I have a bit of a dilemma. My car is a Merkur XR4Ti with the factory 2.3 turbo engine, but with an XR4x4 drivetrain. Needless to say the sump is custom. Anyway, the car is setup with the 2.9V6 front differential, which I have to assume is a 6.5" differential with a 3.62:1 gear ratio.

Now, I have two rear differentials to use with it. Currently installed is a regular XR4x4 7" rear diff with a 3.62:1 gear ratio. However, I have an XR4Ti 7.5" rear diff with a Quaife installed in it - and a 3.64:1 gear ratio.

Running the 3.62 6.5" front diff with the 3.64 7.5" rear diff may be possible without destroying the center diff's viscous coupling, but I'm not sure.

Reviewing the Quaife catalog, it appears that a 7.5" front differential was installed on Cosworth XR4x4s (and probably the Escorts, too). This leaves me with two questions:

1.) What is the gear ratio for the 7.5" front differential?

2.) Is is true that all V6 4x4s (Sierra & Escort) have 6.5" front diffs, and all Cosworth 4x4s (Sierra & Escort) have 7.5" front diffs? I suspect it's not this simple.