CPTdooberhead

Andrew,
sell your car and get a 968.....turbo it. It already has the 6 speed gearbox
-Randy

JPR

"Regarding the 968 tranny - I'm not a big fan of 6 speeds, and based on the difficulties involved in making it work for your 951, I'd stay away."

I accept that you may not be a fan, but what are the difficulties that everyone refer to? I did it the swap and involves no more dificutly that removing and reinstalling the stock tranny. Now the cost of getting it done may persuade you to stay away but not installation.

Jpr

AL951

you are right JPR!!!..............I really don't think is that difficult.

sweanders

It would be great if you can list the parts needed.

Porschefile

From what I understand, I thought all you needed for the 6spd to bolt up is the 968 axles (different lengths I think), and possibly a mount. I can't remember who I spoke to, but they performed the swap themselves and that's what I was told. As far as the speedo, that seems to be the only tricky thing.

Laust Pedersen

It would be interesting to know what the difference in transmission loss between the 5-speed and 6-speed is. With more gear wheels in the box the 6-speed must have more loss, but how much?

Up-shifting at 6000 rpm in the 5-speed gearbox will give an rpm drop to 3500, 4100, 4400, 4800 rpm from 2nd to 5th gear respectively. Since the typical power curve on our 951’s is quite flat from 4000 to 6000 rpm, only the first shift could benefit slightly from a closer ratio.

On a car with a flat torque curve (peaky power curve) more gears make more sense, heck, I believe that ZF now has developed a 7-speed box.

Laust

sweanders

True in straight line acceleration but on the track the bigger gain with more gears o tchoose from is to fin one that lasts all the way through a bend so you don't have to ride the rev limiter until it straightens.

NZ951

So the general thought is the S2 box, shorter gearing and bigger crown and pinion. I cant find any info on the speedo fix for the 6 speed. The boxes are the same price.

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.

fast951

951 Torque tube works fine with the 968 6-spd..

tems needed for the conversion:
- 6-spd transaxle
- Left half shaft
- shift linkage/rod (front to back)
- shifter (inside car)

Of course you will need to figure out how to get your Speedometer to work...

JPR

The 6th speed in the 968 tranny is not any taller that the 5th in the 951 one. If anything, it is slightly shorter. The gear spacing is very thight, it is hard to find yourself needing an inbetween gear in any situation.

Jpr

M758

I know that Chris Cervelli ran 6spd gearbox in his 450+ whp 3.0L 951 GT1 racer car.

He purposfully installed the thing. I think he did it for strength and commonallty G50 gearbox parts. In any even he felt it was an upgrade of a 951 S gearbox even without an external oil cooler.

I remember this as we talked about it once. Unfortunalty that was few years ago I don't remember all the details as to why.

Tomas L

I hope I ain't starting a HP vs TQ debate now... But you have to calculate HP drop for each shift. Even if the TQ curve is flat, the HP will drop due to the drop in rpm.

Tomas

Laust Pedersen

Tomas, I don’t think we disagree about the physics, but my assumption was as stated: “Since the typical power curve on our 951’s is quite flat from 4000 to 6000 rpm … ”, which obviously means, that the torque curve drops proportionally with rpm.
I also stand by this statement: “On a car with a flat torque curve (peaky power curve) more gears make more sense”

Laust

CPTdooberhead

The 968 speedometer signal comes off of one of the front wheel abs sensors, I believe most people use a pickup attached to one of the (968) axles with a hall sender, then you send that signal to an electronic ratio adapter (ERA), and then onto the speedometer. If you don't have ABS, you're going to have to try another route. Maybe you could just install the ABS spindle's and hubs- that way there would be a SPOT for the ABS sensor- so just take the abs sensor output and send it to the ERA and on to the speedometer.... you can make it work
-Randy