratios of all the different rear end trannies are DIFFERENT. the S4 2.2 is different than the 2.2 of the '84, and the GT and the GTS have difffernt gears as well. Now, the reason for this is, the change in 2.75 vs the 2.2 is not as dramatic as the final drive ratios. Why? because the gear ratios are completely different.
what performace differences are you aware of?? the gear boxes are different, but the only REAL differences in performance of the GT vs the S4, is the 15hp of the engine! remember, (again) Anderson has not seen ANY improvement in his times in going from a 2.2 to a 2.75 GTS box. the syncros are stronger, and the ratios are different. However, there are subtle differences. AND , there are slight efficiency advantages for different tracks.
yes the 85 to 87 S4s had the same 2.2 ratios and the same trans ratios.
Im sticking my neck out. these are the real answers
MK
what performace differences are you aware of?? the gear boxes are different, but the only REAL differences in performance of the GT vs the S4, is the 15hp of the engine! remember, (again) Anderson has not seen ANY improvement in his times in going from a 2.2 to a 2.75 GTS box. the syncros are stronger, and the ratios are different. However, there are subtle differences. AND , there are slight efficiency advantages for different tracks.
yes the 85 to 87 S4s had the same 2.2 ratios and the same trans ratios.
Im sticking my neck out. these are the real answers
MK
Originally posted by SHRKBIT
Sorry, Mark, no sale! My 2.20 gearbox ratios differ from the GT gearbox only in final drive ratio. As I own one of each I'm well aware of the performance difference between the two. The GT's 2.7272... final drive ratio is a clear win for me, so the question is--still--does a 2.7272 GT pinion shaft fit my 86.5's 2.20 box (G28/11, I believe).
Of course, I don't expect anyone to stick their neck out on this one unless they're pretty sure of the answer. I'll pester my mechanic about it.
Sorry, Mark, no sale! My 2.20 gearbox ratios differ from the GT gearbox only in final drive ratio. As I own one of each I'm well aware of the performance difference between the two. The GT's 2.7272... final drive ratio is a clear win for me, so the question is--still--does a 2.7272 GT pinion shaft fit my 86.5's 2.20 box (G28/11, I believe).
Of course, I don't expect anyone to stick their neck out on this one unless they're pretty sure of the answer. I'll pester my mechanic about it.
01-20-2004, 06:28 PM
#44
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yes, you understand about the racing differences .
Actually, i did mean that the 3.09 on a GTS /GT/79 box will make a S4 gear box, less the 1st gear. meaning 2nd, 3rd 4th and 5th will be the same as the S4 1st 2nd 3rd and 4th. Also meaning, since both the new GTS 3.09 5th and the S4 4th gear max out at 150ish, and the spacing below is about the same (ie 1.33/.75) per gear change, there would be no difference in gears (or very little) from 30mph all the way to 150mph.
as far as laying rubber, expecially in the 6.5 liter category, this is no problem in 1st or second gear. having driven both, i can tell you the differences on the race track are very subtle.
Ive owned both gear boxes. for the tracks we drive, the 79 box (same or close to the GTS/GT ) is good too. there are trade offs. ive raced my 84 at that hp level and my 84 and now S4 at the same tracks. I can tell you from a racers perspective, its just about efficiency. keep in mind, Ive still run my stock 79 quite a bit faster than even Devek has with his 6.5 liter.
So, for somone to tell us that the 2.75 gear boxes are different than the 2.2's, they better have a better explanation than it just feels better. its pretty simple math here. again, it boils down to physics. gearing doesnt buy you HP (which is needed to accerlate a mass over a time and distance) it buys you the efficiency of the application of the rear wheel hp.
where you think you gain in one gear, you obviously will loose, for a proportionate amount of speed change, a proportional amount of torque.
The net of the gains can be 0 at certain target speeds. this can be in a drag race over a distance, or a straight away speed on a race track. Its not just about top speed of the car.
MK
Actually, i did mean that the 3.09 on a GTS /GT/79 box will make a S4 gear box, less the 1st gear. meaning 2nd, 3rd 4th and 5th will be the same as the S4 1st 2nd 3rd and 4th. Also meaning, since both the new GTS 3.09 5th and the S4 4th gear max out at 150ish, and the spacing below is about the same (ie 1.33/.75) per gear change, there would be no difference in gears (or very little) from 30mph all the way to 150mph.
as far as laying rubber, expecially in the 6.5 liter category, this is no problem in 1st or second gear. having driven both, i can tell you the differences on the race track are very subtle.
