supercharger bypasses...

[Hot Rod JayRad]

I was giving some thought to superchargers and ways to deal with thier power-sapping nature and was hoping someone could shed some light on the ways its been done in the past.

I dont mean to sound stupid, but I really dont have much experience with the different kinds of superchargers. I was wondering if there was a way to put a centrifugal clutch to disengage the supercharger after a certain rpm? Or are there systems that bypass the superchargers after a certain rpm? And how would this work with the 20mm restrictor we run?

Thanks guys!

[drivetrainUW-Platt]

On the magnachargers for LS1 engines, they have a bypass valve that bleeds off boost at cruizing on the highway so it only takes a few hp to run it. I assume it is vaccuum operated and when you give it gas it shuts and goes into regular boost.

With this system, they claim that on the highway, you will see next to no difference in fuel economy since it isnt taking much work to spin the super over.

[Wesley]

Really, that is the most practical way to lessen the power loss of a blower - just have it compress less air and blow off some at low load. It doesn't take much power to drive the guts - it's the compression that takes the most.

Also, the smaller the volume, the less power it will take to run. I don't see why you couldn't pull a Mad Max and put a clutch on your supercharger, but an electric clutch powerful enough to hold it would be bulky and draw a lot of power.

If you use a centrifugal clutch (a la go cart or chainsaw) you are going to lose a lot of power to the clutch itself, and also reduce effectiveness of your supercharger at low RPM - where a supercharger shines over a turbo.

[drivetrainUW-Platt]

straight from the horses mouth:

Why do you need a bypass valve? The best kept secret in forced induction is the little known bypass valve. This small valve, when properly installed between the supercharger and the air throttle body, allows the supercharger to become extremely efficient in terms of economy and parasitic power loss. Our M90 supercharger uses less than 1/3 of 1 HP at 60 MPH cruising. The bypass is operated by a vacuum actuator control unit that is normally closed. When vacuum is high (idle-cruising) the actuator opens the bypass valve, equalizing the vacuum pressure throughout the system. When boost is required (accelerating) the vacuum is decreased and the bypass valve instantly closes, causing pressure to increase into the cylinders. This equalized vacuum condition virtually eliminates the normal parasitic power loss of a forced induction system.

http://www.magnusonproducts.com/bypass.htm

[Wesley]

I take it this is an external centrifugal-type supercharger?

A Roots-style might be a little harder, but the concept is the same.

[Grant Mahler]

Wesley - I hope you are referring to positive displacement superchargers (roots, lysholm, whatever) when you commented that they produce boost/power lower.

Once turbo's achieve the flowrate necessary to build boost, they do. A turbo can sized to build boost at nearly ANY RPM. The tradeoff of course being that too small a turbo will simply blow hot air at higher RPM.

A "centrifugal" supercharger builds boost as the square of RPM. This would not produce more power than a turbo at low RPM, because boost doesn't come on in serious amounts until higher RPM.

To the OP - Mercedes (among others) uses clutched superchargers. Go to a dealership and look at how they do it.


just my $0.02

[Mike Flitcraft]

http://www.whipplesuperchargers.com/
http://www.whipplesuperchargers.com/videos/GT40.MPG

My personal favored choice on blowers, but I favor turbos above them by a decent amount for a reason.

[Wesley]

Grant - yes, sorry, I meant positive displacement. Centrifugal is a fancy turbo on a pulley.

And I do agree, turbos can be sized effectively like you said, but theres just something about superchargers...a je ne sais quoi.

[Bill Kunst]

The bypass valve uses vaccum from the throttle blade-engine side and releases pressure of the blower to throttle side. It is for a standard style setup that we do not have and stops the blower from experiencing major surges, just like a turbo would experience. it works like a fuel pressure regulator.
Bill kunst

[Parker]

The eaton blowers on the Mercedes Kompressor cars of the late '90s/early '00s is controlled via an electric clutch. I'm not sure about the newer ones, but we used to use them making junkyard supercharger kits.

[iolair]

If the throttle is placed before the inlet of the supercharger and since the throttle cruise open angle is generally very small, how much air is actually being compressed in this context?

I'm wondering why a bypass valve is even needed.

John

[Bill Kunst]

its really not needed. I thought that is what I was saying when I mentioned that it is used in a standard Tb position system, not FSAE layout.
Bill