Which Final Drive Ratio?

[Gedon]

You have a 1430 engine with a lumpy cam, big weber and ST ratio gears. You have noticed this ad on ebay

http://cgi.ebay.co.uk/Mini-Cooper-Straight-Cut-LSD...

Noise isn't a problem as you will be wearing earplugs anyway. You want the best combination of accelleration and top speed for A/B road silliness.

The toss up is 3.44-3.7

Edit:- Whilst not being totally full race, the car lost any attempt at being civilised years ago.

Edited by Gedon on Monday 14th September 13:54

[haynes]

go with the 3.7, that what i use on the road with a sccr box, 10 inch wheels. Great on a and B roads, really not fun on a motorway though.

[Gedon]

The guy on eBay makes SC LSD crownwheels and mine being a 4.3 Semi has to go.

The 3.7 has a bigger, stronger pinion than the 3.4, I think.

Cheers!

[GingerWizard]

Gedon said:

Edit:- Whilst not being totally full race, the car lost any attempt at being civilised years ago.

Edited by Gedon on Monday 14th September 13:54

I like that very much. Mine was'nt civilised either, they get like that dont they.....!!?? hehehe made me smile......;)

[guru_1071]

i would be very careful, as the items this guy is selling are certainly not the same as those offered by minispares (or any of the larger specalists).

most after market c.w.ps are semi helical, the only one that was ever traditionally s/c was 3.7:1, which was the one used in mini 7 racing years ago. they are not suitable for use in large power cars as they just tear to bits in no time.

s/c c.w.ps make a horrific screaming noise and will need a new pinion about every 500-1000 miles as the pinions are virtually a sacraficial part (this is the same in semi helical, but they do tend to last a while longer), you have to run a trade off of either hardenening them to make them last and run a risk of teeth breaking off, or softer to retain core stabilty.

also claiming that a c.w.p will fit 'any' lsd is wrong. you normally have to 'size' the crownwheel to the case of the lsd, so if the ones on ebay have been made to suit a sailsbury (the largest case type) then they will not locate on tran-ex's or minispares evo diffs - rather they will only locate on the bolts, which is not good practice, as its very difficult to ensure that the crownwheel is correctley centred on the diff case.

id would be asking the seller what warrenty he offers, and if he will sell the pinions on their own as you will certainly need one as a spare.

[Gedon]

I've had the box to bits to have a look and after a good count, I've got a 4.1 in there.

Hmmmmm.....what to do. I'll have a play with the ratio calculator.

Looking at the way the semi-helical meshes, it may as well be SC. I bet they are noisy as well. I'll be wearing some decent ear plugs anyway.

[guru_1071]

the semi-helical arnt nearly as bad as its all to do with the tooth form and how they mesh together plus the back lash thats built into the gears. a lot of the scraficial wear that occurs is due to the tooth count on the pinon as they are are so small in the lower ratio cwps.