8 replies to this topic

[bigian]

Ideas please..


I have been playing with the idea of building a MK3 850 rally car for use in the HRCR road rallying championship (Historic), However after 14 years of not owning a Mini i am back trying to get my head around what is what. I have been advised that the 12g940 head is alowable for these events!

Can anyone sugest a level of engine spec/tune that would give the car some more power but with reliability.Also ifanyone has ideas of gearbox spec and any other mods that are period.

Thanks for you help in advance.

[Teapot]

Cooperman is probably your man. He will probably be along directly to advise.


*Directly is a west country term for not-sure-how-long

[Cooperman]

My early rallying was mainly in 850 Minis, but by today's standards they were sooooh slow. The works pepared 850's had about 50 bhp and it would be hard to get much more than that with any degree of reliability. Maybe 55 to 58-ish is a possibility.
Apart from the engine mods, are you now allowed disc brakes as a 'period modification'? If so, are 'S' brakes allowed? Early 850 rally cars had single leading shoe front brakes and we used to fit Ferodo VG95 or Mintex M4 linings. They still didn't stop too well, but everything is relative and they didn't go fast either. Questmead Limited of Rochdale would be the best people to advise on friction material.
With regard to the engine, the weak points are the split-skirt pistons, the fact that the cam runs directly in the cast iron block with no cam bearings, and the crankshaft. You could ask F.W. Thornton of Shrewsbury for advice on what alternative pistons are available and ideally flat-tops with solid skirts would be good. If you can find someone to do it, it is possible to have the block line-bored for proper cam bearings. Rob Walker at Witney, Oxon might be able to help.
Your best bet for a head is really a 12G295 Cooper head as then you can run a better cam without pocketing the block. You could go up one valve size, although at 850 that might not be necessary.
The biggest issue, however, is always going to be the 850 crank. There was a stronger competition 850 cam back in the 60's, but finding one now would be difficult. Using the standard crank as a basis, even with balancing and tuftriding your safe crank rev limit is still going to be around 6200 max. That will determine the cam and probably a Kent 256 would be OK. As for compression ratio, maybe a maximum of 9.75:1 would be about right, bearing in mind the other limitations.
From there, gas-flow the head, use twin HS2 carbs on a decent inlet manifold, fit an original type Cooper 3-branch exhaust manifold, a small-bore exhaust system, ideally 1.625" internal diameter. In fact, a standard Cooper 998 exhaust would be fine. An Aldon 'Yellow' distributor would also be a good idea as you do have to run points ignition.
If you do those things it should be reliable. Make sure you get a low-mileage crank if you can, then balance it, lighten the flywheel and fit a really good crankshaft damper (the original 850 had just a pressed-tin one!).
I think you could stick with the original gearbox unless you could get a set of Mk. 1 Cooper/Cooper 'S' gears to fit into the box. 'Guess works' may be able to help. There is no point in going to 'straight cut close ratio', as you won't have a hot enough cam for it to be necessary. Stick with a 3.76:1 final drive as it's ideal for an 850.
Good luck with the project. It would be good to see a genuine early 850 out there competiting again.
If you have more questions, or even if you just need a completely original 850 engine and gearbox, PM me.

Peter

[bigian]

My early rallying was mainly in 850 Minis, but by today's standards they were sooooh slow. The works pepared 850's had about 50 bhp and it would be hard to get much more than that with any degree of reliability. Maybe 55 to 58-ish is a possibility.
Apart from the engine mods, are you now allowed disc brakes as a 'period modification'? If so, are 'S' brakes allowed? Early 850 rally cars had single leading shoe front brakes and we used to fit Ferodo VG95 or Mintex M4 linings. They still didn't stop too well, but everything is relative and they didn't go fast either. Questmead Limited of Rochdale would be the best people to advise on friction material.
With regard to the engine, the weak points are the split-skirt pistons, the fact that the cam runs directly in the cast iron block with no cam bearings, and the crankshaft. You could ask F.W. Thornton of Shrewsbury for advice on what alternative pistons are available and ideally flat-tops with solid skirts would be good. If you can find someone to do it, it is possible to have the block line-bored for proper cam bearings. Rob Walker at Witney, Oxon might be able to help.
Your best bet for a head is really a 12G295 Cooper head as then you can run a better cam without pocketing the block. You could go up one valve size, although at 850 that might not be necessary.
The biggest issue, however, is always going to be the 850 crank. There was a stronger competition 850 cam back in the 60's, but finding one now would be difficult. Using the standard crank as a basis, even with balancing and tuftriding your safe crank rev limit is still going to be around 6200 max. That will determine the cam and probably a Kent 256 would be OK. As for compression ratio, maybe a maximum of 9.75:1 would be about right, bearing in mind the other limitations.
From there, gas-flow the head, use twin HS2 carbs on a decent inlet manifold, fit an original type Cooper 3-branch exhaust manifold, a small-bore exhaust system, ideally 1.625" internal diameter. In fact, a standard Cooper 998 exhaust would be fine. An Aldon 'Yellow' distributor would also be a good idea as you do have to run points ignition.
If you do those things it should be reliable. Make sure you get a low-mileage crank if you can, then balance it, lighten the flywheel and fit a really good crankshaft damper (the original 850 had just a pressed-tin one!).
I think you could stick with the original gearbox unless you could get a set of Mk. 1 Cooper/Cooper 'S' gears to fit into the box. 'Guess works' may be able to help. There is no point in going to 'straight cut close ratio', as you won't have a hot enough cam for it to be necessary. Stick with a 3.76:1 final drive as it's ideal for an 850.
Good luck with the project. It would be good to see a genuine early 850 out there competiting again.
If you have more questions, or even if you just need a completely original 850 engine and gearbox, PM me.

