S2 ring & pinion
12-07-2007, 01:40 AM
#31
Rennlist Member
12-07-2007, 02:30 AM
#33
Rennlist Member
Join Date: Feb 2006
Location: Jackson, MS
Posts: 1,184
Likes: 0
Received 0 Likes
on
0 Posts
I have the S2 R/P in my turbo box I think, I like it for Auto X, but that think is screaming at 80: almost 4K rpm. If i understand correctly, can I put in the S2 5th gear and enjoy fast acceleration in 1-4 and a lower rpm 5th for highway?
12-07-2007, 02:51 AM
#34
IPSC
12-07-2007, 04:06 AM
#35
Rennlist Member
I think it's a question asked by someone else in this thread and I'm pretty sure you can. It's not a bad idea either as for hwy cruising the S2 conversion is a bit short in 5th.
12-07-2007, 09:25 AM
#36
Burning Brakes
Thread Starter
Join Date: Mar 2006
Location: Orlando,FL (formerly UK)
Posts: 1,215
Likes: 0
Received 0 Likes
on
0 Posts
Sorry Keith, nothing pointed at you, but that information is not correct. The reason to install the S2 R/P in the Turbo or Turbo S trans is because of the shorter final drive/faster acceleration. It is strong enough, but it is not stronger.
The ring gears are the same diameter, the Turbo has 27 teeth on it, the S2 has 31 teeth on it. Therefore the S2 gear teeth are smaller (and weaker), by approximately the same 15% difference in ratio. The pinions both have 8 teeth, but the Turbo pinion is larger in diameter and therefore the teeth are larger-beefier. I cannot understand how anyone that has looked at both components side by side, and has any basic metallurgy/engineering sense, could conclude anything other than the Turbo R/P is stronger.
The ring gears are the same diameter, the Turbo has 27 teeth on it, the S2 has 31 teeth on it. Therefore the S2 gear teeth are smaller (and weaker), by approximately the same 15% difference in ratio. The pinions both have 8 teeth, but the Turbo pinion is larger in diameter and therefore the teeth are larger-beefier. I cannot understand how anyone that has looked at both components side by side, and has any basic metallurgy/engineering sense, could conclude anything other than the Turbo R/P is stronger.
My understanding (incorrect or otherwise) was that the S2 was differently hardened in comparison to the 951S. -So I guess you're suggesting that this may not be the case.
One other question: Is 5th gear in a 951S higher than a regular 951, or the same ratio? -If it's a longer/taller ratio than the standard 951, is it by some chance the same as the S2? -or is the S2 5th gear ratio the "big, mean, tall... daddy of them all"?
Cheers,
Keith
12-07-2007, 10:25 AM
#37
Rennlist Member
Couple answers here:
Yes, all the parts, R/Ps, gear sets, bearings are interchangeable between the S, S2, and Turbo. The only one that is of concern is using the S R/P in a higher hp application, but they are physically interchangeable. Also, many of the N/A trans parts are also physically interchangeable, but may or may not be capable of handling higher power.
S2 5th is 0.778. Yes, this can also be installed in a Turbo trans (w/ or w/o the S2 R/P).
The North American 944 N/A 83-87 has a 0.730 5th (this is the tallest 5th available from the Porsche parts bin).
The 944S, Turbo, and Turbo S has the 0.829 5th. (Turbo, Turbo S, and Turbo Cup cars all have the same gearing and R/P).
The 0.829 5th with the Turbo 3.375 (the standard Turbo gearbox setup) is good for 171 at 6500, how much faster would you want to go? If you install an S2 .778 5th with the Turbo R/P, you could get a theoretical top speed of 182 at 6500, with the N/A .730 in a Turbo box, you could get 194 (but not sure the N/A 5th gear set is up to the task).
Keith, as far as the S2 R/P being harder than the others - couple things: hardening on gears is typically done for wear resistance on the teeth contact surfaces, not to strengthen it. If the teeth wear out prematurely or gaul/gouge up, you need a harder wear surface; if you break a tooth off, you need to make it bigger.
