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MG Midget and Sprite Technical - diff upgrade.

i really wish my car had overdrive but its too much messing about and like to keep as original as possible. is putting a 3.9 or even 3.7 diff in a noticeable upgrade on mk2 1098cc. i put a 3.9 in a 1500 midget once when the 3.7 was noisy and didn't notice anything.
thanks bob.
bob taylor

Yours would originally be 4.2 so going up to 3.9 is about an 8% increase in mph/1000 rpm. Going to 3.7 (from 4.2) is a 13.5% increase, getting on for double. For a standard 1098 3.9 would probably be fine. Going to 3.7 would probably be a bit too much unless it's tuned for more torque rather than bhp.

A 1500 is quite torquey and very capable of making the most of a 3.7.

I have a 1275 developing about 80bhp in a Frogeye with a 3.7 and it's ok for everything except town driving because 30mph is a bit too low on the torque curve for it so I'm constantly changing 3rd/4th.

I had a 3.9 in it and it was more pleasant around town but the 3.9 was a bit noisy when it got hot, whereas the 3.7 is silent, so that's what I'm sticking to.
Rob aka MG Moneypit

This thread was discussed on 29/06/2016

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