I think you will find that even supercharged / turbo charged engines will suffer the same power loss as a normally aspirated engine, because it is the level of oxygen in the air that is different at higher altitiudes so even if you can get more air into the cylinders it will still have less oxygen due to the altitiude. The combustion process needs the oxygen to provide a good, powerful burn and lack of it will give a reduction in power.

Have to disagree with you there, as i'm pretty sure that in the troposhere the composition of air does not change significantly with altitude, i.e it is pretty much 21% Oxygen & 78% Nitrogen (plus some other bits & bobs)

The only reason their appears to be less oxygen at altitude is because the air is less dense, due to the fact that the air pressure decreases as altitude increases.
From the equation PV = mRT, assuming you keep the volume the same (i.e your engine capacity doesnt increase with altitude...) as you reduce the pressure the m term in the equation (which equates to the mass of the air/oxygen) has to go down to balance the equation.
If, at altitude, you increase the pressure (for example, using a turbo) to the same as what it would be at sea level (as an example) then the engine will produce the same power as it would at sea level. The only difference is that the turbo / supercharger has to work harder at altitude to achieve the same pressure.....
Blimey that went on, sorry. Hope that clears things up.

Well, thats all a bit technical for me! What i based my idea on was that the vehicles i work on suffer from power reductions at higher altitudes. Working things out from your theory this is probably due to them having purely mechanical turbochargers with no variable wastegates, or variable geometery turbine etc. This would mean that the engine electronics are unable to influence the amount of extra air that is needed for the combustion process. Thanks for your input mate, it was very educational!

Our Harry does know his stuff.

Exactly. Generally i would expect most older turbo / supercharged cars to suffer the same as N/A cars, as they would only have mechanical wastegates. Some new cars would have MAP (manifold absolute pressure) sensors controlling the boost pressure, so would give the same performance whatever the ambient pressure.

I have had my ST now for 5 days!! and still getting used to the stripes!... last year I owned a cooper S so can compare both. The Cooper S was a great car, and seemed a lot quicker in normal driving around town than the ST feels currently. But, the ST feels more grown-up for some reason ;-) not sure why, but it's nice to have a bit more space to play with... I loved the Mini and currently love the ST... in many ways very different... but both are great cars and anyone wanting to choose between the 2 would need to drive them both... oh and the small matter of the 3 grand difference in cost between my 2 cars plays a part ;-)...

Ive decided against the ST as you may have already read (wasn't blown away by performance) but tonight I was driving my parents S and had an ST come up along side me

Anyway I really had to thrash the Cooper S to get away, not sure if this guy's ST was modded or something, but boy did that thing give me a run for my money (on my private runway ofcourse)

It certainly kept up, only just got away.....

2nd Verdict on the ST, maybe it's quicker than I think even after a test drive!!!

i have driven with a Cooper S convertable a couple of times and the lady driver pushes it......managed to stay in touch everytime so far! the little is quick if you work her....

Drove a mini cooper s at a track day, I dunno if it was the fact that i was on a track but the car didnt impress on power. The worrying thing is I was driving a 1.4 mk6 at the time. Plus the seats are rubbish!