There is nothing published anywhere that indicates a different metallurgy or processing was used on the S2 R/P compared to the others - so its just pure speculation (guessing, made up).
Porsche could have used a magical hardening process on the S 3.889 R/P to make that harder/stronger, but instead they made the S2 3.875 R/P with fewer (and larger) teeth. They did that for a reason, and I recall its stated in the FSM that the S2 R/P was strengthened. Its in reference or comparison to the S transmission, but I think this may be the origin of the "S2 is the strongest" rumor - mechanics read that and think its in reference/comparison to the Turbo trans...
Yes, all the parts, R/Ps, gear sets, bearings are interchangeable between the S, S2, and Turbo. The only one that is of concern is using the S R/P in a higher hp application, but they are physically interchangeable. Also, many of the N/A trans parts are also physically interchangeable, but may or may not be capable of handling higher power.
S2 5th is 0.778. Yes, this can also be installed in a Turbo trans (w/ or w/o the S2 R/P).
The North American 944 N/A 83-87 has a 0.730 5th (this is the tallest 5th available from the Porsche parts bin).
The 944S, Turbo, and Turbo S has the 0.829 5th. (Turbo, Turbo S, and Turbo Cup cars all have the same gearing and R/P).
The 0.829 5th with the Turbo 3.375 (the standard Turbo gearbox setup) is good for 171 at 6500, how much faster would you want to go? If you install an S2 .778 5th with the Turbo R/P, you could get a theoretical top speed of 182 at 6500, with the N/A .730 in a Turbo box, you could get 194 (but not sure the N/A 5th gear set is up to the task).
Keith, as far as the S2 R/P being harder than the others - couple things: hardening on gears is typically done for wear resistance on the teeth contact surfaces, not to strengthen it. If the teeth wear out prematurely or gaul/gouge up, you need a harder wear surface; if you break a tooth off, you need to make it bigger.
There is nothing published anywhere that indicates a different metallurgy or processing was used on the S2 R/P compared to the others - so its just pure speculation (guessing, made up).
Porsche could have used a magical hardening process on the S 3.889 R/P to make that harder/stronger, but instead they made the S2 3.875 R/P with fewer (and larger) teeth. They did that for a reason, and I recall its stated in the FSM that the S2 R/P was strengthened. Its in reference or comparison to the S transmission, but I think this may be the origin of the "S2 is the strongest" rumor - mechanics read that and think its in reference/comparison to the Turbo trans...
12-07-2007, 11:13 AM
#38
Rennlist Member
Join Date: Feb 2006
Location: Jackson, MS
Posts: 1,184
Likes: 0
Received 0 Likes
on
0 Posts
So do you think the 5th out of an N/A would be able to handle a medium hp 951 power curve (i am rarely flooring it in 5th though, mostly would be just cruising highway use.
12-07-2007, 11:27 AM
#39
Burning Brakes
Thread Starter
Join Date: Mar 2006
Location: Orlando,FL (formerly UK)
Posts: 1,215
Likes: 0
Received 0 Likes
on
0 Posts
Great info, Jim!
I auto-cross in the 951S with the S2 R&P and it is indeed a great 'zoomer' in terms of acceleration. (-once the boost wakes up of course! ) but on the highway it is a little buzzy... almost down to 20MPH per thousand RPM.
These questions came mainly out of curiosity, and I'd partly assumed, partly guessed and possibly partly misinformed myself that the S2 swap was for durability rather than 're-gearing'.
I should be taking it to Sebring again next year and doing some DE. I doubt I'll ever 'run out of revs' in 5th gear there, but it's been very illuminating to get the real info. -Thanks!
Keith
I auto-cross in the 951S with the S2 R&P and it is indeed a great 'zoomer' in terms of acceleration. (-once the boost wakes up of course!
) but on the highway it is a little buzzy... almost down to 20MPH per thousand RPM.These questions came mainly out of curiosity, and I'd partly assumed, partly guessed and possibly partly misinformed myself that the S2 swap was for durability rather than 're-gearing'.
