22 replies to this topic

[MiniShane93]

Hi all,
I have recently brought a 1980 Austin mini 850, i love it but its a bit "slow"
Does anyone have any simple and cheap tuning ideas?????

Thanks

[Cooperman]

The 850 is probably the easiest Mini from which to get more power as the engine breathing is so bad to begin with.
Start with a better head, either by gas-flowing the one that's fitted and putting in bigger valves, or by finding a 998 Cooper head and skimming it to get the compression ratio correct at about 9.3:1 maximum. Don't go much higher as the pistons are not as good as 998 ones.
Then get an HS4 carb to replace the HS2 and a better inlet and exhaust manifold. An original Cooper 998 exhaust system is good to do.
You can change the cam on the 850 without removing the engine and the Kent 256 is good for an 850.
Just don't go revving it too hard as the crankshaft rev limit is only about 6500 maximum with a sustained 6000 maybe pushing your luck a bit.
A sensibly modified 850 can give around 44 bhp with reliability which at 10 bhp increase is really good.
I hope this helps

Edited by Cooperman, 03 January 2011 - 12:31 AM.

[jamiestevenbell]

i have a mini 850 and i have fitted a stage one kit and a hs4 carb and an electronic ignition kit and it has 38bhp it dont sound alot but its amazing how much more driveable it is if you drive it properly but you cant go wrong with the previous info given

[danrock101]

I've got a 850 too and it's a ball ache lol, getting overtaken by old women in their ford KAs on a sunday morning! bloody good job the tax is free and the fuel consumtion isn't too bad... would love to tune it really but don't want to spend much on it but if I keep it I will do something along the lines of what cooperman recomended, I'll probably just get a standard head 998 head with unleaded seats and port it myself for cheapness.

[mk1leg]

In the early 80s I reworked an 850....I had taken the bore out to cooper S spec and reground the crank ni-tempered and tuffridded it, new rods, new 731 cam, stage 3 head (biggest I could find), light fly and backplate, orange clutch plate, 40dcoe webber, uprated g/boxwith a 3.765 diff, maniflow LCB and exhaust, and would you believe I did all this for £500...............OH those were the days when parts were cheap.......NOW when you mention the word Mini everythings doubled............

[minidave_69]

I had an 850 a few years back... not the fastest in the world all I had fitted was a different carb, can't remember what one it was now & a full maniflow exhaust system on her, had her rolling roaded & she flew
Easily out did this young tit in a thou that was in the my mini club at the time

[Cooperman]

The limitation with the 850 is the crankshaft. Sure the split-skirt pistons were not too strong, but solid-skirt ones cured that. The standard crankshaft, even balanced, really is limited to around 6500 rpm. In the 60's it was possible to get a competition crank which was good for 7500 rpm and I have heard of bored out 850's, +0.060", with flat top pistons, big-valve head, comp crank, etc, etc, giving around 80 bhp at 7000 rpm with a full-race cam. That wouldn't last long, but what a performance from 850 cc. Those cranks are impossible to find now.
One other thing to remember is that on the 850 the cam ran directly in the block with no cam bearings. In order to get reliability with a modded 850, proper cam bearings must be fitted, which means line-boring the block.

[luigi86]

if you want to get serious, you need to get the block to accept two cam bearings otherwise your just going to blow it up.

Im planning a very highly strung 850, but It costs a bomb and its almost impossible to find parts so I may just go down the 998 route.

The same theory applies for every a series.

Better fueling, better breathing, different camshaft, different compression ratio and off you go.

you can make them reasonable but its always going to feel slugish, some people love that though. Most dont which is why so many people threw there 850's away and now parts are like hens teeth!

[project mini chris]

12g295 998 cooper heads will go straight onto your 850. Then maybe a stage 1 kit, Electronic ignition, modified camshaft?, maybe even a hs4 or twin SU carbs?

Edited by project mini chris, 03 January 2011 - 03:29 PM.

[Cooper-202S]

Has anyone come across any solid skirt 850 pistons recently, all I've seen are a few split skirt set and Hepolite W cast sets on Ebay.

[Cooperman]

12g295 998 cooper heads will go straight onto your 850. Then maybe a stage 1 kit, Electronic ignition, modified camshaft?, maybe even a hs4 or twin SU carbs?

Not quite straight on as they need quite a bit skimmed off to get the C.R. correct (like about 0.090"), but, yes, they do just bolt on and are a very good modification once skimmed correctly. It is important to get the C.R. to just over 9:1 if still running split-skirt pistons.
If only the competition cranks were still around. Not seen one in years. I got my first 850 48 years ago this April. At the time it felt quite quick with an improved head, better valve springs and a richer carb needle! Those were the days - single leading shoe drum brakes and 145/80 x 10 Michelin 'X' radial ply tyres.
For the road, around 45 bhp can still be reliable and then the 850 goes very well, especially as the early ones were quite light in weight and didn't have as much drag from things like wheel arch extensions, wide tyres and huge wing mirrors. In fact, wing mirrors were not standard and my Minis didn't have any back then. Dear little cars!

[MiniShane93]

cheers for all your help, sounds like I can do alot to it.

[Authi]

 

Take a look at this video, 850 Mini, 12G295 head and Injection (Canems ECU with MPI parts) ,  rest of the engine untouched (And profesional driver....)

Edited by Authi, 03 November 2018 - 10:01 AM.

[Retroman]

The limitation with the 850 is the crankshaft. Sure the split-skirt pistons were not too strong, but solid-skirt ones cured that. The standard crankshaft, even balanced, really is limited to around 6500 rpm. In the 60's it was possible to get a competition crank which was good for 7500 rpm

 

 

   Surely the modern 848 will be stronger, the last few I have seen are EN16T, and with the bearing overlap more than a 998 ?

 

Someone may know were all the A plus 848's an EN16T crank ?

 

I would be using 998 pistons which gives you a good choice and more cc's too...998 + 0.080 will be about 950cc

 

The max at 68mm bore you would have a short stroke 996, which would not be torquey but fairly revvy 

 

the 848 the crank being the same stroke as the 1071 S

[Minigman]

The innocenti mk3 850 had 47bhp as standard fitted with a 12G295 head. No idea what the rest of the spec is but that was from early 70s.