Tuning a 850 engine

[rickmk1]

HI all.

In my plans to restore my MK1 850 Super, I would like to get some more HP form the engine but keeping it as original as possible and keeping it as is, 850cc. I don't want a hot engine, only 6-8 more HP if possible. I am thinking the following mods:

Electronic ignition and high power coil
Bigger carb, like a HS4, may be better than twin carbs for this capacity??
Stage 1 kit complete
New camshaft (256 could be or 266 is also ok?)
Increased compression up to 10:1 by skimming the head
Head ports improved and gas flowed
Lightened flywheel (but wich is the ideal weight)

What do you think?

I have also seen that there are rockers with different ratios 1.3, 1.5, 1.7 and I have seen in the Minisport website that the can do the same effect than a fast road camshaft. Is it real. In this case, wich one shoud be better adn are the good for 850 engines? It could be a good solution because I have been told that fitting a fast road camshaft in this engine requires to rebore the camshaft seats to fit rods (I don't kow if these are the corerct words in english, so sorry if there are errors).

How much do I need to skim the head to get the 10:1 compression ratio?

Thank you very much for your help.

Regards from Spain.

[gs.davies]

I was going to do just this until I discovered the costs of the 850 pistons. Once coupled with the costs of getting some cam bearings fitted I decided against the idea. That said, here's what I'd planned

+40 (bores were fine as was but all four pistons were showing signs of stress cracking around the gudgeon pin)
12G295 or 12G202 head, skimmed to increased the CR to around 9.5:1
Cooper 997 spec camshaft
Twin HS2 and Cooper Airbox
Crowsfoot exhaust manifold into a single box RC40
A suitable distributor curve.

I'm now doing the same build but on a 1098 which I'll mate up to the wand change box. Apart from the twin carbs and manifold it'll look very 850 under the bonnet. I'm not going for a servo (yet) I'll see how I get along with single leading shoe brakes and a pair of non spacered Minifins...

[timmy201]

In the yellow Vizard book he goes from 20hp at the wheels to 25hp with essentially a "Stage one kit" (exhaust / inlet manifold, full RC40, KN filter, spark plugs). A "high compression 9.4:1" head raises it again to 31hp. It doesn't mention changing the cam as it is the "bolt on" chapter.

There are some 850 pistons here, can't see them in stock at the usual UK suspects.
http://minisport.com.au/pistonsa-rings-liner-sets

[1071 S]

Get one of Clive Trickey's books on tuning the 850 - the original Mini tuner....( at least one who wrote about it

Cheers, Ian

[mk1]

If you do a search using the search button in the top right hand corner of your screen, you will find a lot of very good info on tuning 850s.

In a nut shell, it can be done & you can get a reliable mildly tuned engine out of an 850. If you want more than about 45 bhp then it will start to get expensive & unreliable.

[rickmk1]

Thanks all for your comments.

I will start my search. I don't really want more than 7HP, just enohugh to have a happier engine.

[ivor badger 2]

Warning. If it's a 60s 850 engine, it only has one camshaft bearing and when run hard, the cam wears through the block. OOPs!