Yes Howard they do add to it but in those hills having the 8.4's is a definite benefit over the UK Moke's drums.
We were at the back of the pack for a few of the runs and it was a lot of fun coming down the mountains/hills as we were all pretty much equal and it just goes to prove you do not have to have the fastest Mini/Moke to have fun.

All of the normally-aspirated competitors were affected by the altitude, so if you were faster than the others at lower altitudes, you would still be faster than the others at a higher altitude.

All of the engines would have less power and need longer time to accomplish the same workload compared to their own time at lower altitude.

Humans are affected similarly as internal combustion engines, This was a big issue for endurance events at the 1968 Mexico Olympics at 2240m altitude, the highest ever for any Summer Olympics. 

Thanks. I live at 6500 ft. Most places I go on a regular basis are downhill from here. MOTR Club drives can go up into the mountains, but that's fine - I usually take a faster mini, but it's not like folks are trying to lose you. Only been beaten by altitude one time so far. Turned back around 11,000 feet on Trail Ridge road a couple of seasons back. Didn't help that I had a full car (4 ppl) in a 998 and it was snowing.

Every so often I go for a drive with the new Mini club. Haven't had any issues keeping up. They may go fast on a straight, but slower than a classic MOTR ride on average!

Couple that Mal, with your 12" wheels vs the 10's run by Rob & Mark. It all adds up.

Not sure of what altitudes you will be encountering but i just got back from the CMU event in Tn and i believe the highest altitude we encountered was 4100 feet. I was driving a 998cc A + 3.1 fd Moke (around 1500lbs) and Rob and Mark were in two UK Mokes (around 1200 lbs) with 850 engines and 3.44 fd's.
They all handled the hills fine (obviously not the fastest but fine) but i noticed the 3.4 fd Mokes could pull away slightly on the hills with me catching them up on the flat sections.
I think as long as you do not get into some very seriously high altitudes you will be okay.

Thank you. The car I am looking at is very original, so putting a 1098 in would not be an option. I do have a 998 I drive quite happily w/o feeling need for more power, so it sounds like with a shorter final drive in an 850 I should be good - at least up to 60 mph or so on the freeway. But better to avoid the freeway when possible

Thank you - very helpful.

I don’t think you will have a problem. A powerful mini is always nice, but a slow mini teaches you to be a better driver. If you find you are really uncomfortable with the performance, keep in mind that a 1098 will look the same under the hood, but can move you along without fuss.

I have been on more than a few trips through there in both summer and winter in smog spec mini 1000s with 3.44:1 final drives. A good 850 with its shorter final drive would perform similarly.

As a young man maybe 16 years old I read my AH Sprite Bentley repair manual cover to cover. Now IIRC the adjustment wheel on the dizzy is to adjust the timing simply by turning the knob. As I recall this was to compensate for lower octane fuel should the correct grade not be available. The Bentley when with the Sprite when I sold it to buy a mini. Other wise I'd go back and reread that section. Steve (CTR)   

some simple physics applies to normally-aspirated engines as it does to mountaineers. Both feel the effects.

Both rely on atmospheric pressure to fill their cylinders (cars) or lungs (people)

with some rounding, an altitude of 6,000 ft drops atmospheric pressure by about 20%

Engine power is mainly limited by availability of oxygen, or more importantly, the pressure of the air that is always 21% oxygen at any altitude.

Fuel-injected engines use a mass air flow (MAF) sensor to measure the amount of air entering the engine, and injects the appropriate amount of fuel. A mini with a carb has no MAF, only  its variable venturi, carb piston spring, idle adjustment, and needle selection as adjustments. These cannot offset all the changes wrought by "thinner" air.

That leaves air alone as the main factor. You will have 20% less power, even if fueling is optimized.

The early 850's had a timing adjustment wheel for fine-tuning the timing. Wasn't its purpose to adjust timing for altitude, among other things.  IIRC one was supposed to retard the timing for altitude.

I have been driving classic minis since 1968. I have had some very quick/fast ones. For many years I autocrossed in a serious way. Engine spec was always over bored 1275 Cooper S, 13.3 to 1 CR, 3 into 1 header, 45 DCOE Weber, good brakes and 6x10 s with slicks. Running A/SP third North East, first south east and 5 at nationals twice. 

Wife and I decided to attend the Mini Meet in Denver. Having played with Webers I had and still have a very nice collection of calibration bits for a Weber. I ended up buying a soldering iron and using my jet drills to get a lean enough jet to get the engine to respond at that altitude. Over heating was also a real problem. Having lived with a 850 for three years of college I'm thinking you won't like it. Steve (CTR) 

More than a little disconcerting ....

Cheers, Ian

I've owned and driven an 850 quite happily at sea level.
I've never driven an 850 at altitude - what's it like to drive at a mile high, or higher?
How will town driving be?
How will freeway driving be - max speed?
How will merging onto my local 75mph speed limit freeway up a hill at 6,400 feet be?

Thanks in advance for your knowledge.