Diff ratio for a full race 970

[Vegard]

That's the question basically.
4.6? Lower?

[davidnutland]

How about a 4.9 I have one in stock!

[rich@minispares.com]

I had a 5.3:1 once

[ivor badger 2]

tyres? track? RPM limit?

[Vegard]

tyres? track? RPM limit?

Yes, it does have tyres, and it should be run on the track

RPM limit.....What is it, 9000?

It's for a FIA car, so CR65s.

[rich@minispares.com]

I run a 4.3 in my 1071 and its perfect

I suppose a 970 would take something higher, but it will depend on the length of the track and if your wanting to really pull its ears back

[Vegard]

Norwegian and Swedish tracks are not so "long" as English ones, so I guess I could go a bit lower here.

[360gts]

OK...your car is a 970...our car was a high revving 1071 Longman.....we used the SC C/R Leyland gears....reduction drop gears...our best results came with a 4.1:1 C/W
The engine revved consistently to 10K...with peaks to 10.8K
We used Dunlop 10" Slicks....most of our tracks were around 2 miles+/-...
What you have to be concerned about is not the length of the track overall...more....what is the longest straight.
That is where you have to take into consideration for reliability....you may have to comprise on the C/R ratio for reliability on a 970. Remember you will not have the torque of the larger S engines.
Final point, with drop gears other than 1:1...you will risk over-revving a 970.

[ianh1968]

I run a 4.3 in my 1071<SNIP>
I suppose a 970 would take something higher,<SNIP>

... or do you mean "lower"...

Higher number = lower gear
Lower number = higher gear

Rich, please re-state or confirm your bid.


Do you mean go for a 4.5, or a 4.1?

It's important to get the distinction right here!
In my view a "higher" diff gives a higher gear ratio,
and has a lower number.
i.e. It's one that will give more relaxed cruising etc.
(... or less revving the testes off it!)

Ian

[Vegard]

I agree. Low diff is 5.1:1. High diff is 2.76:1.

[almondgreen]

It is easier to say short or long...

[Vegard]

It is easier to say short or long...

Not really as all of my CWPs are EXACTLY the same length

[almondgreen]

[rich@minispares.com]

Not really as all of my CWPs are EXACTLY the same length

that's not technically true, as some of the competition ones have different hole centres, which can cause problems if the back of the gear case/bearing locators have been refaced as it shoves the crownwheel further into mesh and chews the pinion up really quick.

you should always blue the teeth and check them......

[dutchacme]

For a typical 970 S I guess you would have 102.5 hp at the flywheel which translates to about 89 hp at the wheels (sccr, semi helical and straight cut transfer gears) the max speed for a round nose Mini having the 102 hp on tap is subsequently 109 mph (174.4 kmh).

The revs for three alternative final drives to reach 109 mph under the provision that 102 hp will be available for each respective rpm will be:

4.35 will return 8351 rpm
4.50 will return 8642 rpm
4.60 will return 8834 rpm

Don’t get carried away with the revability of a 970 when it comes to up shifts, these shift points will be dictated by at which rpm the max torque will occur. Ideally after you have shifted up you want to see an increasing torque with increasing revs. This is all seen purely from the engine, for sure with a 970 you can just hang on a tad longer if required from track or race tactics.