Hi

I was discussing with my neighbour about Mini gear boxes and he has a close rato gear box and intends on putting a 3.1 diff into it.

I am sure a read some where this is not a good idea as it makes first to second to short

can any help me answer this question correctly

Ta

Kiwiinwgtn

to make it relative, what the engine and it's spec?

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good point

1330 cc with a 286 cam a plus engine and box

depends on ur driving reqs, it will run sweet on the hwy

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A good friend will come and bail you out of jail...but a true friend will be sitting next to you saying "Damn...that was fun!"

what about changing up and down thru the gears will you lose / gain anything..

Please define "close ratio"
I have just fitted a 3:1 diff in my project which is designed for a supercharger but not yet fitted. The gearbox is a late clubman type so not sure of ratios but I have found that once the car is moving it is great and it seems to have dropped the revs in top gear by around 800, so cruises at 100kph at around 3500rpm
The only issue currently is starting on very steep hills but nothing a few Extra revs won't solve. And eventually the supercharger should solve this issue. The change between each gear including 1 to 2 seems ok
Hence my original question
Maybe one of the technical gurus will have a better explanation?

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1969 Cooper "S"
1967 Mini Deluxe
1973 Clubman Van (the fleet spare)
1978 ex 1275 LS ("Wizard" Eaton Supercharged)
2015 HSV GenF GTS(occasional drive & tow car)
2019 MINI F55 Cooper S

It is a factory close ratio helical gear set A+

it uses a different lay gear and first motion shaft from standard

Kiwiinwgtn

Same as Cooper S MKII. I have a few of the same - unobtainuim - sets.

IMO, the diff would be too tall, but I like them nippy off the line. I ran a 3.2 with a similar spec engine for a while. Great on the longer trips and definitely livable around town, but hard pushed getting better than 15 000 KM from a clutch.

Just a little too slow off the line for my liking. I have found - after also trying a 3.6, a 3.44 is about the best for it.

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Thanks GT

you answered my question it effects the off the line speed

Ta

Kiwiinwgtn

No worries.

If you look closely at the cars that these Tall diffs were fitted to, most, if not all, had 'twin line' gear sets. These were the oposite of the close ratio sets, ie, 1st gear in a Cooper S set is 3.2:1, the Twin Line sets are 4:1 ('standard' sets being 3.54;1). They used these wider sets to 'make up' for the tall diffs.

And these were in stock engines with tame cams. Big cams and tall diffs don't mix on a 4 speed gearbox.

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