I should be taking it to Sebring again next year and doing some DE. I doubt I'll ever 'run out of revs' in 5th gear there, but it's been very illuminating to get the real info. -Thanks!
Keith
12-07-2007, 11:32 AM
#40
Rennlist Member
I have worked on S, S2, Turbo and Turbo S transmissions, but I have never opened up an N/A unit. So I dont know what the differences are in the design of the gear sets.
I do know that the 0.829 N/A 5th does not have the same part number as the S and Turbo .829 5th. But I dont know what the difference is. I have been told that the Turbo 5th gears can be installed in N/A transmissions. So I would assume that the N/A 5th (either the .829 or the .730) can be installed in a Turbo/S2 trans, but is it the same size/strength?
See if you can get a reply out of Kevin Gross, either in a PM or direct email (he replied/posted in a thread on the 944 forum the other day, related to putting an S2 trans in an N/A).
12-07-2007, 11:45 AM
#41
Rennlist Member
Great info, Jim!
I auto-cross in the 951S with the S2 R&P and it is indeed a great 'zoomer' in terms of acceleration. (-once the boost wakes up of course! ) but on the highway it is a little buzzy... almost down to 20MPH per thousand RPM.
These questions came mainly out of curiosity, and I'd partly assumed, partly guessed and possibly partly misinformed myself that the S2 swap was for durability rather than 're-gearing'.
I should be taking it to Sebring again next year and doing some DE. I doubt I'll ever 'run out of revs' in 5th gear there, but it's been very illuminating to get the real info. -Thanks!
Keith
I auto-cross in the 951S with the S2 R&P and it is indeed a great 'zoomer' in terms of acceleration. (-once the boost wakes up of course!
) but on the highway it is a little buzzy... almost down to 20MPH per thousand RPM.These questions came mainly out of curiosity, and I'd partly assumed, partly guessed and possibly partly misinformed myself that the S2 swap was for durability rather than 're-gearing'.
I should be taking it to Sebring again next year and doing some DE. I doubt I'll ever 'run out of revs' in 5th gear there, but it's been very illuminating to get the real info. -Thanks!
Keith
It really wakes the car up on the street. Easier/quicker to find the power band in every gear. Comes off the line better, etc. Car just "feels" faster.
There are very few tracks in the US where you would run out of gearing with the 829 Turbo 5th with the S2 R/P - unless you have big hp.
The banking at Daytona might be one of them. You can just about hit the rev-limiter in 5th between 1 and 2 at Brainerd International.
I love the S2 R/P at Road America. Makes driving the track easy and shifting is a no brainer. With the stock Turbo trans, there are 3 to 4 corners that dont feel right (either too high rpm in a lower gear, or too low rpm in a higher gear). But I dont like the S2 R/P at Brainerd. With the Turbo trans, the entire backside of the track is 3rd gear. With the S2 R/P, you need to hit 4th gear in 3 places. Those additional upshifts and downshifts, make for a lot more work and can slow down the laps times, more than the additional acceleration makes up for.
12-07-2007, 02:39 PM
#44
Instructor
Join Date: Dec 2002
Location: San Diego CA
Posts: 158
Likes: 0
Received 0 Likes
on
0 Posts
Thanks guys for the good information here. I just installed a complete S2 tranny in the racecar two races ago. Wow, what a nice difference. The car is much "quicker" and stays on boost much better. I used to get pulled big time coming out of corners vs the 911's. It's much closer now!
So, should I pull the S2 r/p and put it in the 951 box or just keep the S2 box complete like I have now? Keep in mind that fastest track we run is Ca Speedway where top speed on the front straight is about 155 (with the turbo box). I don't mind loosing a little top end at this particular track when I can make it up on the infield with the better S2 gearing.
Thanks again for the good info!
So, should I pull the S2 r/p and put it in the 951 box or just keep the S2 box complete like I have now? Keep in mind that fastest track we run is Ca Speedway where top speed on the front straight is about 155 (with the turbo box). I don't mind loosing a little top end at this particular track when I can make it up on the infield with the better S2 gearing.
Thanks again for the good info!
