2QuickS

I have a 1980 931 snailshell that I intend to install into my 1988 944S. The CV flange on the snailshell has a 6 x 86mm bolt pattern.

Is there a CV joint with this pattern that will accept the 944S axle?

If not then is it possible to swap out the inner races to get the spline interface right assuming ball diameters are the same of course.

Gage

The torque tube will have to be changed to the 931 version as well to accommodate the different mounting pattern of the transaxle. I don't know if the engine side of the 931 torque tube mates to the 944 engine. Transaxle mounting will also be different. Seems like a long run for a short slide;-)

2QuickS

I have torque tube & will mount transaxle using cross member of the 944 and will create mounts as needed, I will not mount to torsion bar tube I can adapt to the bellhousing and clutch without much trauma. CV joint hookup is the unknown I seek resolution to now.

tempest411

Why use that transmission as opposed to the countless others you know will work without improvising?

V2Rocket

You need to measure the OD of the CV flange not the bolt circle. I suspect yours are 90 or 100mm OD...have you tried test fitting a 944 axle to the trans flange ?

2QuickS

Thank you Spencer!

Pilot diameter of snailshell flange is 100mm and OD of flange is 105.5mm. I have not checked fit-up of 944 CV or axle, I have the 931 tube, box & shift linkage assembled & sitting on the shop floor and am thinking ahead. My current project is my main focus which is completion of side draft carbs of my own design & fabrication; snailshell installation will follow my current project.

As to why a snailshell?:

• I prefer a dogleg gearbox (38 years with a 67 911S)
• linkage is much more direct with the snailshell
• It was designed by Porsche for use in the 924 chassis and is basically a 915 box arranged like the transaxles used on the 908/3 with gear cluster ahead of the final drive.
• Gearbox in the 944 is that from front wheel drive Audi, a "cost effective" alternative to the Porsche box
• 944 (Audi) transaxle has mass located behind read axle whereas the 931 (Porsche) transaxle has mass ahead of rear axle, good for reduction of polar mass moment of inertia.
• 931 box is much lighter than the Audi box

tempest411

I wasn't aware of those advantages. It begs to ask the question then, if the transmission was developed, why was it not used in at least the more premium variants, like the turbo (with upgrades to handle the increased power)? By discontinuing it's use, they've essentially thrown away the money they sank into developing it. And with these being Porsches and not Toyotas, why did they care about saving a few dollars in this way?

J1NX3D

I've always loved how compact they were. This is my previous '80 924 Turbo

J1NX3D

interesting question. Parts availability and cost must come into it somewhere. Maybe the snailshells were stealing too much from the 911 parts bin. They used it in all the Carrera GT cars up to the GTR, can't remember what the GTP had. They starting switching the 924 to the audi box in about '79-'80 and the turbo for the series 2 in '81 (US only IIRC)

V2Rocket

It was a racing-derived transmission, but it must've been very expensive to build that trans for 1 trim level of 1 model (931). Whereas the Audi trans that made its way into the 944 was already related to the 4spd trans in the 924NA, so they could have cost savings putting that same Audi trans type in the later 931.

In the late 70s/early 80s Porsche was a very small, niche sports car company that was perpetually cash-strapped. They didn't start making big bucks as we know them now until the Boxster and then Cayenne came out.

KevinGross

The 016 series transmission used in the 924S/944 series and much of the 924 series is a more modern and robust transmission design. A big difference is its use of Borg Warner design synchro rings, where Porsche had used their own balk ring design synchro in the earlier 356, 911, 924, and 928 transmissions. (Porsche has since moved on, largely, to a newer three-piece synchro design, as you see for example in the 996 series and the six-speed Boxster and Cayman transmissions.)

The type 915 transmission is not one I consider "racing derived" for the simple reason is that it's too difficult to swap gear sets, among other things. If you look at a Hewland gearbox design, or a 930 four-speed, they are distinguished by serviceable stacks on the two shafts once you pop the case section off. The 915 design (and its use in the G31 and VA/VB snailshells for the 924) is comparatively difficult to service and, thanks to its shift fork design, to get right.

Dan Jacobs

I worked at a dealer when that trans was under warranty
We sold a bunch of 931's
I think the reason they stop using them was that they sucked
They broke constantly. Of course that's just my real world experience

2QuickS

I assume Porsche wanted to keep the 944 an "entry level" Porsche vs. the 911 so cost reduction was the driving force. Also, the dogleg pattern probably was a poor choice for "entry level" drivers who managed to mangle the box due to the unique pattern

When I mentioned the 908/3 it was to highlight the similarity of concept of transaxle layout, not to suggest the 931 box was "racing derived".

Jay Wellwood

Not to mention the fact that Porsche partnered with Toyota about that time which resulted in transfer of Porsche IP to Toyota in return for Toyota advice on improving mass production techniques. Up until the Boxter/996 - Porsche labor for building these cars was astronomical compared to other competitors in the market. Introducing mass production techniques (i.e., eliminating the hand built production used up until then) drastically improved production times and throughout capability => increased profits. Currently, Porsche enjoys the highest profit margin within the VW/Audi auto empire of vehicles.

V2Rocket

There's whole libraries written about the "Toyota way" of production.
I work in the commercial furniture business and my main MFR uses the Toyota system for efficiency/QC. Crazy

Re: profitability...my brother worked deep inside VW for several years. Fun fact, a typical 991 only costs VWAG about 30% more to build per unit than a typical Golf. Now compare MSRP with that in mind...