Hi, i just did Targa in a mini which i built as a 64 Cooper S, 1310 engine which ran a standard 4 syncro gear set. i used a 3.7/1open diff. 1275 torque worked ok with std ratios, final drive was ideal, run to 8000rpm. But i think as Dr mini said a 3.9/1 would be good in a small-er bore. I just would think twice about running LSD, a real hand full in tarmac rallys. I did rally Tas also and run open diff aswell, wheel spin wasnt a big issue.
Currently building a 998 Cooper for next year, may use 3.9/1 or 4.1/1final drive.
Mini sport mini, sccr box, open diff, 3.7/1. Happy mini-ing.

Hi, i just did Targa in a mini which i built as a 64 Cooper S, 1310 engine which ran a standard 4 syncro gear set. i used a 3.7/1open diff. 1275 torque worked ok with std ratios, final drive was ideal, run to 8000rpm. But i think as Dr mini said a 3.9/1 would be good in a small-er bore. I just would think twice about running LSD, a real hand full in tarmac rallys. I did rally Tas also and run open diff aswell, wheel spin wasnt a big issue.
Currently building a 998 Cooper for next year, may use 3.9/1 or 4.1/1final drive.
Mini sport mini, sccr box, open diff, 3.7/1. Happy mini-ing.

G'day Bricknut, The only classic Mini that I remember competing against in this year's Rally Tasmania was Graeme Robinson / Bruce Robinson in a 1978 Leyland Mini Clubman S. I believe it was running a KAD 5-speed box which had selector problems and put them out of the event after Day One.
Which car was yours?
As for diffs, I agree with MiniMan, it would be advantageous to use an LSD and a 3.7 ratio would be my choice as well, but how easy they are to drive depends a lot on the type of LSD and how tight it's set up. I run a Quaife in my Cooper 'S' and am quite used to it's characteristics, and although it's set up quite soft it can still catch you out by 'tram-lining' if you aren't concentrating.

For what it's worth, standard diff in a 1071S was a 3.76:1.
I've not rallied Tassie, but have driven our ~90HP 1293 (with 3.65 diff) around it- I'd say a 1071 would want a 3.76, or maybe a 3.9.

I've hill climbed with a 3.76 on an 1100 and it was barely acceptable. 2nd gear was too low and 3rd was too high. Options, go to say a 4.1 and pull 3rd gear, or goto a 3.4 and have enough in 2nd gear that I don't have to change. Every time you change gears you loose 1 second. Based on this, am I better with a higher ratio diff that'll give me more speed range in each gear, or do I want to be cog swapping all the time on something lower?

Sounds like you need a close ratio gearbox!
Safety concerns have led to high speed sections being reduced on tarmac rally stages through the use of chicanes, but it's still easy enough to reach 160+ just not sustain it for any length of time.
Another point to consider is your comfort and sanity during the transport stages which can be quite lengthy. The last thing you want is to sit at 5000rpm on the highway speed limit between special stages.