Swapping Differential ??

[George Zeck]

Hi All -

I haven't been on here all season due to the purchase of a boat. I just found out that MG2012 is ~ 30 miles from some close relatives. Thinking of how to make the car a bit more easy to drive for 12+ hours.

When I had the engine rebuilt (Eric Jones, RIP) he also 'upgraded' the diff. Don't know what ratio I have, but I do know there are 3 basic ones. Car originally was a 1964 (63?). One diff is wonderful and racers fight over it (not mine). One is stock (boat anchor) and presumably was my old one. The middle one was the "upgrade".

My issue is with the upgraded one - at 65MPH; I'm pulling 4000 RPM (and speedo is off by 6 - 7 MPH; previously reasonably exact). Would the "boat anchor" one reduce the RPM's? I'm OK with giving up a bit of accelleration in favor of better top end (faster & or quieter would be prefered).

Thanks for your help.

George

1964
AH Sprite MKII

 

[drooartz]

Stock for your car was a 4.22. You've probably got a 3.90 in there now if it was changed. The 3.90 lowers the RPM for a given speed. There is a 3.70 around as well that would drop them a bit more, but at the cost of acceleration. They came in the last of the rubber bumper cars and are a bit hard to find.

Only real way to substantially drop the RPM at speed any more (assuming you do have the 3.90) is to put in a 5-speed.

 

[George Zeck]

Thanks Drew.

 

[nomad]

George: The ratio is marked on the diff housing at approx 10 O-clock as you are looking from the drive shaft back. With a mirror, flashlight, and putty knife you can probably find it. Sometimes on the edge of the flange sometimes facing front. Stamped in with a dye stamp.
Agree that you need either a 3.7 from 77 78, I believe, or a 5 speed. Theres always 2 lanes and a relaxed drive however!!

Kurt.