differential ratios... race rover build

[John Boy]

Hi all, quick question.. The 1963 IIa I am working on has the 4.7 -1 differential ratio, the 1995 Discovery I am stripping has the 3.54 - 1 differential ratio. If I use the 63 IIa differential with the 1995 3.9 GEM and the ZF auto transmission, How will my tach read at 65 mph? I'm guessing higher, but how much higher than if I use the 3.54 - 1 diff?
Cheers
Johnny B

[punkinracer]

The tachometer is triggered from the altinator so the gearing will not make a difference to its reading. Speedo on the other hand will read totally wrong, if you are able to even hook it up. Later ones had a trigger module rather than a traditional speedo cable.
Pat

[red90]

4.7/3.54*29/32=1.20. 20% higher engine speed versus the stock Discovery. The transfer case still has a place for the speedo cable drive.

If you are really racing the axles with break very quickly and you would need to drop a few grand into upgrades.

[John Boy]

Thanks brothers, you confirmed what I suspected. Cheers