6 Speed Box

[George Elliott]

I would appreciate any comments on the success, or suitability of a 968 manual box in a 951.

Also, what parts are required

thanks in advance
George
944t

 

[nick_968]

Very short ratios for the turbo engine. Some like it, some do not. Most only upgrade for a 3.0 engine but even then it has questionable benefit unless it is a track only car. I find the ratios a little too short to load up the turbo properly in the lower gears and a title too short for a comfortable cruising rpm on the motorway. I think you need the 968 driveshafts.

 

[Neil Haughey]

Isn't it a lot heavier as well?

 

[944 man]

Aftermarket diffs are easier to find as theyre shared with 911s. City driving will be easier too. 968 transaxles are now extremely expensive for what they are.

 

[zcacogp]

ORIGINAL: Neil Haughey
Isn't it a lot heavier as well?

... and also had a pinion bearing that was made of cheese?


Oli.

 

[Lowtimer]

I've thought about this a lot and did a lot of numerical analysis a few years ago. When I first got my car I felt the gaps between ratios were a bit on the wide side. especially in terms of the boost threshold and where the car really delivered the power. However, in practical terms I found it was vastly easier to improve that situation by fattening up the effective rev range of the engine than by tinkering about with the gear ratios. With a dual port wastegate and a suitable chip set bringing the engine well on song by about 2800 rpm I don't really find myself wanting six ratios any more

Of course it all depends what you want to do with the car. If you drive exclusively in the UK and therefore don't have the opportunity to cruise for long periods at very high speeds then it does not really constrain your enjoyment of a tweaked 944 Turbo that it runs into the rev limiter at about 164 mph in top. And a setup that spools nicely from significantly below 3000 rpm makes the the standard gearing is ideal on the motorway as 70 mph puts you well within the rev range where putting your foot down makes things happen quickly.

But if you were doing a lot of high speed work in Germany, or for some other reason wanted to raise the top speed significantly, then having done the sums, I found that in theory what you'd really want on a tuned Turbo is the 968's six gear ratios combined with the final drive ratio off a Tiptronic. I don't have the exact numbers to hand but it worked out something like this: If you had something like a 340-350 hp big capacity turbo running relatively modest boost that would give you about 175 mph at the power peak, with 6th gear being a workable wafting gear at 70 mph and starting to pull hard from about 90 mph upwards. And the other five ratios would largely reproduce what you have now.

While it was a fun experiment on paper, for what it would cost to do in the real world, I decided there are probably far better ways to spend the money.

 

[colin944]

I have often thought about fitting a 986 box to my S2. However I just cannot justify the high prices that are being asked for them. Not worth the money as far as I can see.

 

[944 man]

Theyre now twice as worn out and four times the price.

 

[MarkK]

968 box is way more fragile,944Turbo gearbox is way stronger and long lasting,

 

[944Turbo]

For a higher top speed/longer 5th the V8 convertors put a na 5th gear into the turbo box, If I recall correctly this gives you around 199 mph at 6,700 rpm not sure how far down in the rev range it drops you changing into 5th from the top of 4th though.
Tony

 

[zcacogp]

199mph? That'll be a theoretical top speed, I'm guessing.


Oli.

 

[George Elliott]

What a great forum,
you lads have been thinking outside the box...[8|].....excellent ideas there which I had never considered.
never considered some of the ideas and was unaware the 968 box was poor, its a Getrag isn't it?

the reason I asked is I sometimes go to grab sixth.....

many thanks
George
944t

 

[TTM]

I run a 3.0 turbo and as a regular user of derestricted Autobahns I noticed early that a tall top gear was needed. In fact I barely take the car out anymore these days, unless I have a mate to visit over in Germany.

The easier way to build a tall ratio 968 gearbox is to source gearsets from some FWD Audi/VW diesel gearboxes, as the 968 gearbox belongs to the same family of the 01E gearbox series. I will leave you the fun of hours browsing through ETKA (VAG/Audi's PET equivalent) to see what can be made to work.
The bottom line is that only gearsets 3/4/5/6 can be swapped, as 1st and 2nd gear are part of the main & secondary shafts, and we can't use the ring & pinion from the Audi gearbox as the differential is larger (or smaller, can't remember which was which when I measured them). The cherry on the cake is that there are several 'boxes to choose from, which will offer different gearings. I chose one that has given about the same first 5 gears of the 944T 'box, but with a super tall 6th on top. Makes for cruising at 120mph at 4k rpm, which is über cool when you have the kind power to properly propel the thing.

I keep hearing about fragile synchro rings on these gearboxes, and some Audi folks in the US seem to offer carbon-layered upgrades, but I have no idea if it's worth the cost over new standard synchro rings, at least for people like me who run their car only on the road and change gears like if they were walking on eggs after doing such a pricey investment (talking roughly €5k after all is done, including sourcing a used Audi gearbox on ebay for €500 with thankfully undamaged gearsets, a shiny new OS Giken LSD, rebuilding half shafts with unmarked cages, plus all the parts needed to fit this all to a 944).

