Trans questions

madweazl · 10-18-2004, 07:56 PM

Hello,
I'm in the process of building a long travel dune buggy right now and want to use a Porsche gearbox. It looks like the 930 will be the best bet for the application and I was hoping you guys could help me out with the differences between the various trannies.

From what I remember the 930s were available from '79-86 and there were numerous engine combos that sat behind them. Are there also differences inside the gearbox, for instance, did the turbo models have a stronger ring/pinion and gear stacks than the non turbos or just a stronger PP/clutch?

Trans will be mated to a V8 with a Kennedy adapter (more than likey a Northstar or small block aluminum Ford, not sure yet).

Typical ring and pinion ratios are 4.11 and 4.86 for sand use. I've read there are a lot of gearing options available so I'm going to assume a 4.11 is possible to obtain (or something close). What are the ratios for 1st-4th?

If you have any info you feel would be helpful please let me know as I know nothing about these transaxles

klaucke · 10-18-2004, 08:05 PM

The 930 will definately be stronger than a 915 box which similar era 911's used. I think the 930's mostly had stronger sychros and gears, not sure about the ring and pinion. My Porsche has very high gearing in all gears (4th and 5th both are overdrive) which is made up with a lower ring and pinion, I think mine is 4.60 something... so I think you'll find a ring and pinion in your range, but realize the whole tranny is geared higher than an american counterpart. Different year 930 boxes had different length bell housings too, I think, so be aware when you get your adapter and clutch.

Also, is this a Baja bug dune buggy or a sand rail? There could definately be some mounting issues were it a Baja bug.

I see companies that advertise 930 boxes for sale for use in high hp dune buggies in the magazine Hot VW's, so you may want to pick up a copy and speak with one of them.

Depending on the hp/tq your plan to make, and where you plan to drive, you could possibly get by with a 5 speed 915 box too.

madweazl · 10-18-2004, 08:38 PM

Sorry for the lack of details [bonk]

The Northstars stripped down and tuned for offroad applications usually make about 370hp/tq and the Ford will make about 330hp and 350lb' of torque. I'll more than likely go forced induction after the first season (work out all the kinks in the computer first) and max will probably 500hp/tq.

Length of the trans isnt a big issue as its going in to a tube chassis rear engine "sand rail" (see pic). Car will primarily be used in the sand with some occasional trips to the desert.

The 4.60 R&P would work just fine but the gearstacks will probably need some work which isnt a big issue (these trannies are a lot cheaper and stronger than the purpose built units we typically use). Was your trans regeared or did they come from the factory with 2 overdrives? The lower its geared the better for my application as I only need a top speed of around 110-120 (more than I'll use I imagine).

The car pictured isnt mine but is the same model and manufacturer (our cars has a lot more tubing for strength/safety). Weight will be around 2100lbs, rear tires are Extreme 14.50 (width) and are 33 inches tall so that will effect the final gearing as well.