Engine Drivetrain 1st Gen Cooper S Most liked posts in thread: 15% vs 17% Pulley

I went with a 15% on my JCW. The JCW pulley I took off measured to be 11.45%. To maximize any gains a re-tune is recommended, and more important the further you more away from the stock pulley.

Most consider the 15 to be more for track and the 17 more for street, so the use of the car is a factor to consider.

 

The 17 will generate more heat thus the reason the 15 is most widely suggested.

 

17 will give you help down low, but up high it'll spin faster than supercharger can handle, just generating a bunch of heat, but no improvement in power at higher RPMs. You're a track rat right? I'd stay with 15, it still helps down low, and is pretty much is the upper limit of what the supercharger can usefully handle at high RPM's. And it's not like there's going to be a huge difference in performance even down low going from 15 to 17, I don't think that small of a change is really going to be worth it, just my 2 cents.

I have the JCW, and eventually (when I'm having some other stuff done) probably swap out to a fifteen. Don't know why they didn't go with a fifteen in the first place....

 

JCW didn't come with a 15 as at redline thats out of the S/C range and being OEM and all....

 

Really? Even 15% is out of the S/C range at redline? Didn't know that, I thought 15 was the upper limits. Learn something new every day! Maybe I'll just stick with my JCW.

The other thing is belts--seems folks go through belts fairly quickly with the 17's.

 

Internet hearsay tells me the JCW pulley is an 10-12% reduction depending on which site you remember reading.

- Marc

 

Not true for the pulley I took off my 2006 JCW car. See post #3.

 

Yeah, everything I've read is the JCW pulley is just under 12 percent. There is a picture floating around somewhere of a JCW pulley side by side to a 15% pulley--the difference is definitely noticeable.

 

For my car, the 15% delivered 1.5psi of boost over the JCW pulley. While not huge, it still was significant and it made a real difference.

 

Before = 13.5 psi
After = 15.0 psi

I believe the 14 -to- 16 psi range is about normal for a 15% pulley and stock cam, head, headers. A high flow head especially, can lower the boost pressure a little.

 

Go with the 15% Jerry, or you could get one of those 16% ones and try to get Danny to install it . 15% will be perfect for what you do with the car.

 

So what are you waiting for? Get a decent 15% pulley, I like the Al ones with as many clamping machine screws as possible, three is too few for my taste, four is fine, mine has six. They are plenty cheaper than they used to be. Even for a JCW car, this is one of the best perf mods you can do. Street driveability increased significantly. Also, get the Napa/Gates 060535 belt, regardless of what Alta or some of the other vendors reccommend.......get the 060535 belt. It is a snug fit to get it on, but it will NOT slip.

 

No need to worry, I'm sure he will be going to MINICORSA so he will be in great hands :cornut:

 

Oh well yeah, if Danny is the surgeon then the procedure will be completed flawlessly and in record time. Great hands for sure.