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Finding the diff ratio ?
https://www.ausmini.com/forums/viewtopic.php?f=2&t=89197		 Page 1 of 2
Author:  Phil 850 [ Sat Apr 18, 2015 5:18 pm ]
Post subject:  Finding the diff ratio ?
Hi all
I have found out what my diff ratio is but would like some feedback on the process I used.
As I don't have a tachometer or an accurate speedo and didn't want to pull the engine I did the following.

With the car in 4th gear and jacked up on one side I can turn the wheel and with an indicator on the distributor rotor I could count how many times the distributor rotates. Easy :D
Because you are only turning one wheel the differential will halve the ratio !
Because I measuring at the distributor it rotates at half the engine speed !
So, if I turn the wheel 4 full rotations, i (or in this case the wife) could count the number of rotations of the distributor and I would have exactly the diff ratio 8)

Indicator marked in 18 degree segments (0.05 of a rotation).
Image

The wheel marking point to count its rotations.
Image

4 wheel rotations gave me 4.15 rotations of the distributor so I have a 4.15 to 1 ratio, right :|
Are my assumption correct :?
Author:  Morris 1100 [ Sat Apr 18, 2015 5:22 pm ]
Post subject:  Re: Finding the diff ratio ?
Try it again but with the car on the ground and push it in 4th gear.
Author:  Phil 850 [ Sat Apr 18, 2015 5:28 pm ]
Post subject:  Re: Finding the diff ratio ?
Then it should only be 2 rotations of the wheel to allow for the half speed of the distributor right :|
Author:  Phil 850 [ Sat Apr 18, 2015 5:41 pm ]
Post subject:  Re: Finding the diff ratio ?
Just wheeled along the driveway and two wheel rotations gave 4.05 at the distributor so allowing for parallax error both results are pretty close to each other.
Author:  Morris 1100 [ Sat Apr 18, 2015 6:10 pm ]
Post subject:  Re: Finding the diff ratio ?
The nearest diff ratio to that would be a 4.1.
Which is a fairly useless road diff in a Mini.
Author:  Phil 850 [ Sat Apr 18, 2015 6:40 pm ]
Post subject:  Re: Finding the diff ratio ?
Morris 1100 wrote:
The nearest diff ratio to that would be a 4.1.
Which is a fairly useless road diff in a Mini.

Useless is an understatement.
I'm considering something around 3:1. It is an 1100S so it should pull that OK I think.
Author:  Bubbacluby [ Sun Apr 19, 2015 12:35 am ]
Post subject:  Re: Finding the diff ratio ?
Mates runs a 3.1 in his cooper s and it still goes really well.
Author:  Kennomini [ Sun Apr 19, 2015 9:36 am ]
Post subject:  Re: Finding the diff ratio ?
I can't comment on how to find your current diff ratio but I do have a 3:1 in my car and I love it. It still has good acceleration and is great on the highway.
Author:  MiniVLT [ Sun Apr 19, 2015 10:50 am ]
Post subject:  Re: Finding the diff ratio ?
4th gear is 1:1 so whatever your diff ratio is will be 2 x the dizzy rotation since the dizzy rotates at half the engine speed!

With the car in 4th gear and the road wheel turned 1 revolution, the dizzy should have turned 2.05 times for you 4.1:1 diff ratio yeah?

Cheers Shane
Author:  Phil 850 [ Sun Apr 19, 2015 5:10 pm ]
Post subject:  Re: Finding the diff ratio ?
Thanks Bubbacluby, Kennomini & MiniVLT for the info on diff ratios.
I'll have to chase up a 2.95:1 or a 3.1:1.

Phil
Author:  9YaTaH [ Mon Apr 20, 2015 12:29 pm ]
Post subject:  Re: Finding the diff ratio ?
Interesting outcome ...hope you pulled the plugs before pushing in 4th :D
Author:  Morris 1100 [ Mon Apr 20, 2015 12:38 pm ]
Post subject:  Re: Finding the diff ratio ?
9YaTaH wrote:
Interesting outcome ...hope you pulled the plugs before pushing in 4th :D


Why? It will push quite easily in 4th.
Author:  9YaTaH [ Mon Apr 20, 2015 5:53 pm ]
Post subject:  Re: Finding the diff ratio ?
Morris 1100 wrote:
9YaTaH wrote:
Interesting outcome ...hope you pulled the plugs before pushing in 4th :D


Why? It will push quite easily in 4th.


Oh sorry Mike, didn't allow for your clapped-out, needs new rings, lots of blow-by, low compression engine :P :lol:
Author:  Phil 850 [ Mon Apr 20, 2015 6:03 pm ]
Post subject:  Re: Finding the diff ratio ?
Yes, pulled the plugs otherwise I might've needed a new ring :(
Author:  Mick [ Mon Apr 20, 2015 7:47 pm ]
Post subject:  Re: Finding the diff ratio ?
:lol:
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