diff upgrade

[a8pte]

please can anyone tell me whats the difference between a 3.7 diff upgrade and a 3.9 diff i want to change mine thanks (or which is the best to put in)

[charlie_morris_minor]

it depends on your engine and the type of driving you do..

i have a 3.7 in my convertible with a 1098 engine that is ok not the best but by no means the worst engine and i find it a terrible combination as i drive around town mainly so i have to rev the car hard to get anywhere / accelerate and i do not take advantage of the lowered revs at top speed..

with a healthy 1098 / 1275 you would not need to rev the car as hard and you will have the advantage of lowered rpm when cruising on the motorway.. so horses for courses

[a8pte]

charlie m m i have a 1275 midget in my morris

[charlie_morris_minor]

so a 3.7 would be ideal

it will drop your revs at cruising speed and you should not see any issues with acceleration around town.

[a8pte]

charlie m m got a chance of a 3.9 any info please

[plastic_orange]

3.9 is standard fitment in a 1275 midget.
Overall gearing is also dependant on wheel/tyre combo.

Pete

[charlie_morris_minor]

sorry i misunderstood your question.. i did not understand you were asking which was best..

if you do most of your driving around town and like to accelerate as quickly as possible I would look to go with a 3.9

if you spend most of your time on the motorway and therefore dropping the revs for the same speed I would look to go with a 3.7 dif

4000 rpm with 145/14 tyres and a 3.9 dif gives you just under 74mph
4000 rpm with 145/14 tyres and a 3.7 dif gives you just under 77mph
assuming you are in 4th and the gear ratio 1:1 which the moggy boxes are. of course you would never do more than 70 but you get the idea.

just for the purpose of comparison a 4.2 gives you just over 67mph

needless to say over and underflating your tyres will have a dramatic affect on these and the values and i think the cost / availability of the two difs is more likely to drive my decision..

[a8pte]

charlie morris minor sent pm

[a8pte]

still urgently looking for a 3.7 diff anyone got one please

[a8pte]

charlie-morris-minor sent pm

[bmcecosse]

I run a 3.7 final drive (not 'diff' - it remains standard) with a slightly uprated 1098 engine -and it's fine! But to be honest - the difference between a 3.7 and a 3.9 is hardly significant - and the 3.9 seems to be a lot more affordable these days!