S2 or 968 6 speed gearbox?
02-11-2005, 04:37 PM
#46
Race Director
Thread Starter
Obviously its easier, the shorter gears 3, 4, and 5 only are $675. But I still have a weaker gearbox and taller ratios in 1 and 2 than the S2 or 6 speed. And I only have one gearbox. If I get the S2 or 6 speed, I get a spare. By the sounds of it the only "worries" are getting the speedo working which some have done already... so there are not any.
Originally Posted by Z-man
To clarify - it is easier and cheaper to get custom gears for a 951 instead of retro-fitting a 968 sources 6-speed.
As stated above, you need the 968 1/2 axles since the right side (?) is shorter whereas the 951 half axles are the same length on both sides. But don't you also need a 968 torque tube? Isn't the 968 unit a 'split' tube or something like that? And then there is the speedo issues already mentioned.
If you get a custom gearset for the 951, you don't have any of the worries / issues that come up with the 968 tranny transplant.
Sixth gear would be nice on the highway to save fuel, but on the track it really doesn't help much - with my 944S2, I hardly ever get into 5th gear, so 6th would be overkill.
-Z-man.
As stated above, you need the 968 1/2 axles since the right side (?) is shorter whereas the 951 half axles are the same length on both sides. But don't you also need a 968 torque tube? Isn't the 968 unit a 'split' tube or something like that? And then there is the speedo issues already mentioned.
If you get a custom gearset for the 951, you don't have any of the worries / issues that come up with the 968 tranny transplant.
Sixth gear would be nice on the highway to save fuel, but on the track it really doesn't help much - with my 944S2, I hardly ever get into 5th gear, so 6th would be overkill.
-Z-man.
02-12-2005, 06:52 AM
#50
Drifting
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Hi Guys,
I was running through my Porsche Tech Spec handbook.
Apparently the only diff between the 951 & S2 box is the
R & P. The 951 having 8:27 while the 944S2 has a 8:31.
If this makes so much diff in accel, changing to the 944S
R & P would be even better 9:35
I was running through my Porsche Tech Spec handbook.
Apparently the only diff between the 951 & S2 box is the
R & P. The 951 having 8:27 while the 944S2 has a 8:31.
If this makes so much diff in accel, changing to the 944S
R & P would be even better 9:35
02-12-2005, 02:16 PM
#51
Three Wheelin'
Originally Posted by J Chen
Hi Guys,
I was running through my Porsche Tech Spec handbook.
Apparently the only diff between the 951 & S2 box is the
R & P. The 951 having 8:27 while the 944S2 has a 8:31.
If this makes so much diff in accel, changing to the 944S
R & P would be even better 9:35
I was running through my Porsche Tech Spec handbook.
Apparently the only diff between the 951 & S2 box is the
R & P. The 951 having 8:27 while the 944S2 has a 8:31.
If this makes so much diff in accel, changing to the 944S
R & P would be even better 9:35
The 944S2 tranny has a lower final drive than a 951 tranny and a taller fifth gear (36:28 = 0.778 versus 35:29 = 0.829 in a 951) to allow a bit more top end. First to fourth are identical. So the choices remain the 944S2 tranny, the 951 tranny; the 968 6-speed, mix and match 5th gear and R&P between the 944S2 and 951, and custom gears in any of the above.
Personally, I am staying with my 951S (AOR) tranny, which is the stongest of the 944 5-speeds, and having the differential/LSD rebuilt and seals/gaskets replaced.
02-12-2005, 02:41 PM
#52
Drifting
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Thanks for the info Waterguy. Funny that my Tech Spec
handbook states that the fifth gear for the 951 & S2 box
are the same. This brings up another question. It now
seems pointless to get to 400rwhp when the top speed
is being limited by the gearing. In a nutshell it would be
better if we can get a strong R & P of the S box & run with
300-350 rwhp. Yes a small sacrifice in top speed but !!!!!
handbook states that the fifth gear for the 951 & S2 box
are the same. This brings up another question. It now
seems pointless to get to 400rwhp when the top speed
is being limited by the gearing. In a nutshell it would be
better if we can get a strong R & P of the S box & run with
300-350 rwhp. Yes a small sacrifice in top speed but !!!!!
02-12-2005, 03:19 PM
#55
Race Director
Thread Starter
Roger Brown...
"Please review the attached gear charts. Using the S2 ring and pinion with
my short 3rd-5th is the absolute shortest combination possible-currently.
Regards,
Roger"
"Please review the attached gear charts. Using the S2 ring and pinion with
my short 3rd-5th is the absolute shortest combination possible-currently.
Regards,
Roger"
02-12-2005, 04:59 PM
#57
Race Director
Thread Starter
Yes it would, but you dont have to install the shorter 5th! I looked at the 951 box with shorter 3rd and 4th only, this means the 4th will top out at 200kph. Which would mean I get to see out 4th on the 1/4 mile. The S2 is desirable as its a stronger box! I would likely not install the shorter gears if i went to the S2 box, just a quaife LSD and be done with it.
02-16-2005, 04:25 PM
#58
Three Wheelin'
Okay, here we go again. I have experience with the 968 transmission in a 951. My car was an '87, with a 944 turbo S transmission and many other mods. It was an AX/Track car that also got about 8k miles per year on the street.
First: gearing. If you are gonna make a change, you need to understand how gearing works and where your car makes power. This is where a dyno chart and a gearing chart help. I have a friend that installed a 944S transmission (or S2-- I cannot remember which) in his track-only 951 car. At Laguna at the exit of turn 2, I'd be shifting up into third in my 951with the stock turbo S gearbox. He'd be going into fourth. His gears were packed tight and my guess is he would be screwed on a track with longer straights. Anyway, when thinking this through, remember that wheels and tires make a difference too. That is understand the diameter. Gearing charts take this into account. You have to think it through. On my car, I ran 275 Kumhos or Hoosiers on 17 inch dia., 12 inch wide Fikses. The tires were taller than the stock 245/45 16 Turbo S size. So that already affected my gearing before the change to the 968 transmission. Also remember that desired gearing is track dependent, so plan ahead for that as well.
