39 replies to this topic

[thebrownproject]

I'm looking to pull my 850 off the road next year, once the insurance has run out and doing a full restoration. Picking up ideas on engine spec, I want to do an engine like the ones run in a formula 850 which I believe had up to 60BHP. Yes of course I could fit a bigger engine But that take no skill.

 

I'm looking for advice on what cam to run and what crank is advisable, also what is needed to allow these up rated parts to be fitted, as I know the 850 is missing parts that a 1000 would have such as cam bearings, Money is out the question really as id like to do it over time.

 

I have already got a 12g125 head which I will have skimmed and cleaned up.

 

Its just the cam and crankshaft I'm puzzled with and whether I can fit a 1000 crankshaft and con roads to improve strength and power.

 

Any advise would be much appreciated as I know many people on this forum will have worked with powerful 850 engines and will be able to point me in the right direction to what I need to be getting to re-create a powerful 850.

 

If so if anyone already done it I would love to know what bits you used and where you got them from.

 

Thanks Jamie.

 

 

[racingbob]

in mini 7 series using 850cc

 

if I can recall now we used standard crank , 12g940 head pocketed block

 

cam was a 649 gave 63 at the WHEELS

 

only thing is the engine wont last long with the high revs

 

60 at the flywheel would be better and keeping revs to under 7000

[Alex_B]

Cooperman on here would have a lot of information for this idea. 

Just my tuppence worth, from what I know the formula 850 engines tended to use a special crankshaft that could handle high revs and was much much stronger than standard. I believe you will struggle to make any power without snapping a standard 850 crank and I'm not sure that you would manage to get a 998 crank in an 850 block. Aside from that issue you will have a horrible engine if you are going for full race spec, the camshaft profile will need high lift, long duration and lots of overlap to gain the volumetric efficiency required for high power. The issue you will have with these characteristics is at low engine speeds the airflow into the engine will be such that it will struggle to overcome the exhaust gasses leaving th cylinder and make very little power, likely to be flat below 3000 RPM. On the road this would be completely un-enjoyable. If it is for a motorsport series then this doesn't matter as you will be spending all your time above 3k and at full throttle for a lot of the time. 

If it is a fun road engine you are looking for then a mildly tuned / road suited larger bore engine would be a better candidate, after all there is a very good reason why the 850 engine hasn't  been developed since the 997, 998, 1275 engines were released. I have a 998 and a 1275 mini and both are good fun on the roads, a hotter 998 engine with something like an mg metro cam and associated mods such as ported head and balanced bottom end will leave you with a fun car and should satisfy your need to develop some skills or use your skills. 


If you want to go further then you can look into different engine designs such as running a different cylinder head, you have the options of 7 and 8 port heads, and with more work 16v heads from the likes of KAD or Specialist components do a BMW head conversion. The latter is what I am using for an engine I am developing which will be used in sprints, hill climbs and occasionally on the road. 

Hopefully this might give you some things to research and whatnot rather than just put your ideas down the pan. 

[mab01uk]

You might find some of this thread interesting:-

Tuned 850 Engine

http://www.theminifo...ned-850-engine/

Edited by mab01uk, 14 December 2015 - 08:37 PM.

[mab01uk]

Clive Trickey's race Mini started as a 850cc in Mini Se7en, he wrote these famous books on tuning the 850 when he was writing for Triple C magazine in the 1960's.

 

 

 

 

Edited by mab01uk, 14 December 2015 - 08:56 PM.

[Cooperman]

IIRC, 850's giving 60-ish bhp all had the special crankshaft. A standard 850 crank, even fully crack-tested, lightened & balanced is not really safe to rev beyond around 6500 rpm. In fact I've seen them break at far less than that.

With a 649 cam in an 850 you would need well over 7000 rpm available to make it work.

[thebrownproject]

I'm sticking with the 850 as I think it will destroy the car to put a different engine in, what would you have to have done to the crank and block to strengthen it? So it will take high revs.

[Alex_B]

I'm sticking with the 850 as I think it will destroy the car to put a different engine in, what would you have to have done to the crank and block to strengthen it? So it will take high revs.

