What are the differences between a 15, 16, 17 & 19% pulley..?

Originally Posted by Reedy

Right following on from Pulleys as i now have a better understanding
Thanks everyone

What does a upgraded crank pulley do..?
Same as a reduced sized s/c pulley, but by the opposite way in being larger

I have seen 2% crank pulleys is there any other types..??
3% iirc


If you have a 15% supercharger pulley and you add a 2% crank pulley does that mean you get the performance of a 17% supercharger pulley..??

yes

What BHP differences would you see on a 15% and 17% back to back?

[Jaw_F430]

Originally Posted by George

What BHP differences would you see on a 15% and 17% back to back?

I don't think there would be a massive difference TBH. Maybe Paul could chime in with some figures

[Reedy]

Ok so if a 15% supercharger pulley and 2% crank pulley give the performance of a 17% supercharger pulley....why bother with a crank pulley and not just go and fit a 17% pulley..?

Because some people fit a 15% first then want to increase, or do what alex did and add a 3% to his JCW pulley that the car came with to make 14%ish

Jaw, maybe theres no difference in total BHP figure, but I'm pretty sure there will be more low down hp/torque

[Reedy]

Originally Posted by George

Because some people fit a 15% first then want to increase, or do what alex did and add a 3% to his JCW pulley that the car came with to make 14%ish

Jaw, maybe theres no difference in total BHP figure, but I'm pretty sure there will be more low down hp/torque

ok but why not just change the pulley to a 17%..??

[Jaw_F430]

Originally Posted by George

Because some people fit a 15% first then want to increase, or do what alex did and add a 3% to his JCW pulley that the car came with to make 14%ish

Jaw, maybe theres no difference in total BHP figure, but I'm pretty sure there will be more low down hp/torque

Yes it moves the power in the rev range

[citro]

Originally Posted by Reedy

Ok so if a 15% supercharger pulley and 2% crank pulley give the performance of a 17% supercharger pulley....why bother with a crank pulley and not just go and fit a 17% pulley..?

I've got the 15% S/C pulley and the 2% Crank pulley combo, and from what I've read, it is quite identical to having a 17% S/C pulley, with the advantage of losing some weight on the crank which, theoretically speaking, makes the car "looser", revving faster.

[R53mcs]

15 +2 = 17 .... its not quite that simple!

Yes basically the theory is if you fit X supercharger pulley, and then add Y crank you get more boost though ... You can kind of expect a 15+2 to make around the same power as 17 ... not far off anyhow. There are concerns expressed on cranks, but in my eyes some of this is people who just dont know worrying unduly, some is scarmongering, and as yet knowone really knows. I have yet to have anyone actually show me a cranked car thats had a failure that can be tracked directly to the crank pulley, as the same fault has been seen on non cranked cars!

[MINI-Morgan]

A few questions you need to ask too:

1) is +2% the eqivalant of 2% on the SC or 2% increase in crank size. On the SC this will be much much more than 2%

2) Think of gear ratios..... now whats easier for the engine to turn. 15% SC and +2% Crank or 17% SC pulley. Anyone done the test?

[R53mcs]

The other bonus of oversized cranks, if there is any is that as its a 2% increase over stock this means the contact area is larger with the belt. A common issue with 17 and more reduced pulleys is tendency for belt stretch and slip, as the contact area for the belt is reduced. If you fit a 15-17 reduction scharge pulley and an oversize crank you gain some of this contact area back thus giving the added bonus of a slightly reduced risk of slip, and maybe a reduced risk of stretch but with increased boost?!