The other option I can see for the 15% explanation is that they originally experimented with pulleys by sourcing one from another supercharged car (or just another pulley off of something).
The overspinning the supercharger thing really doesn't do it for me because, while it's not a great setup, the 17% pulley doesn't seem to have too many negative sides, just a bit more heat and the potential for problems. If long term durability was a goal with the aftermarket pulley then a 14% pulley would be even more reliable with only a few less hp. I really hope he does chime in because a 15% pulley really does seem a little arbitrary for a standard.

 

I am curious if anyone has changed their JCW pulley to a 15% and what effects they have seen. I would love to see a comparison report similiar to this 15% vs 17% on this thread
https://www.northamericanmotoring.co...d.php?t=131093
Thanks, Steve

 

Note that the grand total difference between 15% and 17% was about what one would expect - 2.5HP, and at uselessly high RPM.

Hardly worth any potential decrease in SC reliability, IMHO...

 

But there is also a noticable improvement in the low end, which is what most people get the larger size for.

 

17% will def. net u more lw end tq...

 

I think if JCW is 10.98% is because they now thats the size the pulley has to be. the same way they decided they brakes has to be of X material, and the IC must be where it is.
I think they know what they do so if you don't want to hurt the SC the aftermarket pulley has to be in that size or you should change the rev limiter to at least 6800rpm.
it is important to know that even with the 15% pulley you are over the SC revs that the JCW pulley go (17340 for the 15%, 17149rpm for the JCW pulley size)

there is a lot of theories about 15% on SC with a lot of milles on it but what they does not say is how the SC is inside, how is the boost compared to the first day they install the pulley... I'm sure you can't remember if the car is pushing the same way as 30-40k miles ago.. again, if the JCW is 11% is for some reason and not an stupid or conservative one (is almost in the SC max revs, so I don't see that conservative)
and all of them are below the 100k milles, so I don't understand why some people said they 15% is the way to go.

 

Yep... I've talked to Eric about it as well... and his story of how they came up with 15% is pretty funny, if not exactly earth-shattering.

 

Get him to post the story here.

 

I'll try... no promises...

 

There is at least one person on NAM that has done 100k mile with a pulley, his name is suddenly escaping me, but he is here.

And FWIW according to your data the 15% pulley is only spinning the SC 1.1 percent faster than the JCW (which doesnt make sense really...)

 

Steve,
I changed my JCW pulley to a 16% S/C pulley along with a 2% Crank pulley and there is a big difference . Didn't get any dynos but big improvement in the low end and better spool up on the S/C, snapier response and extra boost. Should have done it ages ago.

 

I really want to know the reason behind the different pulley selection sizes. I have a theory, but will keep it to myself for now so as to prevent an argument.

 

The factory selected a pulley that allows the SC to spin up NEAR its full capacity. Just like it selected a tune that is NEAR full potential. From my understanding the reason the 15 is the perferred or most recommended is that it brings the SC up to its capacity at redline. More aggressive pulleys take it past capacity not adding any more up top but adding more sooner at the low end. The trade off for more boost at the low end is more heat up top.

So the factory backed down on the pulley, but also backed down on other things, remember they warranty the vehicle.

 

well the difference are the rpm's. for stock mcs is 6900 and jcw 7200, so those 300rpm are in play for the SC revs.
if you install the 11% pulley with the stock rev limiter then the SC will spin at 16584rpm. if all the numbers are ok (JCQ pulley size, crank pulley size) then the 11% can be used without worry about the long term use.

 

Of course, if the logic is that it is what it is because MINI has found that to be the optimum size -- the JCW would not need a reduction pulley because the standard "S" would already have the optimum size pulley.

 

Forge makes an 11.5% pulley

 

that is not what I mean. but in order with that.. then why the pulley is not 19% for the JCW? o 23%? if you think they just pick up a number and done.. well I think they are making cars and they now how to. and if they now that a 19% will give more power why they decided to use the 11%? we are talking about the JCW and GP cars, more power more cars on the street for mini.

 

OEM's just cant go and make a product that is designed to operate beyond another spec on the car....Thats the difference between an engineered and warrantied OEM product and the aftermarket. The aftermarket caters to those who will sacrifice reliability for max power and dont care if it makes the SC fail earlier.

Remember that before 05 the JCW upgrade replaced the SC completely, in 05 they put the coated blades on all as standard equip...The engineers who know vastly more about this car than any aftermarket supplier knew that there were issues at the high end with reducing the pully size

 

I've been running a 15% since 30k miles, and am currently just under 173,000 miles. So ~143,000 miles w/ the 15% and no problems.

Nik

 

At least that's what they always published.

 

Measuring one yourself will set you free.

 

+1 for measuring -- especially since we can't even agree on the "published" figures (others have said JCW has "published" 14.8%) . . . so I'll trust the numerous posted measurements.

luchini -- there is no question that BMW/MINI will always play it more conservative than individual modders. Saying that 11% is the optimum performance size because MINI picked it and they must know best, therefore, may ignore other factors (commonly known as "beancounters"). "Optimum" size depends on trade-offs each owner is willing to make between performance and reliability. I'm not saying the smaller, the better . . . as some have argued it may be that 19% reduction does not increase perfomance due to the increase in heat generated . . . all I'm saying is that just because BMW/MINI opted to only reduce 11% does not mean that they "know" that further reduction will not yield more power.

 

for what I have read here, and from people who measured the pulley, the JCW pulley is 10.94-10.98%.

xsmini, will be great to know the boost you are getting after more than 100k milles with the 15%.
anyway, remember Mini says the SC will keep boosting 100% between 100k milles. that does not mean the SC will stop working after 100k milles.
I read here about a SC with 15% replaced with a SC w/stock pulley and the guy said the new SC was making more boost than the one (used, don't know how many milles) with the 15% pulley. maybe is just too many milles on it, or maybe the pulley.

 

I had a 2003 with Quicksilver exhaust, Alta CAI and V2 15% pulley. The work was all professionally done by "well thought of" local shops. I sold the car and bought a used 2006 JCW (Nov 2006 build). It has the JCW engine, brakes, exhaust and intake. There is no comparison. The 2006 is SO much stronger everywhere in the rev range! I have a steep grade I drive every day at freeway speed and the JCW has more acceleration in 6th gear than the 2003 had in 4th gear. I was really amazed, actually. It seems that all the JCW stuff works together for a whole greater than the sum of the individual parts. This may not be comparing apples to apples, but there's more to it than just the 10.98745% pulley, I guess.

 

Interesting... but I think there are other differences between the 2003 and 2006 that may also contribute... gearing? Etc...

Now, in theory, the JCW car SHOULD perform better, with an upgraded head, injectors and ECU in addition to the pulley, exhaust and intake... though I suspect if you had a 15% pulley/intake/exhaust 2006 and compared it to a JCW 2003... might see different results...

But there should be little debate than a 2006 car with aftermarket 15% pulley, exhaust, intake, custom tune, head and injectors will blow the DOORS off a 2006 JCW car (e.g. RMW cars with 230+whp)...