MPD47

Bass, I'll try and snap some more photos for you this week.

944CS

Because the individual gear ratios are similar between an S2 and a 951 trans you'll want to choose a gearbox with the highest final drive ratio that can still handle the power. This will give you faster boost reponse and less turbocharger "lag". I would absolutely go with an S2 gearbox before I chose a 951 box. Your car will be faster with the S2 box. 968 box would be an even better choice. Even better still is 968 box with custom gears.

bitburgerluvr

Given the car is 924, I would look into the G31. This will help you avoid many torque tube, etc modifications or swap. Also, the stiffer gears will help the acceleration and gear choices are almost limitless and cheaper. Remember, this is what the original 924 racing cars were using. However, the synchros are not the best from what I am reading. I never drove a car with a G31 installed so I cant say just how bad they really are.

I like the G50 too but I think youll need modification for this. I wonder if the standard G50 is much stronger than the Turbo S transmission? Some say the 968 box isnt as strong as the S2.

chrenan

Steve's car is a 924 in the loosest sense of the word. A picture of his current engine build and old 924 race platform are below. I'm guessing modifications and engineering beyond stock are not a major concern...

Bass GT3

The G31 is not atn option sadly. Although the chassis is a 924, there is little left in reality. The G31 requires the 924 steel torsion beam as this is what supports the box. Secondly,as you say, the synchro's are a nightmare, and pretty much unobtainable. Also, they cannot handle being downshifted at speed, which is a major facor in hillclimbing. It seems rolling shifts from 2nd to 1st destroy them, and 3rd to 2nd isn't much better.
It would only work if someone was making dog engagement gears, but i think the cost of design and manufacture would be prohibitive. So it sems the 944/968 family is the choice.
As an aside, following some research i have carried out, it sems Audi fitted the 968 box to some of their cars, including he hotter versions. it seems that tougher 1st & 2nd gears are available, as well as better synchro's. I would then have the entire gearset and R+P shotpeened, to aid strength. Not cheap, but better than manufacturing a complete box.

Steve

bitburgerluvr

First, that car looks awesome!!!! Youre right, it wont be cheap but should work alot nicer than the G31. I didnt know that the downshifting was a problem with the G31. So, I'll forget all about that transaxle.

So why not the G50?

Bass GT3

G50?? Is that the 968 box? If so, that is the route i shall be taking. Even stock, the ratio's look ideal, as they seem to have a roughly 25mph spacing with my tyres.
As Chrenan said, engineering the ridiculous seems to be my specialty
The car above was effectively my development mule. Work has started on her replacement. She shall be a non sunroofed, GTR bodied car, with all that i have learnt from the orange car. This includes dry sump tank placement, fuel tank placement ect, and all the associated routings. The suspension is late 944 with JRZ coilovers all round. The rear torsion bars are removed, and the new shell will be fully seam welded and gusseted, especially the rear shock mounts. Weight is planned to be sub 2000lbs, with around 380 bhp in sprint trim with the larger turbo. Hill trim will be about 300bhp with the smaller turbo. ECU & electronics is Pectel SQ6 including WRC spec anti lag and 9 way traction control. tyres will be 14" & 11" crossply slicks, with a custom 2.6:1 steering rack and electric power steering. Guard transmission LSD in the box ect.

Steve

bitburgerluvr

The G50 is the 911 transmission. They flip the differential and do other modifications to adapt to the 924/944/968 series cars. I like the idea of using the 930 transmission. It is only a 4 spd but they are absolutely bullet proof.

Let us know what you decide.

DanR

I have a 951 s box with a S2 ring and pinion and it does pull well out of the bends due to lower gearing. Only issue (if you call it that) is that due to the lower gearing some corners are spend in a higher gear whilst everyone else is in a cog lower! Depends on the track and corner as to whether it is better or worse.

chrenan

So is the G44 transmission in the 968 a G50 transmission that has been adapted to transaxle use? Any relation to the G50?

Oddjob

944S r/p is not strong enough for a higher hp application - it will fail. Can either put an S2 r/p in a turbo (or Turbo S) trans, or put a Turbo 5th gear in an S2 gear box - basically end up with the same thing. Oil cooler is nice depending on how hard/long the car is to be tracked.

