I have the 1100s block with a 2.9 diff too and it is great at cruising speed. The supercharger means it doesn't lack grunt, though no doubt I have sacrificed some acceleration with that diff. But i wanted overall best fit for performance rather than 0-100 time.

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Build thread for Supercharged 1275 1967 Deluxe Resto
Build thread for Mini ute conversion 998cc Turbo

sounds like 2.9 is the go.

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Zulu...

1967 mini Cooper S

Depends what you want. If you don't do much freeway work, a 3.44 is great. Steams up big hills in 4th gear.
Me, I run a 3.64 in mine. It goes well with the RE282 cam for suburban running. But it might get the 3.44 put back in next year.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

I mainly do 10 - 15 km runs in traffic on the flat...

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Zulu...

1967 mini Cooper S

A 3.1 diff with Mini K gears (22G1128 box) will give you Cooper S gear ratios in 1-2-3, and a taller 4th. Best of both worlds.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

Kev, I haven't checked the numbers but I think the cooper S has taller 1. 2. & 3 gears to a mini K box. So a standard mini K with a 2.95 diff would make up the difference between a Cooper S with a 3.11 and then have an even taller 4th for cruising.

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Find a job you love and you will never have to go to work !

According to http://guess-works.com/Tech/ratio.htm
Cooper S Close Ratio 4 synchro 3.44:1
@4000rpm
1st gear = 20mph
2nd gear = 32mph
3rd gear = 49mph
4th gear = 66mph
60mph in 4th gear = 3630rpm

Standard ratio 4 synchro 3.1:1
@4000rpm
1st gear = 21mph
2nd gear = 33mph
3rd gear = 51mph
4th gear = 73mph
60mph in 4th gear = 3230rpm

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Cooper S sold here were all using a 3.44. Mini K had a 3.647. Yes the S indirect gears are taller, by 1/17.
a 3.1 diff makes Mini K 1-2 and 3 gears same as an S with a 3.44, because you are running an 18T pinion not 17, and still have a 62T crownwheel. Is equivalent to going from 17T to the 18T on the S box 1st motion shaft.

a 2.95 diff makes 1-2 and 3 even taller than a stock S.

Note that a 3.1, 2.95 etc CW/P would need to be imported, the tallest ratio we got was 3.44. In Cooper S, and most rodchange boxes.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

Kev, this brochure has K listed as 3.76 ?
viewtopic.php?f=32&t=94542

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"Would you run a road 1275 with a 3.76, it would be geared like an 850.
OK for a track car or a streetbound racer."

Hmmm?

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The bitterness of poor quality (or Crappy Workmanship) remains LONG AFTER the Sweet Taste of Low Price is forgotten.

Only early K was 3.76. most were 3.64, as were 1098 Clubby with remote box.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

I thought 2.9 would only fit the a+ rod change box??

You just need to bore the bearing retainer out to clear the pinion.
Same as for a 3.1.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

This is how I put a 2.95 in a 22G1128
viewtopic.php?f=2&t=90443

Phil

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Find a job you love and you will never have to go to work !

Ah,nice one!
Thanks.