Lowering the RPMs

The 3.44:1 final drive is great for acceleration, perhaps a little too good: full throttle is unusable in 1st gear, and you have to take care in 2nd in the wet. But the main issue is doing 4000rpm at 100kph. It’s not very relaxing. So I’m biting the bullet and rebuilding the gearbox with a 2.76:1 final drive, as fitted to the late ’90s Minis.

I’ve also got a Kent 246 “high torque” cam, but the existing MD266 is already quite torquey so I’m going to leave it in and see how it copes. I can always change the cam later. Right: remove engine, rebuild gearbox.

While the gearbox is apart I’ve also put new springs in the synchro hubs (not enough tension on the old springs so it was grinding into 3rd), smoothed out the selector rail detent notches (now wave shaped for smoother shifting), and shimmed the layshaft to spec by putting shims behind the small thrust washer.

As expected, acceleration is very much reduced. On the other hand I can get to 100kph in 2nd now, so 0-100 time is about the same. The MD266 cam seems to be just fine, with enough torque to pull well in any gear.
Here’s the road speed/rpm graph thanks to Guess-Works online Mini gearbox calculator (Original final drive is in green, new 2.7:1 is in white)

3rd gear is for overtaking and cruising around town, 4th gear feels like 5th in a modern car. Nice and (relatively) quiet for cruising. I call this a success.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s