I've done some research on this since I use the 968 Box in my V8 Conversion. I too have the desire to lenghten the rations for 5th and 6th for highway cruising. No need to spin the 'cubes to get a car this light going with the V8 torque. So Heres' the skinny:

The 968 box is a variant of the Audi 01E widely used with their S cars. The main difference is Audi uses the wider 1 gear and because of these they have a bump on the gear case to house it. Other than that, and the bellhousing for the transaxel mount, they are basically the same. There are a host of gear rations available but it is believed that only 5th and 6th are interchangeable but this would work since the stock '68 6th is a .778 and Audi has all the way up to a .5something (they use this on their diesel variation).

This is actually was porsche itself did for the 968 turbo. The rations they used for 5th and 6th were picked from the Audi bins (I think they used the same ratios as on the late 90's Audi S6), and they also paired this with a 3.40 final drive to get 30.3mph per 1krpms in 6th. I don't know were the 3.40 r/p came from but, since the 5th and 6th gear are available, I think that picking the right gear from Audi's selection would achieve the same end result for highway cruising.

Most of the information can be seen here:

http://www.elektro.com/~audi/01E/

If you look closely they have a link for a discussion of the 968 box.

Hope this clears up things,

Jpr

 

JPR, great info. Anyone else know about or have experience with this?

 

DFASTEST,

Its definantly the truth. Audi guys have been using our short gears and diffs in their audi's. In fact, if you look at the tranny there is no Porsche stamp, but an Audi VW casting. I have just never found a source or a need for a source for different gears. Maybe you can be the first to take this task on.

Wes

 

ever consider a diff from guards?

 

Considered it, but have since gone with another solution via aftermarket. Something a little more robust and quite a bit cheaper than comparative Guard diffs. Guard diffs are very nice units, but the cost detered me.

Wes

 

Seriously guys you should do more research on the diffs shown on page one of this post by JET951. These come out of a factory that makes diffs for Ferrari amongst others. They also make Quaiffes and I think a torsen type. Just because it comes out of Australia doesn't mean it's not worth checking out. These have been proven in our cars. JET951 has won the overall Porsche club championships for the State of N.S.W. with one. Not that this means anything to you guys but a great accomplishment up against the GT3's, 997's, worked Boxter S's etc...Definitely worth checking out. I'm putting one in my car soon with the S2 cw & p.

 

Now you guys got my attention! If the 6speed trans uses the R&P from a G50, the rest is even better!

JPR, what V-8 swap are you using this trans for??

 

Hey Bob,
What's the setup in your avatar? Looks interesting???

 

It looks to me like a GN (Grand National), or T-Type engine in a 951.


Rogue

 

Yes it is a Buick turbo V-6. TE63e turbo good for 690 HP. I currently only do 360 at the wheels but shut it down on the dyno at 4500 RPM. It makes 560ft lbs for torque.

Dafastest,

If you spend most of the time on the street go with the 40/40. IF you are going to spend more time at the track go for the 80/20.

 

isn't it difficult to get a hold of one of these 6 spd trannys?

 

If the following 5th and 6th gears were swapped into the 968 box what would be the theoretical top speed? This is assuming we stay with the standard 968 ring and pinion.

Original 968 5th - 0.912
New Audi 5th (RS4) - 0.81
New Audi 5th (RS2) - 0.86

Original 968 6th - 0.778
New Audi 6th (RS4) - 0.68
New Audi 6th (RS2) - 0.71

 

With a 255/40/17 (RD = 25.03) @ 6500rpm you'd have:

Original 968 5th - 0.912 = 139mph
New Audi 5th (RS4) - 0.81 = 157mph
New Audi 5th (RS2) - 0.86 = 148mph

Original 968 6th - 0.778 = ~163mph
New Audi 6th (RS4) - 0.68 = 187mph
New Audi 6th (RS2) - 0.71 = 179mph

But remember, the stock 4th is 114mph, so 148mph 5th would be ok, but 157mph would be leaving a bit of a hole. Going from 148 to 187 would be a tiny bit of a jump, but still be acceptable. The RS4 5th would leave quite a hole b/t 4th & 5th, but would be throwing 6th on top pretty close. The special 3.22FD would be the deal, but I'm not sure it's happening- you could throw a .86 on to that & get a much taller:
(.81)- 184mph
(.86)- 174mph
(.71)- 210mph
(.68)- 219mph

The stock gears w/25.03"RD & 6500rpm redline w/3.22FD are:
47mph
75mph
104mph
135mph
164mph
192mph

So, if you threw the stock 5th & 6th out & replaced w/the Audi (.86) & (.71), you'd get 135 in 4th, 174 in 5th, & 210 in 6th- you'd have nicely spaced gearing w/a tall top end, capable of breaking 200 before redline w/just the slightest hole b/t 4th & 5th. It's a few things to get to work together though, that all hinge on each other...

 

Joe, you should have enough info by now? So why not just get the 6sp so you can bang thru the gears and call it a day!

 

Thanks Robby, that was pretty much what I worked out as well but I wasnt sure on the calculations. I dont think the 3.22 is going to be an option for me so it will be the RS2 5th and a toss up between the 6th gear choice. To hit those 220mph figures with the 3.22 you would need some serious hp probably 600+ and the car probably doesnt handle too well above 180 so its all academic past that point for me. I am more interested in being able to hold 150 - 160 at reasonable revs and also being able to get there fairly quickly.