 

[George Elliott]

TTM, thanks for that,

I see two options with 6 speeds, one is close ratio (6 within the existing 5 spread of ratio's) or two is "overdrive" (an additional 30mph/1000rpm top ratio like you describe). It is this that would cancel my tendency to go for 6th as the car just pulls 5th so easily.

I appreciate the steer on the 01E info.

Cant sign off without asking.......what will she do on the 'bahn [8D]

George
944t

 

[333pg333]

My .02c worth. I've run standard 951 5 speed, 5 speed with S2 r&p and a 968 6 speed. My preference is the 5 speed with the S2 r&p and I would think unless you're an Autobahn Stormer like Thom, this version is a great mod for most of us. I am not entirely sure if the "˜issues' I have with the 6 speed are unique to mine or a common issue but I find when wanting to shift from 6th or 5th straight into 3rd that it just gets vague and wants to go back to 5th. Of course I'm heel/toeing and never had this issue when going from 5th into 3rd on the 5 speed. My builder who doesn't have a lot of experience with Porsches feels that the detents on the 6 speed are too ineffective. He doesn't seem to have the same issues as me when shifting but he just lets it happen by finding it's own path before moving back into 3rd where I'm used to my old 5 speed where you could be very fast between the gears. We stuck with the stock gearing on the 6 speed and it is quite similar to the 5 speed with the shorter ring and pinion. There seems to be varying opinion on gearing with turbo motors and in the end I didn't want to buy an expensive set of aftermarket gears without being sure of this. I don't find this gearing too short but haven't driven this on the street. If I hadn't sunk a small fortune in the 6 speed box (mods, plumbing, lsd, billet side plate, LR axles) I'd be inclined to go back to the 5 speed. The only thing is that we'd have to remove the shorter ring and pinion I believe due to too much speed down the main straight. The short answer to this question is that I'd stick with the 5 speed (and seriously contemplate the S2 r&p) and put the rest of the money you'd spend doing the conversion on something else. []

 

[TTM]

Patrick, interested about what you mean exactly with the "detent" thing.
What I have noticed is when a gear is not fully engaged on the 968 gearbox, the shifter will not go back to neutral position by itself with as much conviction as on the 944 gearbox. I think this is caused, well at least partly, by the "spring plugs" located at different spots on the gearcases and that provide the actual resistance felt when changing gears.

I believe a side result of this is that it is difficult to make a short shift mechanism for the 968 gearbox, because reducing the leverage on the shifter control rod out of the 'box means a need for sufficiently high reciprocal torque for the angular movement of the output control rod, and that torque is, I think, partly supplied by the "spring plugs". Some weeks ago I tried to adapt a 944 SSK to my 968 gearbox and when the gears were engaged there was just not enough counter force from the 'box to help disengaging gears with minimal effort - Disengaging was actually as hard as engaging, both a lot harder than with the standard 968 mechanism.

Apart from this I have not noticed the lack of precision you mention, pretty much regardless which gear is targeted. Are you sure you have everything tight at the back? (pun unintended...)

 

[944Turbo]

ORIGINAL: zcacogp

199mph? That'll be a theoretical top speed, I'm guessing.


Oli.

I seem to remember Dfastest on rennlist pushing very close with a modded turbo lump. not sure if anyone actually has done it with official recording, though there was talk of him attending speed week out in the dessert somewhere. I think if I was making the effort I would be tempted to go for a higher rev limit and 200

 

[Diver944]

ORIGINAL: 944Turbo


I think if I was making the effort I would be tempted to go for a higher rev limit and 200

Where is Ben when we need him []

 

[JamesO]

ORIGINAL: 944Turbo

ORIGINAL: zcacogp

199mph? That'll be a theoretical top speed, I'm guessing.


Oli.

there was talk of him attending speed week out in the dessert somewhere. I think if I was making the effort I would be tempted to go for a higher rev limit and 200

Some kind of cake race?

I'm still running mine with the S2 transaxle, I have the turbo box that needs a new oil pump drive gear and output bearings plus the bits of oil pump drive gear removed.
A taller 5th would be nice for cruising (although I do love the third gear like acceleration in 5th), I may have to dig the spanners out for the first time in ages. Setting the shims up for the bearings and lazyness has stopped me Is there an easy way to do it?

 

[TTM]

I searched quite a bit on how to possibly adjust the R&P clearance on a budget but kept coming back to the conclusion it's not possible to do it really properly without the painfully expensive VW special tool. But then I suppose some intelligent people have found ways to do without it, as it's not like there aren't quite a few of these transaxles running around.