Peter

Peter,

Thank you for your time to put together this spec list i am very greatful. I just hope that i can now source the parts and make a go of it..


Thanks again

Ian.

[bigian]

My early rallying was mainly in 850 Minis, but by today's standards they were sooooh slow. The works pepared 850's had about 50 bhp and it would be hard to get much more than that with any degree of reliability. Maybe 55 to 58-ish is a possibility.
Apart from the engine mods, are you now allowed disc brakes as a 'period modification'? If so, are 'S' brakes allowed? Early 850 rally cars had single leading shoe front brakes and we used to fit Ferodo VG95 or Mintex M4 linings. They still didn't stop too well, but everything is relative and they didn't go fast either. Questmead Limited of Rochdale would be the best people to advise on friction material.
With regard to the engine, the weak points are the split-skirt pistons, the fact that the cam runs directly in the cast iron block with no cam bearings, and the crankshaft. You could ask F.W. Thornton of Shrewsbury for advice on what alternative pistons are available and ideally flat-tops with solid skirts would be good. If you can find someone to do it, it is possible to have the block line-bored for proper cam bearings. Rob Walker at Witney, Oxon might be able to help.
Your best bet for a head is really a 12G295 Cooper head as then you can run a better cam without pocketing the block. You could go up one valve size, although at 850 that might not be necessary.
The biggest issue, however, is always going to be the 850 crank. There was a stronger competition 850 cam back in the 60's, but finding one now would be difficult. Using the standard crank as a basis, even with balancing and tuftriding your safe crank rev limit is still going to be around 6200 max. That will determine the cam and probably a Kent 256 would be OK. As for compression ratio, maybe a maximum of 9.75:1 would be about right, bearing in mind the other limitations.
From there, gas-flow the head, use twin HS2 carbs on a decent inlet manifold, fit an original type Cooper 3-branch exhaust manifold, a small-bore exhaust system, ideally 1.625" internal diameter. In fact, a standard Cooper 998 exhaust would be fine. An Aldon 'Yellow' distributor would also be a good idea as you do have to run points ignition.
If you do those things it should be reliable. Make sure you get a low-mileage crank if you can, then balance it, lighten the flywheel and fit a really good crankshaft damper (the original 850 had just a pressed-tin one!).
I think you could stick with the original gearbox unless you could get a set of Mk. 1 Cooper/Cooper 'S' gears to fit into the box. 'Guess works' may be able to help. There is no point in going to 'straight cut close ratio', as you won't have a hot enough cam for it to be necessary. Stick with a 3.76:1 final drive as it's ideal for an 850.
Good luck with the project. It would be good to see a genuine early 850 out there competiting again.
If you have more questions, or even if you just need a completely original 850 engine and gearbox, PM me.

Peter

Peter,

Thank you for your time to put together this spec list i am very greatful. I just hope that i can now source the parts and make a go of it..


Thanks again

Ian.

[bigian]

What other heads would be a possability?

[Cooperman]

You could fit a 12G940, but as you'll want a decent cam with higher lift, you would need to machine pockets in the block deck. A 12G295, suitably 'improved' would certainly be best for power in an 850. Alternatively it would be possible to modify a standard 850 or 998 head with full gas-flowing and bigger valves. After all that is what rally Minis had in the early 850 days. It is unlikely that any 850's were used competitively after about 1963. I rallied in one during 1963 and won the London Counties Championship in it, but that was as a navigator and my driver, Bill Rogers, was an outstanding Mini driver. His Mini, 9NKP, must have been one of the most successful and long-rallied 850's ever. In early 1964 he got a big-engined Anglia and I got a 998 Cooper, both of which Bill drove very quickly on various events up to National level.

[bmcecosse]

Why 850 ? A 998 will be SO much better!

[Cooperman]

Why 850 ? A 998 will be SO much better!

For HRCR events a 998 Cooper would cost a lot more than an 850 and it would be just another 998 Cooper.
No-one has used an 850 for HRCR road rallies for at least 12 years and it would be both interesting and evocative to see one out again. It might not be competitive with the Cooper and Cooper 'S' variants, but it would stack up well against Rapiers, TR2's & 3's, MGA's, and other early 60's stuff. 850 is where the Mini started in competition after all.