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For reference: The ring gears are the same diameter to fit in the same trans case. So the more teeth, the smaller the teeth have to be to fit that diameter. The Turbo R/P has 8 teeth on the pinion, 27 on the ring gear. S2 has 8/31. These are pictured below, Turbo ring gear sitting on top of an S2 ring gear. The S has 9 teeth on the pinion, 35 on the ring gear. The teeth are proportionally smaller yet than the S2 gear set, and therefore inherently weaker.
And be aware that the S r/p in a higher torque application is a known problem, documented years ago. Some comments from a 2005 thread:
"This has been common knowledge in porsche/performance/technical circles for years. There are articles/letters from Bruce Anderson and others in Panorama tech sections dating back to OCT 89 on the subject, stating that there had been known failures of the 944S 3.889 R/P when used in a 944 Turbo (in under 10k miles), and that Porsche openly stated that the S R/P was not a strong as the Turbo and should not be used in that application."
"The car that I am aware of (this was 12 plus years ago) was a standard turbo (non-Turbo S) with Authority Stage II chips, so approx 270 bhp, and was a dual use street/track car. Failed around 10k miles and broke the teeth off the pinion, ring gear survived. I do not know anyone that has installed an S ring and pinion in a Turbo in the last decade."
One of the posters in that thread, that was using an S r/p in a turbo, posted back within 8 months that the pinion gear broke.
Certainly use will have a big impact on longevity. Hard launches vs loafing to the grocery store. But I suspect track use is on the harder side of the spectrum. Go ahead and try it, see if you like the gearing. But be aware of the risk. I would not plan to leave it in too long, and in the meantime, start looking at building up an S2 r/p box (as time and funds become available) for the long term.
Well it's not a track car exclusively, and I only run 225 tires all around, which with RE71Rs is enough for now. I never dump the clutch, but I do drive it hard after it's off the line, and shift as quickly as I can in spirited scenarios. And there is the potential for rapid autocross starts. My only worry about the AGR is the R and P failing, which some sources say is inevitable in a turbo, but other people I trust say it's fine.
I could just wait, find S2 R and P, install that with an OS Giken and have the 5P rebuilt, which would probably be the strongest and best option, but it's also near 5k to do, vs installing the AGR and filling it with swepco, which is obviously significantly cheaper.
Probably cheaper to find a S2 trans (AOS) and install an aftermarket LSD unit, or finding a good condition AOT outright. The cost of an S2 R/P and then getting an LSD to install in a Turbo trans will be the most expensive route. If you are just running DE's, I don't think the trans cooler is necessary.
I just finished building a S2 transaxle with new OS Giken Superlock LSD for a customer who has a 320whp dedicated track 951. I can easily add an oil cooling systems to any transmission as well.
I broke my 5r back in 2003 on the freeway with only 355rwhp 2nd gear downshift
Porsche must have also thought there was a weak point on the 1st and 2nd gears on the input shaft, which is why the input shaft gears were strengthened on the AOR/AOS/AOT transmissions.
But for perspective - the 5R was intended for a car with about 190-200 rwhp, the AOR for a car with about 210-220. On a good day, the Turbo Cups were making maybe 250-260 rwhp. The 944S trans AGP/AGR was designed only for about 160 rwhp.
So with this many of us on RL and elsewhere pushing these north of 300/400/500(rare I'm sure) whp, do you just expect to go through transmissions? Would a franken trans based off 5P with OS Giken, S2 R&P, and hardened input shaft from AOR be enough to take daily abuse from a 325whp motor? How do you time attack guys making north of 6 do it?
So with this many of us on RL and elsewhere pushing these north of 300/400/500(rare I'm sure) whp, do you just expect to go through transmissions? Would a franken trans based off 5P with OS Giken, S2 R&P, and hardened input shaft from AOR be enough to take daily abuse from a 325whp motor? How do you time attack guys making north of 6 do it?
Tony Garcia's secret was not to use 2nd gear on the track, you can ask him, but I remember he mentioned his secret in a thread here on rennlist
I agree. I never have to use 2nd gear on the race tracks I run in the Mid-Atlantic area. My car is no more than 235whp and I have been using an AOT transaxle with oil cooler system. Oil cooling plays a big role in the transmission performance and durability. Tony G has been running a very efficient oil cooling system on all of his transmissions. Also, he has been keeping them in excellent condition in terms of bearings, pinion depth and correct backlash by having the transmissions inspected on a regular basis. I currently have his last AOR transaxle (it is in close to rebuilt condition) that he ran before moving to the current Albins sequential trans.
There are some things that still could be done to improve the performance and durability of the Turbo transaxles for higher torque and horsepower applications. I use modern widely available metallurgy technologies to treat the input shaft and lower gears for all of the transmissions I built for V8 conversions.
Bit off topic but how would a 968 box work and hold up in a turbo application?
Could that be a good option? Availible with LSD but not cooler. Gearing should be good but dont know about strenght.
Firstly, I would agree with Oddjob. He is well versed in these Transmissions clearly.
