20% Supercharger pulley!!!

[LuckyRVA]

OK, I knew that would get your attention!

Since the 15% pulley still leaves the engine running rich, are there any smaller diameter pulleys in the works(20%-25%)? The pentigon engine seems like a stout little thing(particularly in the S's case), so is this a logical step to up the boost?



-Jason

[paulmon]

At redline a 20% pulley will be driving the supercharger past it's own RPM range.

Paul

[Casey]

i would have to double check the numbers again - can't remember off hand - but I believe a 20% pulley would keep the sc in its range at redline (maybe it was an 18% pulley) but once you change the software and raise the rev limit up you would then be exceeding the range of the sc)

[Jimbo_Mini]

I also seem to remember that there might be some issue with the diameter of the hub and the fasteners. There might not be enough meat left to go much smaller.

-Jim

[TonyB]

The water pump I believe becomes an issue then, or should at least me seriously considered b4 making such a move. It would be worth figuring-out about how much more power (hp & torque) one could expect. Given some of the unknowns, if less than 8 or so additional hp, I'd let the idea slide. I do know that one of the reasons I chose the Alta was that it would be easy to remove for such future potential move. Better incooling could be had quite nicely with the water to air that Randy has now...

[QQQ]

Randy from Mini-motorsport said some interesting things on this subject on MCO:

There are several reasons for the choice, all based on different aspects. Here are the main points:

Supercharger Redline
After discussions with several different engineers at several different manufacturers, the redline of the supercharger is in the neighbor hood of 17,200 RPM - depending on which one you talk with. More than 15% at a redline of 7200 RPM on the motor will put you right at that. Using 15% keeps it at roughly 17,100 RPM (again depending on who you talk with). This could be avoided by limiting the motor RPM, but because the horspower curve does not peak below redline, this would also limit your overall output.

Efficiency
It takes horsepower to make horsepower. What I mean by that is that there is a break-even point to where you are creating a lot of drag to make the boost. The more boost you are making using a supercharger gives more drag. Up to a point, the trade off is acceptable - you make 25 horsepower but it costs 10 to get the supercharger to push that much air, so the net gain is 15. Eventually, it will cost you more to make the power than you get back. This is only a minor reason not to go smaller, but it is part of the big picture. Heat can also fall into this category because of the way the air is moved. To make the boost, the Eaton creates quite a bit of heat - and the more boost is made, the more heat is generated. The heat reduces the density of the intake charge, and therefore costs power. This again is a balancing act - the boost makes power, but the heat caused by genereating the boost costs power. That is one of the reasons the intercooler is such an important option on this car - either cooling it externally (CO2 for instance) or making it more efficient.

Belt Life
When going smaller on the pulley diameter, you have more belt rap on the pulley. This may cause some belt interval issues, but I haven't seen that, and from the other guys I've talked with, they haven't either. It could be a significant enough reason though.

Water Pump
The water pump is driven by the supercharger, so if you reduce the pulley on the supercharger, you are spinning the water pump and the supercharger faster. Unless you change the angle of the blades in the water pump, at some point, the pump will be spinning fast enough to stall the blades - causing cavitation. This has yet to be an issue even at the 17% reduction some of the Euro guys are trying out.

The JCW pulley is 2.21 " in diameter, and the 15% reduction pulley is 2.17", so it is basically a wash - they use a pulley just like we do. The rotors are coated with graphite (not Teflon) instead of the epoxy coating on the S M45. The efficiency is very close to being the same on both types of coatings.

I hope that helps answer some of the questions - great question by the way.

Randy

[Liam"S"]

also another thing to consider is belt slipage they will do this on std pulleys allthough you can't hear it, it will slip its made to. and when reducing the pulley diameter greatly you are also reducing the surface area which the belt can grip on and so it will slip at the high end of the rev range so it has a negative effect. I am currently making ( yet another project ) a system to eliminate belt slip I am gonna give it a go on a std pulley and also a 15% reduced diamter pulley and compare boost readings. but goign silly small will just wears things out quickly.
your best bet is to just flow things in and out of the charger to get the air moving a bit more freely around the intake system first and like the others said concentrate on cooling the charge as well I am gonna get some intake temps later on today so I can let you know how efficant the IC is.

Liam

[jlm]

the only way to really tell is to try one out.
There was concern also that the 15% pulley would cavitate, over-re the blower, produce too much parasitc loss to be worth it, etc.

P&D made the 15%, a 10% and a few 20% pulley(s at customer special request) and all have worked fine. Physical size is a definite limit, but we did get to 20%. It is a bolt on to the same hub. no belt slippage problems, but a shorter belt is required (it should be used with the 15% anyway.)

As far as cavitation and over-revving the blower, my advice is to lower the redline by 5% (350rpm) when using the 20% pulley. The most useful gain you will get will be in the mid-range to redline where the motor will be running 99% of the time anyway, plus the extra 55 will bring on the boost that much sooner.

Liam's comments on flow and cooling are right on as anyone who has looked at the internal path will agree.

[LuckyRVA]

Thanks for your answers guys!

But, one more question...

Quote: Originally Posted by QQQ

Water Pump
The water pump is driven by the supercharger, so if you reduce the pulley on the supercharger, you are spinning the water pump and the supercharger faster. Unless you change the angle of the blades in the water pump, at some point, the pump will be spinning fast enough to stall the blades - causing cavitation. This has yet to be an issue even at the 17% reduction some of the Euro guys are trying out.

Is the supercharger ACTUALLY driven by the supercharger or is it just on the same belt?



-Jason

[QQQ]

Quote: Originally Posted by LuckyRVA

Thanks for your answers guys!

But, one more question...



Is the supercharger ACTUALLY driven by the supercharger or is it just on the same belt?



-Jason

Yep, waterpump is directly driven from the ss through reduction gears and by an internal drive shaft.

[LuckyRVA]

Ok, that makes more sense then. Thanks QQQ.


-Jason

[GordonD]

if water pump cavitation is the only/main worry why don't you just resize its pully to slow it down to factory specs.

[QQQ]

Quote: Originally Posted by GordonD

if water pump cavitation is the only/main worry why don't you just resize its pully to slow it down to factory specs.

As said the waterpump is not driven by a belt but by a driveshaft making use of reduction gears. I suppose the only way to reduce the speed of the waterpump would be to change the reduction gears

[QQQ]

Quote: Originally Posted by Max

Interesting John. I have used the stock belt with my 15% reduced dia pulley, with no problems. GGR (and others I think in UK) claim that a reduced length belt is not required. (although newminispares and a few other suppliers do sell a shorter belt)

Not sure if JCG use a shorter belt on the JCW S. Anyone know??

5,000 miles later no problems with the belt, but I will keep an eye on it (and an ear on it ) just in case....

regards

No other belt on mine either, still holds for more than 23,000 kms (approx. 14,300 miles)

[bigbaddaboom]

Not sure if it's a shorter belt on the JCW, they do change it though (well apparently... )