Other Transaxles

Decided to kick this topic off because I know there are alot of knowledgeable and experienced people here that can come up with a stronger, better geared transaxle setup for the V8 944...
Here's what I've been working on so far (pissload of research as of now).....
Here's why I'm leaning towards the R154 as 1st choice.....GEARING RATIOS and huge/wide gearsets

Trans First Second Third Fourth Fifth

AX15 - 3.83 2.33 1.44 1.00 0.79
AR5 - 3.753 2.26 1.37 1.00 0.729
MA5 - 3.753 2.26 1.37 1.00 0.729 (Colorado/Canyon/Hummer H3)
MA5 - 3.75 2.26 1.51 1.00 0.729 (Solstice/Sky)
R150 - 3.83 2.062 1.436 1.00 0.838
R151 - 4.31 3.32 1.52 1.00 0.83
R154 - 3.25 1.95 1.30 1.00 0.75
R155 - 3.954 2.062 1.436 1.00 0.805
NV1500- 3.85 2.25 1.48 1.00 0.80
NV3550 - 4.01 2.32 1.40 1.00 0.78

The Jeep AX15 4x4 tailhousing will swap right onto the R154 transbox or the MA5 tranny from a GMC Canyon or Solstice/Sky which would be my 2nd choice and may just become 1st choice as I am reading these boxes have better synchros (triple cone?) than the R154 even, plus the MA5 is all over the place for $500-750 with low miles...

Looking at facts/dims....
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This is a Jeep T5 and a transfer case adapter and I photoshopped a Corvette C5 differential (3.15 R&P)to it and know that it would be @20" from the front face and the C5 axles hang below the shaft line by 3" just like the Audi box in the 944...
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The 1 thing I'm not sure of is if I do put the tranny face to torque tube right near the Torsion Tube, the axles will be level to the wheel hubs, but be set back by 4" (so essentially angled forward)...
And again all input and down right flaming as long as it it constructive, is certainly welcome....

Well, just my .02...

The only reason i would really consider a different transmission would be for the gearing, but honestly now that i've swapped the NA 5th and gone to a taller tire (285/35 18), the freeway rpms are pretty darn reasonable... Reasonable enough that i wouldn't bother going with a different transmission unless it were a bolt-in affair and didn't weigh any more (weight being a big concern...i don't want a tail-heavy car).

How much power are you planning to make?
As far as i'm concerned the Turbo box can handle whatever we throw at it for the most part... With a plate behind the pinion it sounds like it's as strong as anything we'll ever find. Start with a good box that already has a cooler and an LSD, put a plate behind the pinion, and maybe cryo treat it...i don't think you could ask for much more.

The axles are another weak spot, and then there's the fact that we can really only fit a 295 or maybe 305 tire in the back.

Don't let me stop you from experimenting...i'd love to see what you can come up with! It's just not something *I* would ever do....

""""The axles are another weak spot""""
Hence the C5 inner axles can be grafted onto the 944 outter axle halves..... Eric (Admin) says he's done something similar to the Viper rear end he's swapped. Another plus is the C5 differential will unbolt right on or off and Final Drive ratios changed easily. If you look at a Corvette LS1 gear ratios, they are even better than 944 Turbo transaxle ratios.

What does the Audi Box weigh?
the R154/MA5 weighs 115lbs wet and the C5 differential about 35-40lbs (150lbs)

My point with the axles was this: If we get a bulletproof transmission, we break the axles. If we get bulletproof axles (which we could also do for the 951 trans), then we still only have a 305 tire. With only a 305 tire, we'd need a lot of weight transfer...which i'm not willing to do to an autocross/road race car. At some point, you just go out and buy the Corvette!!

Sorry, i don't mean to be so pessimistic about it. I guess it's just not something i'm really interested in at this point. I'd love to watch though

How are you going to get these other transmissions to remote shift (especially the AX5/15)?

I think we should check out our 914 hybrid brothers on this matter. I think they use a flipped G50 transmission with great success?

the trannies have the same shift pattern as the 944. It wouldn't be difficult to make an adapter at the shift mech since the 944 shift rod goes straight back to it.
G50 manufacturer rhymes with ORSCHE

I seem to remember someone putting a 930 transaxle in a 944. I can't find the info though.

I would think that the easiest would be a 911 based transaxle, although a little pricey. G50's are plentiful enough and have the same spline as the 944 TT. (930 as well)

xschop wrote:The 1 thing I'm not sure of is if I do put the tranny face to torque tube right near the Torsion Tube, the axles will be level to the wheel hubs, but be set back by 4" (so essentially angled forward)...
And again all input and down right flaming as long as it it constructive, is certainly welcome....

A couple thoughts and questions:
The angled forward axle shafts doesn't sound too appealing... not enough real estate to move everything forward? Possible to shorten the TT?

Since you're considering/using the Vette diff, why not the Vette trans also? Too big, or?

Any chance you could edit/add to your OP to include the original application for ALL of the listed transmissions?

New guy to the site, but half shaft angles effect how a chassis reacts both on and off power, that includes forward and back as well as up and down. Moving the inboard attachment location by a few inches could make for a very interesting ride.

There are always ways around the problems the cars have. We know that in the end it is money and how much it takes. I am not opposed to any of the ideas that can be brought up and accomplished.

If some one has been able to offer a better solution to the transaxle issue with out destroying the weight balance the car has to offer, then be my guest and show us what you have.

The only way to figure if the parts will work, is to fit them. All the measuring in the world will never get you fully prepared for the final install. I know I am a CAD engineer.

