I have a 740 turbo with a 3.73 rear end. I am interested in a 3.91 rear as a performance upgrade. I have located a 1987 Volvo 760 with the 6 cylindar engine. The salvage yard tells me this is a 3.91. Can any one tell me if the 760 6 cyl came with the 3.91? Is there a way to tell from a serial number or ID marking? What other models came with this rear axle? Thanks for the help.

The speedo sender changed in about 88 or 89. Compatibility might be as easy to ascertain as checking the wire connectors, but I am not sure.

Bear in mind that turbos make boost faster when loaded up. You will be raising rpm to gain performance and will decrease the load on the turbo. Still, most people seem to agree that the lower ratio will help. Volvo used the 3.91 on the 240 Turbos with automatics. The improvement that you would probably like even more is either a higher stall speed torque converter from MVP (about $300 plus 4 hours installation) or a used smaller turbo and later manifold assembly (as little as $300 used plus 4 hours installation). Either would dramatically improve off the line acceleration on your automatic 740T. Both would not be critical, since the small turbo would make boost within your stock stall speed. Either of these would be more desirable to me than the rear swap. If I ultimately wanted much more than 200 hp, I probably would not go for the small turbo swap.

Philip Bradley

Basically, you have to head for the junkyard with a razor and clean off the whole area of the axle tubes beside the diff. There is a small sticker which, in my experiance, is covered in crud and undercoating. It will say the ratio.

Best of luck,

Rene

The label is on the left(driver side) axle tube.