Differential Ratios

[Richard G]

What are advantages and disadvantages of the ratios 3.7 or 3.45? What is standard?

[richard w]

Hi Richard.
3.7 will give better acceleration, 3.45 will give lower revs - more relaxed cruising. Not sure which is standard, I'm sure someone more knowledgable will be along soon!

Richard

[keeny]

3.7 is standard and best suited to manual gearbox,3.45 fitted by some people to bring the revs down on auto box stags
Phil

[Ian Durrant]

3.7 is standard. Some people have fitted 3.45 to Borg Warner 35/65 automatics to reduce the revs on motorways but the sparkling performance the stag is credited with, is reportedly affected. The best of both worlds is achieved by changing the auto box to a ZF 4 speed but that is a pretty expensive option.

I would expect that a 3.45 on a manual overdrive probably does not give enough advantage in either direction to be worthwhile.

Hope that helps

Kind regards
Ian

[Rubce]

We have a 3.45 fitted to MOD. It knocks a few hundred revs off so helps fuel consumption, engine noise and wear etc. Previously had a 3.7 fitted to the car but we will staying with the 3.45. It's all down to personal preference.

Cheers

Bruce

[DJT]

I had a 3.45 in my old MOD Stag. It is now in my BW35 Stag. Works fine in both cases.

[milothedog]

Any help, I believe from Dave DJT the difference is 7%

Maths and me But if you say a BW35 equates to 20mph for every 1000rpm x 3 = 60 mph


7% of a 1000 is 70 so 930 x 3 = 60mph with a 3.45 diff

So at 60mph your engine is doing 2790 rpm, sound right or am i talking B******ks


So 210 rpm less.

Ian

[BartonStag]

Going off on a slight tangent with this one folks....... but. My diff has a leak i'll need to remedy, but can someone please tell me how to identify which ratio is fitted when I get round to doing it, or following on from this thread - changing it.
Cheers
Gord

[Mike Stevens]

If 20MPH/1000 with a 3.7, that should make 20 * 3.7 / 3.45 for a 3.45 = 21.45 MPH/1000.

Or, 3000RPM * 3.45 / 3.7 = 2797RPM @ 60MPH with a 3.45.

Shouldn't it?

Brain fade today. (So, what's new?)

Cheers,
Mike.

[DJT]

Does this help? http://www.mintylamb.co.uk/gearspeed/

For the 3.45 diff use 2.5/2.5PI (MD/MG/MGA)
For BW35 use the 2000/2500/2.5PI Automatic option

[mike@thenook]

Does this help? http://www.mintylamb.co.uk/gearspeed/

For the 3.45 diff use 2.5/2.5PI (MD/MG/MGA)
For BW35 use the 2000/2500/2.5PI Automatic option

Thats a useful tool Dave,

Seen the one for converting tyre sizes/rims but this could be very handy too - good research

Cheers!