Upgraded Supercharger pulley/belt - How much more bhp?

[Rowj]

Hi guys

Just wondering how much more bhp you can expect from fitting an upgraded pulley and belt to a Cooper S? Thinking of a 17% reduction in pulley. Is it a substantial benefit to power output??? It seems to be a recognised way to increase bhp, but by how much?

Thanks Mark

[GreenV8S]

Rowj said:

Thinking of a 17% reduction in pulley. Is it a substantial benefit to power output???

A 17% reduction in the blower pulley increases the speed by 20% so you can expect to get up to 20% more power, other things being equal.

[Rowj]

And those otherthings are...?

[GreenV8S]

Rowj said:

And those other things are...?

You must stay with the speed range of the blower, the intake must be sufficiently freely flowing that the extra flow rate doesn't cause any significant extra pressure loss, your engine management system must be able to supply the corresponding extra fuel to maintain the optimum AFR, if the extra in-cylinder pressure takes the engine into detonating conditions you have to correct that (eg by cooler plugs, charge cooling, boost retard, boost enrichment, water injection, lowered compression ratio), the pistons and all the mechanical bits between them and the wheels must be physically strong enough to withstand the increased loads.

[Hartge210]

Alta claim their 17% pulley will give you an extra 20bhp, you should change the belt after approx 10,000 miles after getting it fitted though.

Check out this months Modern Mini magazine, the 'our cars' section has a write up on getting one fitted

[Rowj]

Thanks for all the feedback guys, much abliged!

I suppose the next question has to be - If you do change the belt and pulley and get an extra 20 bhp do any other components need to be changed in order to handle the extra power?

Cheers

[sjrainsford]

The engine has proved good over the years, and most respond well to a simple belt and pulley change.

Perhaps give Dave and Ade a ring at ThinkMini. They'll give you any advice you need.

[Loui]

I ran an 18% reduction pulley combo for a bit an found that even with a GRS intercooler it had a habit of pulling the timing an killing the power. I went to a 15% pulley an made 12 HP @ the floor as it stopped pulling the intake temps.

The other thing is with a 17% pulley an a stock intercooler if your sat in traffic for a while then boot it straight after you could potential blow the thing to bits due to heat.

Just my 2cent

[Silent1]

FYI, the max speed for the supercharger is 16,000 RPM which means you can only go to a 10% smaller pulley (the size used in the JCW kit)

If you really want i'll dig out my graph with all the calculations on, but TBH they're meaningless as despite all of it i went with a newer teflon coated 'charger, 440cc injectors, 17% pulley, alta CAI, colder plugs, janspeed manifold & catback, the list goes on.

[RKDE]

the JCW is 11% though...

[Silent1]

RKDE said:

the JCW is 11% though...

You could be right, IIRC the difference is something along the lines of 10.4%/11.4%

[RKDE]

Since I have both items in the garage I should go out an measure them to confirm this...

[softtop]

RKDE said:

Since I have both items in the garage I should go out an measure them to confirm this...

Not if you have got lost but the last time you were seen you were heading off to the garage with a tape measure in your hand