11 replies to this topic

[rob mini]

right, im having a box rebuilt soon for my new engine and wondering what ratios people would reccomend as im not sure whats available. i want to keep my 3.1 final drive as its not so bad to be cruising along at 70mph at 3.5k rpm. just wondering what ratios to use? i have a couple of spare 'boxs (a series and A+) and wondering if parts are interchangeable.

what diff upgrades would you recommend for around 65-70bhp at the wheels?

[Guess-Works.com]

Are you looking at Helical or SC to start with.

As for the power, you'll be ok with a standard box and diff, you could go up to a X-pin diff, but probably better off just getting the box rebuilt with a Competiion diff Pin and Bearings.

I did a complete rebuild of a box and diff for a mate the other week, and total cost was just about 200 notes.

Have a play with ratios here....

Clicky

[Dan]

Most if not all gearbox parts are not interchangeable from one type of box to another. Just about the only parts which do migrate are the gaskets.

How strong your diff needs to be depends on what you intend to do with it just as much as how much power you're going to stick through it. How big are your wheels and tyres and what kind of driving will the engine be doing? If it's a grasstracker for example then you want a much stronger diff than for a daily driver. As a daily driver with standard rubber you'd want at least a competition pin and bushed pinions as Guessworks said, but if it's for anything more strenuous then I'd definitely say you want a crosspin. Minispares crosspin is a lot better than Minisports in my opinion. I'd never use a bog standard diff now, not when the crosspin is so easy to fit and not really all that expensive.

[rob mini]

its on 13x7's and will be used for an occasional track day but just normal road use otherwise

rob

[Guess-Works.com]

Basically, no matter what ratios you use, your 4th gear is always 1:1 so you motorway speed will not be affected...

The ratios only change between 1st and 3rd..

Modern A+ gearboxes generall have a long first gear, and 2nd and 3rd are much the same as the old A series boxes.

The other choices are close ratio sets of which some of the old GT/CooperS 4 synchro boxes are still around and the layshaft and 1st motion can still be bought new.. Or buying an SC/CR gearset outright.

These are all shown ( and the effect of their use ) on the clicky lnk above...

By the nature of how the mini box is built, the layshaft, 1st motion and gears are all in sets, and essentially you cannot interchange between different types of set. But the Diff and drop gears are.

[Jammy]

I don't really know much about ratios or anything, but won't a different final drive mean you can achieve higher motorway speeds?

[Guess-Works.com]

Yes, but it will take longer to get there... ie longer diff = slower acceleration

I personally hate driving minis on motorways, unless it's absolutely necessary, there's no corners on them, and my left foot feels left out from the party !!!

[rob mini]

th e problem is a travel the country to goto cruises and events and the amount of juice i'll use if my diff is shorter would be unreal id expect!

[Guess-Works.com]

you'd be surprised, I use a 3.44 diff on my 1330, with ickle 10" wheels, and I still return over 35 to the gallon when on long hauls. Putting a longer diff will only save if you do a lot of high speed miles, as the engine needs more power/torque to turn the final drive, you'll find you'll have to be heavier on the right pedal, especially in town driving, where with a short dif you may be able to get away with 3rd or even 4th, with a longer diff you may need to be in 2nd, end result more revs, more fuel.

[rob mini]

im swaying towards the idea of a 3.4 diff very quickly as i have one already to go in. the extra accel with a 3.4 should be a lot better to outweigh the downside of more revs on motorways. just stick to 60mph i guess though

[Guess-Works.com]

60mph, with a 3.4 is smack on the power, 3.5K rpm, to overtake you dont even need to drop to third.

Also an RC40 will just start to hummmmm, and you'll be hypnotised by the sound

[rob mini]

sounds good to me! already bought my exhaust system a while back. a boxer back box from huddersfield mini spares and im going to get a freeflow on it. the hif44 will be on a rampipe too so should sound good