Of course for a street car, it is not as complicated.
Next, differentials. I installed a Quaife. I regretted it due to rampant inside wheel spin coming out of slower speed corners. Milledge and others had warned me abou this, but it was worse than I expected. Quaifes like softer rear suspensions, like in my current 911 race car (350 bhp, 1950 lbs.). My 951 was VERY stiff which is one favored way for setting them up for many of my local tracks. The Quaife did not get along with my existing set-up. I sold the car before I got it sorted, but I was considering selling the Quaife and getting a conventional LSD. Remember: The 968 transmission will accept any diff that works in a G50. That means even the "exotic" Porsche Motorports LSD's like those in the factory race cars can be used. Some of those diffs are very sexy.
In terms of parts, you need to get the axles for a 968 because they have two different lengths, and both may be different from a stock 951 or 951 S. You can use the same CV's if they match the later spline pattern. YOU DO NOT NEED THE TORQUE TUBE from a 968. YOU DO NEED THE 968 shift rod.
In terms of the speedo, I posted about ths NUMEROUS times. My solution was based upon one taken in a car owned by a fellow that had KMR do the install. You need to pick up pulses with a magnetic sender. An abs hub and sender work fine. My car did not have abs as it was originally purchased by a racing driver who did not want abs. So I had to fabricate. I used a piece of metal glued to a CV joint, and a VDO magnetic pick up sender. The pulse signal needed to be converted to properly read on the speedo/odo. For that I used a product called an electronic ratio adapter. To calibrate, I used mileage markers on the freeway.
When I was finished, I was pleased with the change for the most part, except for the Quaife. I was either gonna replace it, or soften the car up to free things up. From a gearing standpoint, it was a positive change, based on my local tracks and where my engine made power (I had the 360 bhp Milledge setup).
I have additional details and pics if someone needs them.
When considering this change, you should consider the way the car is used. If it is used only for street driving, it is a more straightforward decision. If it is used on the track, plan carefully.
- Mike
First: gearing. If you are gonna make a change, you need to understand how gearing works and where your car makes power. This is where a dyno chart and a gearing chart help. I have a friend that installed a 944S transmission (or S2-- I cannot remember which) in his track-only 951 car. At Laguna at the exit of turn 2, I'd be shifting up into third in my 951with the stock turbo S gearbox. He'd be going into fourth. His gears were packed tight and my guess is he would be screwed on a track with longer straights. Anyway, when thinking this through, remember that wheels and tires make a difference too. That is understand the diameter. Gearing charts take this into account. You have to think it through. On my car, I ran 275 Kumhos or Hoosiers on 17 inch dia., 12 inch wide Fikses. The tires were taller than the stock 245/45 16 Turbo S size. So that already affected my gearing before the change to the 968 transmission. Also remember that desired gearing is track dependent, so plan ahead for that as well.
Of course for a street car, it is not as complicated.
Next, differentials. I installed a Quaife. I regretted it due to rampant inside wheel spin coming out of slower speed corners. Milledge and others had warned me abou this, but it was worse than I expected. Quaifes like softer rear suspensions, like in my current 911 race car (350 bhp, 1950 lbs.). My 951 was VERY stiff which is one favored way for setting them up for many of my local tracks. The Quaife did not get along with my existing set-up. I sold the car before I got it sorted, but I was considering selling the Quaife and getting a conventional LSD. Remember: The 968 transmission will accept any diff that works in a G50. That means even the "exotic" Porsche Motorports LSD's like those in the factory race cars can be used. Some of those diffs are very sexy.
In terms of parts, you need to get the axles for a 968 because they have two different lengths, and both may be different from a stock 951 or 951 S. You can use the same CV's if they match the later spline pattern. YOU DO NOT NEED THE TORQUE TUBE from a 968. YOU DO NEED THE 968 shift rod.
In terms of the speedo, I posted about ths NUMEROUS times. My solution was based upon one taken in a car owned by a fellow that had KMR do the install. You need to pick up pulses with a magnetic sender. An abs hub and sender work fine. My car did not have abs as it was originally purchased by a racing driver who did not want abs. So I had to fabricate. I used a piece of metal glued to a CV joint, and a VDO magnetic pick up sender. The pulse signal needed to be converted to properly read on the speedo/odo. For that I used a product called an electronic ratio adapter. To calibrate, I used mileage markers on the freeway.
When I was finished, I was pleased with the change for the most part, except for the Quaife. I was either gonna replace it, or soften the car up to free things up. From a gearing standpoint, it was a positive change, based on my local tracks and where my engine made power (I had the 360 bhp Milledge setup).
I have additional details and pics if someone needs them.
When considering this change, you should consider the way the car is used. If it is used only for street driving, it is a more straightforward decision. If it is used on the track, plan carefully.
- Mike
02-16-2005, 06:25 PM
#59
Burning Brakes
Originally Posted by Mahler9th
The pulse signal needed to be converted to properly read on the speedo/odo. For that I used a product called an electronic ratio adapter. To calibrate, I used mileage markers on the freeway
http://www.dakotadigital.com/Detail....-5/product.htm
btw...a Porsche ABS hub produces 45 pulses per wheel revolution. I believe the hall sender in the 951 transaxle produces 8 pulses per axle rev. if my math is right, 8 is 17.77% of 45.