I say either except the trans as the weak link in the car and drive it top end for that, or sell your setup and get a drag car.

cfgioja wrote:I say either except the trans as the weak link in the car and drive it top end for that, or sell your setup and get a drag car.

What an odd piece of "advice" considering the intent of this site and group you're talking to.

I like the 930 transaxle ratios and only 4 gears to choose from, it needs to be flipped I think for the 944, no Torsion tube cutting is a plus, but again a PORSCHE transaxle is ducketts and hell on the wallet if something breaks...
I found another alternative available. It is all wheel drive and can easily be converted to 2WD (unlike the Audi 4WD boxes)and doesn't need to be flipped (R&P)
I'm still not happy withthe ratios...would be a definite upgrade to the 944NA Ratios for sure...

Canada and U.S. WRX spec
Measurements: Gear Ratios (5MT)

First Gear 3.454
Second Gear 1.947
Third Gear 1.366
Fourth Gear 0.972
Fifth Gear 0.738

Reverse Gear 3.333
Final Drive Ratio 3.7

I am not sure why the 951 transmission gets the misconception of being so weak. I built my first 951 LT1 conversion in 1998, it made 360rwhp and I drove it for 5 years with no transmission failures(5R gear box). I have run the 968 6 speeds(gearing too tight for V8), AOR's,5R''s and 9U 5 speed gearboxes behind LS1 conversions, so I have pretty much tried all of the 951 Porsche gearboxes. I don't do drag race clutch drops or bang gears like in did in my old 69 Z28 but these cars are not drag cars and I am over all of that. I do use them for track days, street use and yes I frequently roll into the throttle and break um loose in 2nd. As far as gearing, go look at Tremec 5 speed transmission that are typically used behind V8's and you will be amazed how close the ratios are to a 951 transmission, especially if you do the NA 5th gear swap. If you want to go drag racing, buy an open diff box for $500.00, weld up the spiders and run it till it blows and then go buy another one. I say don't knock um until you have actually tried one for an while. My current car makes 450+rwhp and has been doing it on the same 5R transmission for 4 years now with no trouble.

heres 2 reasons why I'm diggin this tranny...
1) longitudinally split case makes life easier....

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2) aftermarket straight cut gears for drag racing or helical cut gears of all kinds of different ratios that won't kill the budget....

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Boxster transaxle in a 944.... all but two bolt holes match already. Shifts remotely with two cables. Price of the tranny is comparable with the 944 transaxles. Just throwing this in with the rest.

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Easy to convert to 2wd for the 9-fo-fo...
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And the benefit of the Subaru box is???

ghostcloak wrote:And the benefit of the Subaru box is???

Cheap parts and can put power down since some subie's can have upwards of 400hp.

Stupid question here ok I here the transaxle's on these car's , even the 951 turbo's are prone to well blowing up. I want to stick with the original transaxle and hear the 951 turbo with the 5th na is the shiznit as long as you don't keep dumping the clutch off the line.... my question is what about the 944S transaxle everytime I talk with someone on buying a 951 lsd and cooler and they find out I have a 944S their question is why would you want to swap it out for the turbo due to the fact that the 944S is geared almost the same as the 951 turbo with the na 5th gear swap.
So should I stick with my original 944S transaxle or should I find a lsd turbo and switch out the 5th gear?

Apparently the people you talk with drive Porsche's with puny motors . The S box has a 3.8ish diff just like the n/a, whereas the turbo is a 3.375 diff. It's the difference of taching 2000@60mph or 3000@60mph.

The S box is just like the turbo box but with the NA 3.88 final drive. You could put a 951 R&P in a S box but the R&P set up is very time consuming. The S and 951 have physically wider gears than the NA and fewer thicker teeth on the R&P due to the ratio difference 3.38 vs 3.88.

Best off the shelf Subie box looks to be the Forester one with the 3.7 R&P. The Subie box has all kinds of different gear ratios available aftermarket, but I can't find a better R&P ratio. If they came with 3.3ish ratios in some box, I would pull the trigger and get one because I wouldn't have to cut into the rear floor pan area in front of the torsion tube. The first set-up with the r154 and C5 differential does need the floor pan cut, but I get Corvette axles out of the deal and can be relatively easy to convert to 944 wheel axle flanges...
Another benefit to doing this set-up is the 944 TT can be shortened and made so that less TT bearings are needed and easy to change out/upgraded... I'm still pondering

The S ring and pinion is 3.875. (8:31) It is the same strength and dimensions (outside of tooth count) as the 951. It is completely interchangeable with the 951. Either can be retrofitted to the earlier transaxle but the ring gear area of the case needs some clearancing and 3rd gear needs an additional spacer. I know of an itallian guy that swapped an S r & P into his GT40 that he races.

Another thing that can be done to increase reliability is to cryo treat or shot peen the internals. The Turbo S had shot peened gears and shafts.

Question:
Wouldn't a transaxle, that splits its torque between R+P's, have smaller/weaker R+P's by design/cost savings? What is the tooth root width of the ring gear?
Most Subaru transaxles that I have seen used in 2WD configs have been in very light cars, <2200#, with less than 300hp.....have we found any examples of 3000=# cars with 400+hp running these transaxles?

Regarding "S" R+P; I would think that if the ratio is bigger and the overall diameter of the R+P is the same as the 951 then the teeth will be narrower....and thus weaker, if made from the same material.???

I agree with V8CGTS; shot peening and cryo treaments can help a gears life.....

I am still not convinced that an stock Subaru trans will work well in a high HP 2WD app.

Theoreticaly, the S-S3 gears would be weaker because the cross section between each tooth is thinner. But there are other areas of the transaxle that will break first making it a moot point.