3.7 DIFF

Post by **aupickup** » Fri Apr 04, 2008 10:44 pm

is a 3.7 diff ok for a 1098 moggie

Post by **IaininTenbury** » Fri Apr 04, 2008 11:42 pm

In my pinion, I'd say its a bit too high geared. I had one in my old 1275cc Midget powered van, and it made for very nice fast cruising, though round town was constant gear changing, rarely seeing top. I'd guess a 1098 would struggle a bit more with it.
If you've got one, pop it in a try it. I eventually went back to the 4.22 with the van as I liked the acceleration more than the cruising.
I didn't have a 3.9 at the time, otherwise I'd have used that which I guess would be a good compromise and may be as high as you'd want with a 1098.
Daresay someone will have a different experience or view!

Post by **honda90** » Sat Apr 05, 2008 12:53 am

I had a 3.7 diff in my 1098 traveller went all the way down to the south of France with it, worked fine acceleration was reduced but high speed cursing much improved. now changed to 1275 acceleration similar to 1098 4.22 diff but much better high speed cursing

Post by **bigginger** » Sat Apr 05, 2008 1:15 am

"high speed cursing" - is it THAT bad?
a

Post by **MoggyTech** » Sat Apr 05, 2008 9:56 am

bigginger wrote:"high speed cursing" - is it THAT bad?
a

Post by **bmcecosse** » Sat Apr 05, 2008 6:39 pm

3.7 diffs sell well - I would say a 3.9 better for general use - but if the 1098 is being 'pepped up' a bit it will pull the 3.7 just fine - and certainly ideal for that future upgrade to a 1275 engine!

Post by **aupickup** » Sat Apr 05, 2008 7:18 pm

it is a brand new one i have as well
will see how much i get for it then and may decide the 3.9 route

Post by **AndrewSkinner** » Sun Apr 06, 2008 8:45 pm

what do you guys think of putting a 3.7 in a 948cc?

I too am going to france and so will be doing allot of motorway miles?

I will not be cruising at faster than 70mph? will there be much difference between the 3.9 and 3.7 at this speed?

I will be wanting to keep the diff in as permanant thing so it needs to be usable but a bit slower acceleration will not kill me!

Post by **Peetee** » Sun Apr 06, 2008 9:06 pm

what do you guys think of putting a 3.7 in a 948cc?

Not a hope. It just doesn't have the torque.

Post by **wanderinstar** » Sun Apr 06, 2008 9:07 pm

I have a 3.7 in a 1098. To start off with I fitted 13" wheels to bring the gearing back down to equivalent of a 3.9. Worked well, but since then I have upgraded engine. 206 head, 1 3/4" SU, SW5 cam and sports dizzie. Now pulls well with 14" wheels back on. No problems.
Wouldn't put one in a 948 though.

Post by **AndrewSkinner** » Sun Apr 06, 2008 9:18 pm

ok. sorry for all the posts! I have just fitted a 4.22 to my morris (with the 948cc engine). It used to have a 4.55 Will i notice a difference with the revs at around 65-70mph? will it cope better with this diff in it and will i notice an increase in mpg?

Thanks for your help! Im just about getting my head round this now

Post by **bmcecosse** » Sun Apr 06, 2008 9:39 pm

It will cope fine if you are 'pepping' up the engine a bit. I can't remember what engine mods you have ? The fuel consumption will hardly vary. Longer gearing forces you to have the throttle wider open to get the same power at lower revs. the cylinders are then getting more complete filling = higher 'barometric' (or some call it dynamic) compression ratio which gives higher efficiency. Best for economy is high 'volumetric' compression ratio to start with - which is why the 998 Mini ended at 10:1 in standard form, and this is what you should aim for. Usual mods to cylinder head etc are all aimed at getting more air into the engine - done sensibly with a tame(ish) camshaft will give best mpg IF the car is driven sensibly! If you use the extra power to go faster - well, the fuel consumption will suffer. Ideal for a 948 (for a little extra power with economy) is to fit the 1098 camshaft (AEA 630) and the 1098 (12G202) cylinder head after it has been skimmed by as near to 100 thou as you dare - and some light air-flowing work in the valve throats. Keep the standard carb to limit the extra power and to maximise gas speed through the carb for best possible atomisation of the fuel - but with a better flowing air cleaner. Dizzy will need to be tweaked for best timing at all speeds (or go Megajolt) and the vacuum advance checked to make sure it's working properly.

Post by **Peetee** » Sun Apr 06, 2008 11:09 pm

As a comparison, a 948 with 12G295 head, 1.5" carb, alloy inlet and stainless exhaust with a 4.55 diff pulls better at all revs than a standard 1098 car. It is also a lot smoother at all revs. So that sort of spec would easily cope with a 4.22 at speed - although unless you are intending to spend a lot of time at 70mph I can't see the point 'cos you would loose the advantages everywhere else.

Post by **bmcecosse** » Mon Apr 07, 2008 7:27 pm

With your engine spec Peetee you could usefully pull a 4.22 diff.

Post by **moggiesgalore** » Mon Apr 07, 2008 9:47 pm

I ran my mog with a 3.7 diff and 1098 engine for a while and it worked quite well. I just had one instance where the car refused to pull up an EXTREMELY steep hill after changing into first. Having said that the car now has a 1275cc Ital engine.

Post by **Peetee** » Mon Apr 07, 2008 11:03 pm

With your engine spec Peetee you could usefully pull a 4.22 diff

I'm sure you're right but I don't have the car now. Besides with the sort of driving I did a 4.55 was fine and the gear ratios with a 1098 box were spot on for enthusiastic driving.

Post by **bmcecosse** » Tue Apr 08, 2008 7:16 pm

Indeed - just a shame about the steeply rising cost of petrol!

Post by **rayofleamington** » Wed Apr 09, 2008 4:39 pm

My 71 pick up has a 3.7 diff. The 1098 engine is in poor nick but it still goes well enough. Hills are not good as you loose a lot of speed but cruising on main roads and motorways is much improved. The Lands-End Orkney run was no hassle at all.

Given a fair choice I'd go for a 3.9 but these used to be equally pricey and hard to get.

Post by **dunketh** » Wed Apr 09, 2008 4:41 pm

The trouble with 3.7 diffs is finding the ruddy things!

Those that do appear often cost more than the engines that drive them.

I love the new 'mgf wheeled' look. Any chance of a better picture?
Your 4 door is looking like how I wanted to do my 4 door - only I never had the misses permission to spend money on it!

Post by **aupickup** » Wed Apr 09, 2008 6:11 pm

selling my 3.7
will try for a 3.9