Ive owned both gear boxes. for the tracks we drive, the 79 box (same or close to the GTS/GT ) is good too. there are trade offs. ive raced my 84 at that hp level and my 84 and now S4 at the same tracks. I can tell you from a racers perspective, its just about efficiency. keep in mind, Ive still run my stock 79 quite a bit faster than even Devek has with his 6.5 liter.
So, for somone to tell us that the 2.75 gear boxes are different than the 2.2's, they better have a better explanation than it just feels better. its pretty simple math here. again, it boils down to physics. gearing doesnt buy you HP (which is needed to accerlate a mass over a time and distance) it buys you the efficiency of the application of the rear wheel hp.
where you think you gain in one gear, you obviously will loose, for a proportionate amount of speed change, a proportional amount of torque.
The net of the gains can be 0 at certain target speeds. this can be in a drag race over a distance, or a straight away speed on a race track. Its not just about top speed of the car.
MK
Originally posted by worf928
MK, I think we're on the same page here now. For road racing it is most definitely not a given that a final drive change is a big win - as I wrote. All factors need to be considered - power at the flywheel, gear spacing, typical track layout etc. My post was intended to disentangle the issues of the essential physics and the art (more like cubic dollars) of optimizing overall gear ratios for road-racing.
I think you meant "makes an S4 gear box a GTS box. (I checked the specs btw...)
I don't remember precisely - what's Mark using? He told me once at LRP but I forgot... Hanson's using a 2.72. Your ex-Holbert would have the 2.20 right?
I heard several reports of folks transitioning from the 2.20 to 2.72 box for DEs or other track events. And the opinion was rather uniform - the 2.72 rear was a good thing. In fact, a person of some repute in the 928 community hated his 2.72 box until he drove it on the track at Hallett at the first IOC. It was on the track that the box clicked for him and started making sense. I tend to agree - the 2.72 box isn't as right for cruising as the 2.20s are.
I'll still maintain that for the lower-power cars, for folks that do DEs or stock-class racing, for folks that have the 2.20 rear end, and for folks that just wanna lay down a long patch, that a ring switch might be worth considering.
MK, I think we're on the same page here now. For road racing it is most definitely not a given that a final drive change is a big win - as I wrote. All factors need to be considered - power at the flywheel, gear spacing, typical track layout etc. My post was intended to disentangle the issues of the essential physics and the art (more like cubic dollars) of optimizing overall gear ratios for road-racing.
I think you meant "makes an S4 gear box a GTS box. (I checked the specs btw...)
I don't remember precisely - what's Mark using? He told me once at LRP but I forgot... Hanson's using a 2.72. Your ex-Holbert would have the 2.20 right?
I heard several reports of folks transitioning from the 2.20 to 2.72 box for DEs or other track events. And the opinion was rather uniform - the 2.72 rear was a good thing. In fact, a person of some repute in the 928 community hated his 2.72 box until he drove it on the track at Hallett at the first IOC. It was on the track that the box clicked for him and started making sense. I tend to agree - the 2.72 box isn't as right for cruising as the 2.20s are.
I'll still maintain that for the lower-power cars, for folks that do DEs or stock-class racing, for folks that have the 2.20 rear end, and for folks that just wanna lay down a long patch, that a ring switch might be worth considering.
01-20-2004, 07:13 PM
#45
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Curt it gets a bit involved because as you mention the actual gear ratios of the pair of gears for 1 st 2nd 3rd 4 th ARE the same number of teeth BUT BIG BUT .. for all gears EXCEPT 5 th gear you also have a lay shaft gear ratio as part of the equation . The input shaft 5 th gear when in fifth simply drives the pinoin on which it rides at 1 to 1 . All other gears the power enters on 5th then transfers via the toothed gear down to the layshaft gear .............so the ratio of these two gears becomes part of the ratio for all gears except 5 th . The 2.20 box has a layshaft gear ratio of 33:21 while the 2.73 uses 32:22 . So first gear in a 2.73 box after multiplying by the layshaft ratio is 3.7645 which times 2.73 equals a final ratio of 10.27 . The 2.20 is 4.067 times 2.2 for a 8.94 first gear . So the Euro first gear is much lower than the USA but put the 2.73 into a USA... box and first becomes an 11.116 first gear even lower than the actual final ratio for the euro all the gear BUT fifth are pushed down . Then in the shift from 4 to 5 th you have the wider "gap" more RPM drop than normal . The reason the 5 th gears have a different part numbers Euro to USA is because of the lay shaft ratio . For drag racing where the launch is so important lower gears allows the engine to up in the high horsepower range quickly and do the work needed to put the mass of the car in motion , the down side is the need to shift sooner to avoid over reving the engine .