Diff ratios

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Sidney'61
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Diff ratios

Post by Sidney'61 »

Hi,
I have a standard 1098 diff (4.22?) with my 1275 minor at the moment, what would be the benefits of 3.7 or 3.9 diffs etc..?
How would they be expected to change accelleration, top speed and fuel consumption? so of course which diff would give me the best of all 3?

Not that I'll be doing any work on the car for a while, just stuff to bear in mind... :roll:
Andy W____________1961 2-door 948cc (Sidney)_____________1963 2-door 1275cc (Emily)_______

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bmcecosse
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Post by bmcecosse »

3.7 is ideal for just about everything - with a modifid 1098 or 1275 engine. It will do 50 in second, 80 in third - and ...... in 4th! Best for mpg obviously - only snag - it struggles on really steep hills - but how often do you go up a REALLY steep hill ? Fit a 3.9 if you wish - but you will regret not getting the 3.7! So happens there is also a handy Mini speedo (1248 tpm) that matches perfectly!
Last edited by bmcecosse on Fri Sep 18, 2009 12:03 am, edited 1 time in total.
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MColes
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Post by MColes »

Be no good for me around here. I have a 4.22 and that can struggle getting up the hills here. I usually have to stick to third, doing about 30 and I get there eventually :roll: :lol:
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PSL184
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Post by PSL184 »

Don't bother changing Andy - You run a 5 speed box (if I remember) and it will make 5th gear pretty useless....
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charlie_morris_minor
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Post by charlie_morris_minor »

from a different post..

all calcs are based on 145/R14 tyres

if you run a 1098 gearbox with a 4.22 dif 60 - 65 equates to around 3750 - 4000 rpm in fourth

if you run a 1098 gearbox with a 3.7 dif 60 - 65 equates to 3250 - 3500 rpm in fourth or 3750 - 4000 gives you 70 - 75

if you run a ford 5 speed with a 4.22 dif 60 - 65 equates to 3000 - 3250 rpm in fifth or 3750 - 4000 gives you 75 - 80

for the sake of completeness a 5 speed with a 3.7 dif 60 - 65 equates to 2650 - 2900 rpm in fifth or 3750 - 4000 gives you 85 - 90
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