Secondly. Re the whole load vs ratio thing that Sid mentions...I have asked this question many times and been given different answers/opinions. My take is that the load thing might be more important to Drag Racing than Road Racing. Certainly being more in the accessible range of the turbo helps in acceleration despite the seemingly extra gearchanges a short final drive seems to bring. That may be more of an illusion as your ratios don't change, just the final drive. However, as mentioned there are enough of us that have used the S2 r&p with success to virtually use as a 'control' in comparisons. Look to Youtube video under JET951 or 333pg333 for some in car showing the 951/S2'd gearbox in action.
Thirdly. Most of the guys with really high hp don't dump the clutch. They either know better or don't require this with their racecars. Time Attack cars being case in point. Flying starts rather than a gridded takeoff.
Fourthly. The 968 gearbox works fine in terms of holding the high power levels. We have proved that and so have others. The ratios aren't so dissimilar to an S2 or 951/S2 box but you have the extra gear. To date, we haven't even used 6th gear on our car in earnest. Obviously it's also dependent on where your motor 'wants' to change up to the next gear. If it's an 8v the general rpm change point is going to be below 7000rpm. More likely low 6's. So you might get to use 6th cog in those circumstances if the straights are long. For us we've only changed gear between 7000-8000rpm so we can hold 5th for longer. All horses for courses sort of stuff.
For DE probably try and find an S2 box and a cheap LSD would be sufficient. Especially with less than 400whp.
I have used S2 gearbox with self-upgraded LSD for 3 years, have made many drag race starts too. 400+whp, 2.5 16v turbo. Worth noting that my 924 weighs 1240 kg's with half tank of gas.
I have used S2 gearbox with self-upgraded LSD for 3 years, have made many drag race starts too. 400+whp, 2.5 16v turbo. Worth noting that my 924 weighs 1240 kg's with half tank of gas.
That's peep my friends and he knows what he is talking about it
I've posted extensively on this in the past. It's not a black-and-white situation, but here's what I recommend you consider.
The 944S and 944S2 ring and pinions have an almost identical ratio. Because the S2 pinion is stronger, it's the way to go. Its strength is pretty much on par with the 944 Turbo r&p.
If you are swapping r&p sets in a car making high horsepower, don't even bother unless you plan to set them up correctly with the factory toolset esp the VW385 kit. Pinion depth is critical to longevity for a hypoid pinion, as these cars have.
Also critical to longevity is the general mechanical condition of the rest of the transmission and its lubricant. The bearings must be in good condition and must be set up correctly, as must the ring-to-pinion free play (backlash).
There were a lot of people swapping 944S r&p sets into 944 Turbos late eighties. They pretty much all broke, but not for the reason you think. While the 944S is less mechanically robust than the S2, the real reason I believe they all broke is that shops doing the swap did not set 'em up. The S has a unique Ro (nominal pinion depth) that is different from all the other 944 series gearboxes, worth noting.
To give you an idea, here are a couple of pictures. Unfortunately I did not have a S2 pinion on hand when I took these, but it's close to the 951.
You can get undersized pinions to survive if you set them up correctly and maintain the gearboxes. I have a bunch of clients racing 944 normals with the 4.11 r&p and even smaller, mostly in SCCA and other non-Porsche series.
Use of the AOR input shaft is also a good idea because of the hardening Getrag did to the 1st and 2nd gear teeth cast into it. It's a simple and easy upgrade to an earlier transmission, takes 3 - 4 hours of labor. I have for some years seen a lot of 944 series transmissions coming in for service that have significant erosion of the 2nd and occasionally 1st gear teeth at their root on the input shaft, even the 944 normals. Need to keep an eye on that.
The type 01E transmission in a 968 is a fine unit and I've probably rebuilt more of them than anyone out there. That said, no one has ever convinced me that it's in fact "stronger" overall by some standard. Certainly the bearings are a bit bigger and would be expected to survive a bit more loading. A few negatives to consider. First is the different design of the gear operating assemblies: if you hammer an 01E's dog teeth, you can peen them over and find yourself with a transmission that won't go into a particular gear no matter how carefully you shift. The 944 series doesn't have this issue. Second is the question of six versus five gears, which on some tracks will mean more shifting. Last, they are more expensive to service and the parts have become quite difficult to source from Porsche, and VW/Audi isn't carrying them anymore, last I checked. (I keep a full inventory on the shelf because of the lead times. Fun fact: because of a US versus Germany trade grievance having to do with frozen chickens back during the Johnson era, bearings cannot be expedited (PDX'ed) from Germany to the US. I am not making this up...)
Thanks for the great post Kevin. The shop (Buchanan Automotive) that we have had do the S2 r&p conversion are well versed in these transmissions. Here's a useful thread they put together for reference. https://rennlist.com/forums/944-turb...age-heavy.html
In terms of the 968 trans, I have never liked it as much as my old 951 w/ S2 rp for smoothness and alacrity of gearchanges but I thought perhaps it was just an issue with my particular transmission and possibly the indents. However in terms of holding power it has provided no problems up to 550whp on the dyno and a bit less on the track. What I'd really like to have found is some straight cut gears for this transmission. Unlike the Audi version of the 01E box where there are some options available, there is nothing as far as I could find.
07-04-2017, 11:45 AM