 
I don't think you could modify a standard one to make it stronger but you could have one made to the same important dimensions in another material such as EN40B Steel. By changing certain features you could increase its strength with some clever engineering and whatnot. This would however cost a huge amount, look at Swiftune and MED for inspiration as they produce custom crankshafts for high performance. I'm not sure they make an 850 crank but could well make a custom one for you for the right money. 

[Spider]

Not wishing to talk you out of this venture, but I do believe in going in to these sort of projects / ventures well armed with information (which is why you've posted here in the first place).

 

I'd just like to put it on the table from the outset that such an engine as you are seeking to build will be very expensive, much more than a moderately tuned 998 or 1275. It would also be not at all nice to drive as a street engine. It would be cheaper and end up with a much better result (in terms of drivablity and longevity) to build a very short stroke big bore engine if you wanted a 'build challenge' but remain around the 850 cc mark.

 

A suitable crankshaft would be in the order of 1000 GBP plus. As others has said, the 850 crank is not very strong (it wasn't designed for much more than 30 HP in mind) and while there are a few things that can be done to it to extend it's life, nothing would make it 'go the distance'. With some machining, the 998 crank will fit the 850 block, however this would then no longer be an 850, but an un-nessessarily expensive 998, if you are going to go down this road, save the money on having the 850 block modified and kick off with a 998 block.

 

The original 850 Con Rods are also in the same boat, but can be swapped for 998 or late Metro 850 Rods, they will be fine, though may need some small mods.

 

Pistons would be an issue, though you could look to alternatives from another engine (maybe some of the early bike pistons). I know that the early 850 blocks can't be bored too far and I don't know when (and if) this situation ever changed.

 

Sorry, what's the head you have?  A 12G125 is a little end bush.

 

Might be worth a phone call to these guys   http://www.mountune.com/   they used to do highly modified 850 engines years ago, but don't know if they still dabble in them, but it's only a phone call.

[Cooperman]

You will need a crank made from a billet of steel. Not cheap and certainly not something that is currently made as COTS, unlike the old Cooper 'S' crank where a billet steel one is available for around £1600 inc VAT.

One might guess than an 850 one could be cut for a bit over that figure.

The other issue will be rods & pistons. There is no way the original 850 pinch-bolt rods and split-skirt pistons would take high revs either, so special rods will be needed plus solid-skirt pistons, but whether they would be available is another matter.

To do less than this simply will not work as the engine will blow up at high revs.

An 850 could be persuaded to provide maybe 50 bhp with the original crank & a lot of work assuming that suitable rods & pistons can be found.

When the 997 and 998 were introduced the basis for better power really arrived, although the 997 was a bit 'iffy' as it was long stroke with pinch bolt small ends, but the crank was less liable to snap and it would take 6500 rpm.

Someone once described the 850 crank as being like a wire coat hangar  .

[Cooperman]

Not wishing to talk you out of this venture, but I do believe in going in to these sort of projects / ventures well armed with information (which is why you've posted here in the first place).

 

.

 

Sorry, what's the head you have?  A 12G125 is a little end bush.

 

Might be worth a phone call to these guys   http://www.mountune.com/   they used to do highly modified 850 engines years ago, but don't know if they still dabble in them, but it's only a phone call.

You sorta beat me to it.

[OzOAP]

Doing a mate an 850. Will put some pics up and report back when it comes off dyno.

[timmy850]

Is the engine the original matching numbers engine? I can see the appeal in keeping it, but by tuning it into a full face engine you'll be essentially writing off the block sooner or later as it will wear very quickly.

 

A 998 looks essentially the same externally, you can always keep the 850 engine to the side and put it back in. Swapping the engine back will take less than a day, and not require any holes to be drilled or modifications to the shell so you'll never notice it was swapped.

[Cooperman]

That is the best way to improve the power output, but surely the charm of an 850 is that it represents what a lot of people were driving around 50 years ago.

In the early 1960's modified 850 engines really didn't last very long. There were crank & piston failures, burnt out exhaust valves, cam journal issues (no cam bearings were fitted), and general wear. Even a good standard 850 didn't last much beyond around 40,000 to 50,000 miles before a 'Gold Seal' replacement was needed.

[mk1leg]

I rebuild an 850 engine back in the early 80s I rebored it to +60 and had the crank rods and pistons all rotary balanced new light fly and a stage 3 head with a 731 cam went like a bat out of hell....I had so much fun learning about rebuild engines with that old 850....