19 replies to this topic

[dwealds]

Hi, I own an Mpi but I do quite a lot of motorway driving and it annoys me that without revving the engine a fair bit i dont keep up with the traffic. So i was wondering if anyone had heard of or knows anyone that has or can install an overdrive kit for my car?

Cheers

[Paul Wiginton]

The JKD 5 speed is an overdriven gearbox, other than that, no.
You could change your diff ratio to give better motorway cruising speeds. If you have a 3.4 for example you could fit a 3.2 or 3.1 to give a higher top speed or reduce revs at a given speed.

Paul

[nicksuth]

I have a 5 speed box with 5th giving 21mph per 1000 revs, i.e. 4000 rpm = 84mph ideal cruising speed on the motorways if you want to keep up with average midle lane traffic?

[dwealds]

Ok, cheers guys. Don't suppose you know the standard diff ratio for an Mpi?

[Asphalt]

2.76:1 - longest ever used

[nicksuth]

Ok, cheers guys. Don't suppose you know the standard diff ratio for an Mpi?

MPi Diff is 3.213:1 - 4th should give give 17.8 mph per 1000 rpm

[Asphalt]

No! MPIs got a 2,76:1! The 3,21 was fitted to some SPIs...!

[nicksuth]

Rover Manual is wrong then (not unknown!!) - here is screen dump from page.

[attachment=88879:MPi_Final_Drive.JPG]

[Asphalt]

Hummm... That's odd... The handbook indeed says 3,21 (just had a look to the german edition)...

[dwealds]

Im not sure what I have then as when im in forth doing 60 its around 2800rpm so cant be the 3.213:1 as that equals 54mph. Guess the speedo could be out though. Anyone got any idea about prices for the JKD 5 and 6 speeds? I know they are really expensive judging by Minispares being £2000

[Sprocket]

All UK MPi 1997> models were fitted with the 2.7:1 Final Drive to reduce driveby noise and improve motorway crusing comfort.

The KAD 5 speed box is £2898 and the JDK or KAD 6 speed is NLA

The KAD 5 speed is a racing box with close ratios, tall first, 1:1 fourth and straigt cut gears. This will not improve your driving comfort .

You could consider fitting 'Economy' transfer gears, this should reduce down the gearing a little at not much extra cost.

60mph at 2800rpm mine does 60 mph at 4000rpm

[nicksuth]

Im not sure what I have then as when im in forth doing 60 its around 2800rpm so cant be the 3.213:1 as that equals 54mph. Guess the speedo could be out though. Anyone got any idea about prices for the JKD 5 and 6 speeds? I know they are really expensive judging by Minispares being £2000

Have a look at Guessworks ratio calculator - Guessworks

[norwegianminiman]

Any idea what the standard ratio of an SPi is? going to be rebuilding the gearbox soon and may be fitting an LSD...

[Ethel]

Another thing to look up on Guessworks site. You'll only be able to use the original final drive with a Quaife ATB.

[Sprocket]

Again, been asked a million and one times.

Non Cooper SPi has a 3.1:1 final drive

Cooper SPi has a 3.2:1 final drive.

You should be able to get a standard crown wheel modified to fit the Quaife, no problem.