? About by-pass valve...

SCUPERCHARGED

Registered User
I know on turbo cars and centrifical superchargers they have bypass or blow off valves that blow the unwanted boost into the atmosphere and make that psshhh sound. I know that we have bypass valves but it doesnt make a noise. Do they make those for our roots type? If so where can they be purchased? Sorry if that was a stupid question! Im more familiar with turbo systems.
 
if all your after is that super cool "psssh" sound,yes it can be done. on the sc's setup though you'd be "psssshing" off metered air,so in between shifts the car will run rich and backfire,esp if you have no cats and a freeflow exhaust.
 
A blow-off valve used in turbos is to relieve pressure when it reaches a set limit. Usually this happens because they are boosting the charge in the intake plumbing - before the throttle - so when the driver lets off the gas pedal and the throttle plate slams closed, there is a huge pressure spike in the intake. So the blow-off valve vents the excess pressure out.

This causes alot of issues with PCM controlled cars that meter the air flow with the MAF - since it determined how much air came in, and adjusted the fuel ratio for that - if that is then dumped you'll get an flash rich situation....

Our by-pass valve work very differently. Since the supercharger is inline with the intake - it actual restricts the air flow at low rpms. So under low rpms, where the engine is under high vacuum, the valve is open allowing some of the intake air to 'by-pass' the supercharger and go directly into the intake.

Once there is more rpm, and then engine vacuum is low, the valve closes forcing all intake air to go through the supercharger into the manifold - no by-pass.

there is no reason for a blow-off valve in our setups since the supercharger (and all the boost) is after the throttle plate.
 
First, the original question has been answered. Our system is closed and ALL the air that travels through the MAF goes through the engine. Any kind of "blow-off" valve will mess up the air/fuel mixture. Our "cool factor" is blower "whine" :D . FWIW, there are mods that enhance this sound quite nicely

Second, supercharger operation in an SC is often misunderstood. Since it is driven from the crank, its speed is directly relative to engine RPM. This means that it always moves (pumps) the maximum amount of air it can for any given inlet pressure and RPM. Our blowers are a "positive displacement" type. They do not "compress" the air charge; they move separate "parcels" of air through the case, and they do it by force (hence the term "positive displacement"). Compression (boost) is the result of all those "parcels" getting squeezed into the intake tract.

Constantly boosting* air requires extra HP to turn the blower. At idle and light cruise we really don't want to waste power trying to boost* the intake charge (because we don't need to), so a bypass valve was designed into the system. This allows a portion of the boosted* air from the supercharger output to "re-circulate" back into the supercharger inlet through the bypass valve. In effect this "equalizes" the inlet and output pressures and removes the supercharger load from boosting*. This greatly reduces the amount of power required to turn the blower. Ford measured the HP required to turn a blower with the bypass valve fully open to be roughly 1/2HP; without it about 4HP. Since the blower is "in effect" free-wheeling, blower wear is also reduced. One last benefit of the bypass valve is improved "driveability".

*Note - Boost in this case is the output pressure relative to the inlet pressure of the supercharger.
 
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