Can anyone who has done Targa Tasmania or similar in a Mini give me some advice as to which diff ratio we should be running?

I have a 1071cc engine (new), close ratio straight cut gearbox, and a salisbury lsd. The ratio that came in the diff was 3.1 which I am thinking might be too high.

I believe the engine will rev to around 8000rpm - but I'm thinking we wouldn't like to rev it that hard for reliability reasons.

Interested to hear any advice.

For what it's worth, standard diff in a 1071S was a 3.76:1.
I've not rallied Tassie, but have driven our ~90HP 1293 (with 3.65 diff) around it- I'd say a 1071 would want a 3.76, or maybe a 3.9.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

The Targa minisport mini has a SC close ratio gearbox, and as I recall he said 3.76 worked best. Due to the close ratio, but this is a big bore 1275, not 1071, so you need a shorter diff to get around quicker.

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1964 Morris 850, 1330 Supercharged - 81.8hp atws.
1975 Leyland Mini S 1100S powered - Nice and reliable.
1977 Leyland Mini LS - Project LS-T

Hi, i just did Targa in a mini which i built as a 64 Cooper S, 1310 engine which ran a standard 4 syncro gear set. i used a 3.7/1open diff. 1275 torque worked ok with std ratios, final drive was ideal, run to 8000rpm. But i think as Dr mini said a 3.9/1 would be good in a small-er bore. I just would think twice about running LSD, a real hand full in tarmac rallys. I did rally Tas also and run open diff aswell, wheel spin wasnt a big issue.
Currently building a 998 Cooper for next year, may use 3.9/1 or 4.1/1final drive.
Mini sport mini, sccr box, open diff, 3.7/1. Happy mini-ing.

I've had a lot of mixed opinion's on the LSD. I have the LSD in my new engine but havn't driven it yet. The old 1100 had a lot less HP than the 1071 is going to make and wheel spin was an issue with it. What ill effects should I expect?

so we're getting a 3.9 or 4.1 open diff then bricknut?

The shoirt stroke engines love to rev, therfore they like zippy diffs, but Targa Tassie has a fair amount of very open very fast top speed sections (as well as a heap of tight & twistys too) so a compromise would be the go & i`d suggest a 3.7

I ran a 1510cc at Targa Tasmania 2002 & used a 3.2 with it, but only cause it was a road engine with very very torquey & very broad power spread yet still happilly reved past 7500, so it wasn`t a bad set up. I`d have rathered a few more revs but again a compromise on power verses reliability is the go for Targa Rallys if you want to finish. We sat on over 100mph for quite a long time on Mt Arrowsmith stage (nearly 15mins actually) & many many other stages demand huge top speed too, so don`t go tooo zippy if you can avoid it.

& i would use a limited slip diff, but i`m very used to them & lockers & have driven with them nearly all my life,,, if you`re not used to it then get lots & lots of practise with it before you go ,,, or don`t use it.

Have fun man, it is a total blast i can assure you

But remember the age old saying---> "To finish first, first you must finish"

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No offence intended here but--> anyone writing a book about minis 30 years ago may not have experienced such worn or stuffed-with components as we are finding these days.

You should put your heart & soul into everything you do.

G'day Bricknut, The only classic Mini that I remember competing against in this year's Rally Tasmania was Graeme Robinson / Bruce Robinson in a 1978 Leyland Mini Clubman S. I believe it was running a KAD 5-speed box which had selector problems and put them out of the event after Day One.
Which car was yours?
As for diffs, I agree with MiniMan, it would be advantageous to use an LSD and a 3.7 ratio would be my choice as well, but how easy they are to drive depends a lot on the type of LSD and how tight it's set up. I run a Quaife in my Cooper 'S' and am quite used to it's characteristics, and although it's set up quite soft it can still catch you out by 'tram-lining' if you aren't concentrating.

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Curly
'64 Cooper 'S' (Group Nb spec)
'67 Mini Marcos GT www.mm7056.wordpress.com

The problem I have is that its all assembled and ready to go with the 3.1. If its definitly not going to pull it though, it'll be easier for me to change it now rather than after the engine goes into the car. Does anyone know where I can get the Salisbury diff gears from? The 3.76 sounds like the goods.

I have a Salisbury old school LSD which was re-built by Auto Spiral Gears in Adelaide. I'm not sure how they set it up, I told them what I'd be using it for though. They put new plates etc into it so hopefully it'll be good.

Everyone has contradicting opinions on these things. Some people say LSD, no lsd, quaife, no quaife, salisbury, cone type.... I'm just going to pick a ratio and drive it

Can anyone tell me what sort of bad characteristics I can expect from the LSD? I'm assuming that it'll induce understeer while on the power?

Matt how much 100mph stuff can I expect in Tassie? I've just done the Suncoast and we got up around 200km/ph, but this was in a 240HP Lotus Exige. Not a 100hp Mini Cooper... I think the trends are going to be towards limiting those high speed sections in the future. In which case if this might happen - should I be going a 3.9?

Drmini - although the engine will rev, I certainly don't want to be revving the ring out of it for 5 days. The engine has cost me a fortune so I'm going to want at least a few targa's out of it.

I've hill climbed with a 3.76 on an 1100 and it was barely acceptable. 2nd gear was too low and 3rd was too high. Options, go to say a 4.1 and pull 3rd gear, or goto a 3.4 and have enough in 2nd gear that I don't have to change. Every time you change gears you loose 1 second. Based on this, am I better with a higher ratio diff that'll give me more speed range in each gear, or do I want to be cog swapping all the time on something lower?

I'd go with a 3.76 then. Or maybe a 3.647 (Mini-K ratio). with the latter and 10" wheels, 110KMH = 4,400 rpm approx.
I like this ratio for general hooning.....

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

Sounds like you need a close ratio gearbox!
Safety concerns have led to high speed sections being reduced on tarmac rally stages through the use of chicanes, but it's still easy enough to reach 160+ just not sustain it for any length of time.
Another point to consider is your comfort and sanity during the transport stages which can be quite lengthy. The last thing you want is to sit at 5000rpm on the highway speed limit between special stages.

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Curly
'64 Cooper 'S' (Group Nb spec)
'67 Mini Marcos GT www.mm7056.wordpress.com

Curly this is a very valid point. What ratio gets your vote?

I'm running 10" wheels, close ratio straight cut gearbox.

Does anyone have a ratio calculator? I think if I can gear it for a top speed of somewhere around 110 miles per hour at say 7000rpm?

Anyone know what I can safely rev a 1071cc engine to? It has the propper cooper s crank, standard bearings on the crank (too many varying opinon's on the extra bearning so I didn't do it). I've got good valve springs with pleanty of pressure.

I'm going to run a rev limiter on the car, our plan was to dyno it and set the limiter to cut in just before we start hearing bad noises. Interested for feedback.

You need to download Gearcalc. It makes working out ratios a breeze.

Just having a quick play with Gearcalc and worked out...

3.93 @ 7000rpm = 101mph
3.76 @ 7000rpm = 106mph
3.65 @ 7000rpm = 109mph
3.44 @ 7000rpm = 116mph

That is provided your tyre dia = 19.09"