GT5 Diff ratio

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Originally posted by yong num heng:
Hi everybody, I going Twin Turbo to my GT5 because is not easy to source American V8 parts in Malaysia if we want to go extra power. I will replace the Forged Piston for 8.5.1 C.R. and trying to choose the Cam to suite. I really appreciate anyone know the Final Drive Ratio for this ZF. Thank you

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I believe the ZF -2 final drive is 4.22

There are two possibilities for your later Pantera Gt-5. First, does your transaxle differential case have a flat curved top that smoothly curves up to join the bellhousing, or is the diff case more cylindrical with small ribs? If its the former, you have a late model ZF, better known as the 'M-1' gearbox and virtually notjhing interchanges with the early unit. On the late box, the gears are heavier, the shafts thicker and the cases reinforced. The ratios are also different.
Second comment: there is a ZF Owners manual available that should be required to do more than change the gear lube in these expensive, complex transaxles. All the U.S vendors and Pantera Clubs sell them very reasonably. Finally, there are different ring & pinione ratios available as well as different 5th gear pairs, and only those sold by RBT Transmission are 'real' ZF parts. Long ago, the ZF factory in Germany sold the rights to the name, the internal specifications and all the tooling to RBT in Southern California. Other mfgrs gears may or may not hold up especially under the extra power yopu plan to build. To my knowlege, RBT only sells the gears if THEY personally install them, since its easy to screw up in this trans, especially with non-stock parts.

Hi Yong.
Looking up in the Pantera Gold Portfolio 1970-'89 book by Brooklands Books, all the GT5's listed run the higher (Numerically lower) 3.77 crown wheel & pinion. - The earlier cars before the GT5 ran 4.22. I prefer the 4.22, since I personally dont get a chance to do alot of top-end speed and prefer the stronger acceleration the 4.22 offers.
The GT5 ratios are: 1st 2.23,2nd 1.47,3rd 1.04,4th. 0.85,5th. 0.71 which with the 3.77 C&P plus standard 345/35 P7's gave 148mph @ 6250rpm.
Going turbo is indeed an exciting option, but very ambitious & complicated. Especially twin turbo. Back in the 80's I was involved in a twin turbo build on a GT5 and it was a nightmare and very, very expensive. Especially since I live in a place like yours where parts avaiability and competent techn.knowledge is limited. In the Henry Rasmussen book on De tomaso's "Panteras for the Road" there is a 6 page article & excellent pics. on a twin-turbo setup which you must see. This book is out of print I belive, but is obtainable thru the various Pantera vendors. Think carefuly about going turbo. Are u competing in any events where u need the power? U would have to upgrade EVERY thing.Forced Induction generates so much heat which is already a problem. KIS: Keep it simple,- I always feel.Let us know how it goes and good luck.