Are there lower ratio differentials?
 

Anyone know if there are lower ratio 'matched' differentials that can be installed in an E53?

Lower than the 3.64 off the 4.4? Isn't that what you have now Bryan?

Yes, lower than 4.4. Ratio of the 4.6 is 3.91

4.44

RealOEM.com * BMW E70 X5 3.0si DIFFERENTIAL-DRIVE/OUTPUT

RealOEM.com * BMW E70 X5 3.0si Final drive (front axle), parts, 4-wheel

Are you saying the the 3.0 diff is a plug and play in the 4.6 and has a 4.44 ratio and has the same strength gears as the 4.6?

I'm saying Performance Gearing or KMS or VAC can make it so. The guts should be interchangeable but contact any one or all of them. Can't see why the metallurgy would be different. 4.44's would be perfect IF we had a second overdrive gear.

I have heard of good things about diffsonline.com. They specialize in BMW gearing.

Sent all suggestions a text. diffsonline responded that he will get back to me on Monday but he thinks he can build a set at 4.44.