1966 Mini Cooper S, 4 speed Syncro/ 3.1 Final Drive ?

[jl46]

Hello All,

I have a 1966 Mini Cooper S Mk1 1275.
I am thinking of changing my original gear box with 3.44 final drive
for a new box with 4 speed syncro and 3.1 final drive.

I am looking for a quieter ride ,lower revs at highway speeds (interstate-65+ mph).
I would appreciate your thoughts on this change.
Thanks,
Jim

[Nick W]

I have recently changed from a 3.44-1 to 3.1....first gear is not so instant now ,but fine for road use ,its now much quieter on the motorway in 4th at 60 mph .but it did slow me down off the bends at blyton!.

[ianh1968]

<SNIP>for a new box with 4 speed syncro and 3.1 final drive.
I am looking for a quieter ride ,lower revs at highway speeds (interstate-65+ mph).

Can you be more specific on which gear-set you are thinking of?
Or have you not chosen yet?

I could list at least 6 fairly common clusters that will go in a 4 synchro box.
Are you looking at helical/straight - Pre 'A+' or 'A+'.

The example below is:
3 Synchro Cooper Ratios
- 10" Rims Yoko A008 - 3.444
vs.
4 Synchro Pre A+ Standard Ratios
- 10" Rims Yoko A008 - 3.105

TOP TIP: Click on the image and your browser may blow it up bigger and clearer!

3COOP-vs-4STD.png

These examples were generated by this tool found here for calculating gear/diff ratios...
http://mk1-performance-conversions.co.u ... anical.htm

The gears are spaced a bit further apart, but first gear ends up being
almost exactly the same as before.

If you use the "S/GT" set, first becomes 5.4mph/1000RPM

If you use the "Wide Ratio" box, the one with the 4.004 first gear
along with a 3.105, this will give 4.5mph which will be lower than
the original Cooper first gear on a 3.444.

If you are looking at proper close ratio gears, cam choice is a factor
that needs to be considered with a higher diff.

Ian

[carbon]

3.1 final drive with the standard helical S gearset works well for a road car in my experience.

I am running this combination with 1293 using MD266 cam. Still plenty quick enough off the line, with a 3.44 or 3.65 I think spinning the wheels would become more of an issue as I am using 145x10 tyres...

[carbon]

The other benefit of changing from 3.44 to 3.1 diff is that the speedo now reads pretty much spot-on...

[Andrew1967]

I run a 3.1 diff in my 1330cc but otherwise standard S engined car (with an S ratio 4 synchro box) and I have to say it is fast enough off the line and pulls well in the other gears. Would love to get it rolling roaded sometime to get the best from it.

Cannot compare it to a similar car with a lower diff but its certainly pretty civilised at 60mph.

[Nick W]

drove the senic route this morning in the riverlin vally , 3000 rpm = 55mph in 4th ,4 syncro s/c c/r 3.1-1 , my speedo is also very accurate ,checked against a sat nav .not sure I have the correct speedo fitted though ,number is sn4417 18a 1280, which I think is correct for its original 344-1 diff ,but yellow gear change points seem optimistic ,1st-34mph 2-55mph 3-78mph.my engine is a 1380 A series twin h4s gas flowed head =90bhp?,maybe its from a 970s?.
also I recon you could go to 29-1 for cruising if you have the power

[1071 S]

Me too.... I have a warmed over 1330 and really like my 3.1. Years ago (when i was more closely involved) I found the 3.1 quite good on our local hill climb. Maybe it blunted the edge in certain places you picked up time by allowing you to hang onto lower gears longer - rather than waste time with an upshift.

On the road I often really wish there was an extra gear... 4k at 70+ mph is fine but a 2.9 would probably be better...

Cheers, Ian

[smithyrc30]

also I recon you could go to 29-1 for cruising if you have the power

Definitely. I had a 1400cc unit fitted with a 544 cam, worked head with 1.5 rockers and a 2.9:1 diff. It went ok. Running 165/70/10 Dunlops it was just under 3000rpm at 60mph

[ianh1968]

I'd add to this that my MiniMarcos is currently 1330cc...

It has a 544/643 cam, 1.468"/1.218" valves (37.3mm/30.9mm), 11:1 CR,
1.5 rockers, LCB etc

I am running the 'S'/GT set with a 3.105 diff on 10" rims with A008 Yoko's
First is 5.4mph, top is 18.0mph (using 1076 wheel revs per mile).

From what everyone is writing here, a 3.1 is certainly realistic.

Ian