General Centrifugal ?: Clutch to slow SC revs at higher RPMs

I'm sure something like this could be possible; however, I'm not sure if could ever be cost-effective. Basically, I was wondering if anyone has ever thought of coming up with a SC pulley design that would allow the pulley to begin to disengage as the revs got to a certain RPM. This would allow the supercharger to get to its maximum efficiency quickly and then gradually disengage to keep the supercharger at the RPM where it is most effecient. The Mercedes Roots blower has a magnetic clutch that disengages the supercharger below 3k RPMs to enhance fuel mileage. I was wondering if something like this could be retrofitted to work in the opposite fashion. Also, I'm not sure if these clutch devices are "on or off" or if they can gradually disengage.

Let me know your thoughts...

It is On-Off and someplace I still have pictures of the unit I built 8 years ago using a air condition clutch as the design. I was using it on a V6 car which allowed me to put the crank pulley 4" farther out because of the mag-clutch was so far forward. The design worked but then your dragging a 40-50hp draining device and the car was so sluggish going past the impeller so I designed a air bypass that used a vacuum switch that routed incoming air past the supercharger which worked great. I used this on my 88 Cougar for in the winter to limited power, I decided it is not worth the hassle and just use a remote wastegate and limited your boost number or get a electronic wastegate and program your curve and limits.

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Originally Posted by speedytang

It is On-Off and someplace I still have pictures of the unit I built 8 years ago using a air condition clutch as the design. I was using it on a V6 car which allowed me to put the crank pulley 4" farther out because of the mag-clutch was so far forward. The design worked but then your dragging a 40-50hp draining device and the car was so sluggish going past the impeller so I designed a air bypass that used a vacuum switch that routed incoming air past the supercharger which worked great. I used this on my 88 Cougar for in the winter to limited power, I decided it is not worth the hassle and just use a remote wastegate and limited your boost number or get a electronic wastegate and program your curve and limits.

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Speedy,

I figured you had thought of/tried something similar. It certainly would be cool if somehow the idea could work. Centrifugal superchargers would rule the world!

:D

It works but it is cheaper and less junk under the hood to use a wastegate from a turbo car.

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Originally Posted by speedytang

It works but it is cheaper and less junk under the hood to use a wastegate from a turbo car.

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Hmm. I don't know if we're on the same page. I don't want to let air out. I was thinking of using a fairly small pulley to reach maximum flow by say 3500 RPMs then keep the supercharger spinning at that same speed (creating the same efficient flow) all the way to 8000 RPMs. In my application, I ended up choosing a pulley which will limit my revs to 7k RPMs in an effort to make better low-end power; however, if a device such as I'm trying to describe existed, I could have "full boost" early on in the powerband and keep that boost throughout the powerband. Are we on the same page or am I missing something?

I understand what you are saying but since that can't be done because a slipping clutch design would not last but seconds just like a car clutch slipping all the time I was just giving you a way to control your boost at all rpms so that with a small pulley you could have 8psi at 2500 rpm and at 7500 rpm without the blower climbing with engine rpm. Now if your running a V-Belt you could put a manual tensioner with a cable to control how tight your belt is for slippage...!!!! Maybe....LOL

Speedy:
doesn't a wastegate allow exhaust gas to bypass the turbine to limit boost? Not much use on a centrifugal blower! <grin> You were probably thinking of a blowoff valve -- BOVs are for unmetered air systems only, i.e. alpha-n or MAP; if you blowoff metered air, the engine will run pig rich.

Pianoman:
There are two methods I can think of to limit boost on a centrifugal, first one is an intake restrictor after the blower, i.e. take a page from the Nascar book to limit HP. The only problem I see with this method is that the air temps will keep climbing with rpms as air stacks up behind the restrictor. You could install the resitrictor before the blower, or even run a small throttle body before the blower, which would improve efficiency at part throttle -- no need for a blower bypass system if the blower is seeing vacuum on the inlet side.

2nd thing I thought of, much more crude, was some kind of cockpit adjustable belt tensioner similar to cockpit adjustable wastegate knob. If you are running a smallish blower pulley, you could adjust belt tension so that it starts to slipping at 6 psi or so - blower load is a function of backpressure, so it should build up to your preset boost limit quickly, and then start slipping progressively worse as rpms climb. Of course, this method will accelerate belt wear, and might not be very repeatable, but I'm sure it would work as a crude crutch, probably 3/4 of the questions on this forum dealing with a low boost problems are due to loose belts!!!

Yes that is what I was saying...LOL
I am working on a Turbo car at this time and it all starts to run together. I still think a Electronic BOV(lol) would be the best choice but then your working a compressor at full blast early making a lot of heat.

Hi all
just a thought, what about a set of cvt pulleys like were used on the early 80 Honda odessys these all allowed the motor to idle but run without a gearbox.
From memory they used two spring loaded pulleys that the drive belt slipped into effectively offering a completely stepless transmission.
it would be a ***** sorting out the spring tensions so it worked effectivly, but not impossible.

I have read about guys with superchargers using wastegates to limit boost for different conditions. Basically let air out to lower boost while cruising around on pump gas, and retaining that air while at the track on race gas. This has the effect you're going for to a certain degree. What I mean by that is that it will allow fast spool up of the supercharger creating full boost at low rpm. A wastegat of course cannot turn off the supercharger like you would want in a clutch type setup.

I agree a clutch for out SN blowers would be awesome if it could be done as you suggest. This is especially true because they use so much power to run at all times even when not creating boost.

Just look at the origins of your own supercharger. It was originally a McColloch and had a two step transmission behind the pulley that was in high gear from idle, and slowed down when you revved it so as to not overspeed the blower. Later they got rid of the 2speed trans and called the new design a Short Nose supercharger or.... wait for it...... the SN series.......