Morris Minor Owners Club

Hi guys,

I've seen many engine swaps use different diffs to help support the output of the new engine. These often come with entire axle swaps too.

But lets say, purely theoretically... [throws a blanket over the spare 80bhp Zetec SE engine in the garage]

What sort of power could you safely put through a Morris diff, without the need for an axle swap?

Over the many years I have been competing with my Minor (135 bhp plus at the flywheel) I have only had the standard 4.55 diff fail (sun gears) once.
Standard diffs are relatively cheap and widely available and will not break the bank if the need to replace arose.
7" wide slicks are fitted to alloy wheels. The axle is well located and fitted with anti -tramp bars. The half-shafts are heat treated and guaranteed to transmit 178 bhp.
I can easily smoke the tyres even with a S/C C/R gearbox fitted at a standing starts.
With standard half-shafts and no anti-tramp bars fitted I would suggest that the standard Minor axle can cope with around 60 bhp - 70 bhp.

I agree with Phil that you're unlikely to give any standard BMC diff any trouble with those power outputs - and if you did there are plenty of diffs available and easy to change too. I have competed in sprints and autotests too using standard diffs using a well tuned 1340cc Midget engine running through various standard differentials and standard halfshafts too. Been lucky maybe but never broken anything

I’ve only smashed one diff, although the odd half shaft has given out. I suspect that half shafts are the usual weak link in the minor back axle. A diff would likely be already well worn, should it give way.

Diff strength is very much determined by how you drive it, snap start the clutch in and you can generate torques double that of the engine torque.

Sideshafts seem to be the one thing that fails commonly but this more related to fatigue than strength, even standard minors can fail them eventually higher torque will just bring it on earlier.