FYI, the S2 box has the same hardened input shaft as an AOR (Turbo S) trans - so the same hardened teeth on 1st and 2nd gear. Turbo r/p is beefier and likely quite a bit stronger than even the S2 r/p - although the S2 r/p has proven to withstand high hp applications. All other loaded components between a Turbo and S2 gearbox are same (other than 5th gear ratios - which never fail; and the non-Turbo S 1st and 2nd gear teeth on the input shaft).

968 trans is slightly heavier than the 944 units. Price out the Guard LSDs for a 944 vs the 968 trans - the 968 LSDs used to be $3-500 more. 968 trans will be a lot more $$ and a little harder to find than an S2 gearbox, or a turbo trans and buying an S2 R/P to install (still available from Porsche new).

Lemming

I have run both a 951 and S2 transmission in my Frankencar (924S with 968 engine). Even running small diameter wheels (15's), I much prefer the s2 transmission. Eventually I will replace 5th gear as it is a bit too long.

I thought about dropping in a 968 transmission but decided against it; I really don't want to be shifting that much.

Good looking car you have there

333pg333

As another with the 951 box and the S2 cw&p swap, I would say that this could suit your application very well. Currently I have a pretty much stock 2.5L engine with a stage 5 turbo and this combo should be a complete LAG machine but it's fine because of the S2 cwp. This is a temp engine however most thought it would be terrible and it's not, especially for the track so this might be your easiest option.

Bass GT3

Guy's,

Thanks very much for all the input, itrs very much appreciated. As i have a 968 box sitting in my garage, cost is not an issue thankfully I also have a 944 S box that i guess i could fit the S2/Turbo internals into.
Although the 968 box has tighter ratio's vs the S2 or turbo box, i suspect this may suit the character of my engine. Remember that this is the VW based 2 litre engine, not the 2.5 porsche lump. It is happiest kept between 4k & 7.5k rpm. Secondly, on the hills, tigher ratios are benficial in keeping the motor spinning in it's sweet spot, especially when you are hauling out of a moderatly slow corner. Yes, the additional weight is an issue, but this may be a small price to pay. And having this weight hanging over the rear axle won't hurt as the rear of the car is where the majority of the weight is removed from in the first place. Thirdly, apart from the higher 1st gear, the 968 ratio spread is very similar to the 924S box, which has served me very well on the hills as i rarely even use 4th, but on the sprints, the 5th gear was useless.
Finally, as i use 25" diameter slicks, i will be limiting the boost in the lower 2 gears primarily to avoid excessive wheelspin, which makes the traction control's job harder, but the added bonus of this is that it will protect the box from being overloaded. The typical limit will be 7psi in 1st and 11-12psi in 2nd. I have been using 21.5" slicks, as can be seen in the above picture, and these would light up in a heartbeat due to the hand grenade nature of the power delivery!!( 70-230 ft/lbs in 300 rpm!!) The car above is running a stock 924S box, which was fine at my previous class limit of 250bhp + slicks, but the 5th gear was ridiculous due to the huge ratio spread.And the typical duration of a race is less than 90 seconds, so there is scant chance of over heating the box!! However, i shall be fitting a temp sensor into the new box, so i can tell whats happening in there. If necessary, i can fit an external oil pump triggered by the ECU at a given temp, which can scavenge the oil from the box, pump it through a cooler and return it to the box.
Once again, many thanks for all your thoughts and input. I really appreciate getting to hear what experiences you guy's have.
And if you are wondering what has been made or moved in the engine bay, here is a little pic prior to going off to the engine dyno for running in. In fact, this config has changed slightly as she is now running an additional set of injectors up by the plenum. These seemed to make a healthy increase in the top end power over the lower set



Steve

lee101315

Are you attempting to set a land speed record? The gears on the 930 boxed are long and spaced wiiiiiiiiiiiiiiiiiiiiiidddddddddddddeeeeeeeeeeeeeeeeeeeeee...
think driving 55mph in 3rd gear