Bottom end on Cooper S's?
 

How stout are they? I'm assuming they are more so than the NA versions? How much boost can be ran reliably and what's the max boost the stock blower can output efficiently (without heat issues). What will the stock fuel system support?

Same question for the tranny - either the manual or auto - how much power can it hold?

I have a 2007 MCS with auto. The low end is pretty good since the car is at full torque from 1750rpm

Not sure about modding.

The bottom end is very strong from the factory (same for R53 and N/A) Before my track car became what it is, I had it twin-charged and was running 22lbs w/ the stock internals. Stock supercharger can efficiently push about 17lbs with a 17% reduction pulley, though I would not recommend this for the track because you WILL over-rev the supercharger at higher rpms.

Injectors don't need to be upgraded until you're trying to push it past about 220whp. To even get past there, you'd have to be looking at ported/polished head, aggressive cam, forged pistons, equal -length primay header (all available from Revolution Mini Works)

I don't have any experience with the cvt trans, but have heard that its prone to fail rather often in stock trim, so if thats what you're working with I wouldn't push it too far because they are expensive to replace.

Hope this helps a bit:D

+1 on the bottom end of a MINI being tough. many applications of over 250 whp w/ stock bottom end. some over 300 w/ twin-charge or turbo applications. if i were thinking of doing anything w/ the bottom end, i would wait for RMW's 2.0l stroker kit! 240+ lb-ft of torque! that will be fun.

i realize i'm over a year late to this party, but a stock CVT cooper pushes 115 horsepower and 110 lb-ft to the wheels. the CVT can only support up to 150-ish whp and 120-ish wtq, according to ZF, the manufacturer. anything more, and you're liable to have the metal belt at the heart of the CVT explode.

tuning potential? i think not.

it's an awesome transmission for the day-to-day (i would know, my mini has one) but it has zero tuning potential whatsoever.