Turbocharging Vs Supercharging

Turbos are mini turbines spun from exhaust pressure leaving the engine. At lower engine rpms, there is less exhaust created, which does not create enough pressure to spin the turbine fast enough to spin the second part of the turbine that creates boost pressure. Low boost pressure means the motor is effectively naturally aspirated. Turbo lag is the wait time for there to be enough exhaust pressure to spin the turbine fast enough to create enough boost to create a noticable gain in performance.

With turbos, larger is not always better, with a properly sized turbo, it is said that you can virtually eliminate turbo lag.

Superchargers spin off the motor, so they are not as efficient as turbos (they use the motor's energy versus the motor's exhaust (spent energy)). However they are constantly spinning when the motor spins and are much more effective over the entire rpm range.

I won't speculate which will be better, the supercharged mini or the turbo charged one, although I am quite happy with my supercharged mini.

turbo more expensive

im pretty sure that a turbo setup is more complicated. a supercharger just mounts directly onto the intake manifold and attaches to the pulleys via a belt. for a turbocharger, you need more piping, more intercooloer tubing, you gotta worry about keeping the air and oil more cool since it runs off exhaust gases which tend to be hot. Also the amount of boost it pushes relies on software. it just doest seem that much cheaper to me.... maybe theyre less prone to breaking? either way there are ups and downs. downs are that with turbos yes, you do get turbo lag. buuut you can easily increase horsepower by just messin with your ecu and boost controller. also you get to have a blow off valve which is super cool. you pretty much dont have to add any parts if you wantmore hp. with the super, you gotta get a pulley and new software.

I think the reason they switched was because nowadays turbos are more conventional. They are used far more in the auto industry than superchargers, which leads to cheaper parts, and bigger workforce that is familiar with tubros.
my 2 cents

My current car is a Mk4 Golf 1.8 turbo. Come March though, my Cooper S arrives WOOHOOO!!

The Golf is chipped to 200hp, so its very quick, quicker than a CooperS! There is turbo lag, but its hardly a problem at all, you gotta be below 1900rpm to even feel it. Above that the turbo spools up very quickly. Even the spool up is nice as you can feel the power picking up and shoving you back. Turbo is also fairly quiet but it whines similarly to the supercharger when its boosting hard.
Rarely notice the turbo in anything but first gear, beyond that its just got masses of mid range grunt, and its fairly fuel efficient to boot (yawn!)

The lack of lag on the Golf's engine is due to the size of the turbo. Its quite small and lightweight which means it can spin up very quickly, idea being it drives like a larger capacity car to joe public without the problems of turbo lag. Smaller turbos boost quickly but can't move much air so they have less top end. A big turbo will take an eternity to spin up but it'll generate some serious bhp once its going!!

I found the Cooper S to be very similar to drive to be honest. The supercharger effectively mimics the small turbo in the Golf. Obviously there's a complete lack of lag, but both engines feel similarly linear and responsive. Main difference is though, the Golf's torque arrives a lot lower down.
I'd say that turbo charging if done correctly is the better approach. Its definately cheaper and if done wrongly is nasty, but if done well, like with VW's 1.8T engine, its fantastic. Apparently their new 2.0T is even better.
That saying, I've still traded the Golf in for a Cooper S.. COME ON MARCH!!!

Bah. I'm not a big supercharger fan... They tend to run out of steam up top. Superchargers are for hillbillies with 5.0L engines that tickover like a steam engine.

I've been tempted in the past to rebuild an S engine with turbocharging instead of stuporcharging... Guess the big boys finally beat me to it. As for the whole lag issue, I actually PREFER a little lag. If you are driving at 2000rpm, do you really NEED power? If you are making any attempt at being quick, then you have no business in that end of the rpm range. I find that having a rather docile engine at low rpm is nice around the city. Get the car into the powerband and it becomes a totally different creature. This dual personality adds to the versatility of the engine imo.

Again just my opinions. The supercharger was the main reason I stayed away from the MCS model. Had it been an MCT, I would have bought it in a heartbeat. As it is, I'm pretty happy with my MC as a friendly commuter compliment (that can still rail the corners) to my more brutal toys.