Ok so I've got a mini cooper with the JCW kit fitted, can somebody please tell me what these reduced pulleys are all about?
Whats the difference between the cooper S, and JCW supercharger, what size pulleys do these have as standard, and what sort of increase in BHP should i expect from a standard 200bhp JCW mini from replacing pulley to a 15% or a 17%
Don't know the Bhp changes, it really depends on your engine and the actual power you have... the JCW pulley is about 11% reduced over the stock S also the pre face lift does not have teflon coated rotors on the stock s but the jcw always has Teflon coated
Though my JCW has 193.5Bhp and mine is the 210 version
For everyday power increased id put a GRS intercooler and 17% pulley on there You'll feel a nice difference around town and when you really put your food down.
With the right ecu tune, the gain on 15-17% reduced pulley will be greater than 4 HP over the 10.5% (that's not a typo) JCW pulley. I have seen it myself during dyno tuning sessions. Many JCW owners switched to 15% up and were very happy on how much it changed.
someone has done some monitoring of supercharger boost/inlet temps, i need to find the link, i think they worked out that 16% reduction gives you the best most consistent performance gain throughout the rev range, with a higher %, heat becomes too sig a factor at the top end, any less % and you loose a little low down torque. don't know if these figures are def accurate.
personally, i'd want to preserve the longevity of my supercharger. i'm not sure what the tolerances of the eaton are supposed to be.....i've got a 17% on my car at the moment, i am thinking about changing to a 15% and combining it with a W2A grs IC. that should give good boost all the time and hopefully?? stay within the tolerances of my supercharger too.
i find on my daily commute, my GRS a2a gets heat soaked and doesn't work that well, though it's much better than the GP IC.
if you've already got a jcw 10.5% / 11.5% pulley, presumably if you're a jcw you've got the 380cc injectors and gp intercooler? best thing you could do is either just get an ecu remap or add a Big Valve Head, aftermarket exhaust system and get a remap. a further reduction to your pulley may not add that much more....and i think the jcw pulleys are a bummer to take off aren't they? so you'd need to buy a supercharger and pay for removing old supercharger and fitting a new one with new pulley. with that money, you could get a tune.
I read somewhere (MC2 magizine, perhaps?), that a 15% reduction would bring the the eaton to its maximum rated RPM at redline, this is something that I considered before I bought mine. I'm not 100% sure but I think that sounds like an appropriate safety factor for mini to build into the design.
Mods:
MiniMania CAI and 15% pulley, Racing Brake front rotors, EBC Green Stuff front pads, ALTA 19mm anti-roll bar
17% works great but if you live your life above 6K rpm then maybe isnt for you. Dont believe everything you read.....
So if you want a higher torque curve then 17% is best to go for and if you want HP pub talk 15% is better The SC only starts to build real heat from 6,000rpm onward to red line.
I live in miami florida and as you know the weather here is really hot. Will a 17% reduction pulley work in this weather?? I use my car to drive to work and for rides in the weekends and of course i step on the gas a few times on the road and go on trips of 2 to 4 hours at 70-100mph speed. do you think heat could be a factor do that this pulley ma also creat more heat do to the mor compresion. what do you recomend? my mecanic says it will not work corectly and that my checkengine light will turn on and if accelerating a lot it will turn the ecu into a safe mode and restrict the gas.
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You'll feel a nice difference around town and when you really put your food down. 
