Ian Cull has a review for us on upgrade kit for prior JCW MCS's. This kit brings the total power from 200 to 207-210 depending on how you measure it.

Today I took GBMINI to MINI of Peabody to have the '05 JCW “step-up”
added; GBMINI was upgraded to the original JCW spec back in January and the
difference was very noticeable. Since then both I and other drivers have
commented on how “smooth” JCW upgraded cars perform, in comparison to
aftermarket upgrades.

In September GBMINI performed well on the dyno but was beaten in raw figures by a couple of aftermarket upgraded cars.

A common theme of aftermarket upgrades is to replace the air intake with
one that allows better air flow into the supercharger (and so into the
engine) – now the JCW kit offers the same type of air intake improvement
but in keeping with the “smooth” (and more expensive) package, their
system is more sophisticated than other options on the market.
The new JCW air intake has the original front air intake but has an
additional rear intake which draws air through the duct at the base of
the windshield; there is no cutting of panelling – a new pre-cut panel
comes with the kit. There is also an electronic valve which only opens
to allow air flow through the rear duct at 4500 rpm and higher; an
update to the engine computer and a small wiring harness controls this.

The result is that you do not get the extra loud noise associated with
many aftermarket air intakes – at least not during normal driving below
4500 rpms. But when you push, the valve opens and the noise level
increases noticeably as (presumably) air flow increases and extra
horsepower becomes available. If you push to red line before shifting, the valve will remain open as
you continue accelerating through the gears, keeping maximum air flow

To make better use of the extra air, the '05 JCW kit also replaces the
fuel injectors with “bigger” ones that presumably allow a higher maximum
fuel flow into the engine – I don't yet know if this will affect mpg,
but I guess that during normal driving there is little if any

New dyno run shows just completed this weekend show a consistent 5-8hp gain from about 3000rpm to red
line. For an unknown reason (V39 software? Dyno operator error?) red
line is about 200rpm lower than previously so the maximum gain is only
4hp. But the improvement all through the range (also coupled to a nearly
10lb-ft maximum torque gain at 3500rpm) gives confirmation of general
“butt dyno” opinion that the upgrade is beneficial.

Again we see on the dyno that a well modded aftermarket MINI beats the
JCW for raw maximum hp (getting about 197hp against 193hp) – but a
comparison through the rev range shows that the JCW offers more
performance lower in the range, at “normal driving” rpms – again this
helps to confirm general opinion that the JCW is a “nicer” package.
Is the JCW worth nearly $6000 compared with perhaps only $2000 for a
good Randy Webb package? Opinions vary here!

A couple more links of interest:
Weblog entry for yesterday including the dyno run details:

A before (September) & after (yesterday) dyno plot of the JCW and JCW+

You can see Ian's full gallery here.

Ian Cull's Rating: 4/5

A big thanks to Ian for sending us this review. It would be interesting to hear opinions from other's who own the upgrade kit. Ian's rating, while good, wasn't as high as it would have been due to the cost vs the dyno results.

While I haven't drive the car, my conclusions based on everything else lead me to believe that it's frankly hard to compare JCW upgrades to the rest of the aftermarket world. With JCW you have (A) performance (B) refinement (C) warranty (D) actual added value as opposed to losing value when you go the aftermarket route. Because of that it's difficult for me to really rate it based soley on performance for the money. However if you brush all the other factors aside and just look at performance and price Ian's rating will probably make sense to many out there.