[Tom Vaught]

So far we have discussed several subjects as related to the Holley Carburetor.
The Bonnet that fits over the Carb Air horn, the Pressure Box that can fit the Holley carb inside,
and and the Draw thru System where the Carb has a regular Air Cleaner installed on the airhorn.

If you have a Blow Thru Boosted System the Holley carb is down stream of the Boosting Device, be it a Centrifugal Supercharger or a Turbocharger.

If you suddenly slam the throttle shut, say at the end of the MPH Lights, the Boosting Device is still spinning close to max rpm (be it a Turbo or Centrifugal compressor.

When you do this the Compressed Air in the ducting from the boosting device to the carb bonnet has no where to go. This pressure spike is very hard on the Boosting Device. If it is a belt driven deal then the belt tries to remove itself from the drive pulleys. If it is a Turbo the Turbo goes into massive surge and tries to bend the compressor blades into undesirable shapes. $$$

So we need to somehow remove the potential for pressure spikes in the plumbing.

For mind boosting systems Bosch made a "compressor By-Pass Valve that would bleed off the pressure in the system using a 1" Hose plumbing system. See Pic #1.
It was ok for very mild systems but lacked the ability to remove a bunch of air quickly and protect the Holley carb and the boosting device.

So I have included a couple of diagrams of how the parts fit and work in two modes: Open Mode and Cruise Mode.

In Cruise mode the air from the turbo (for example) follows a normal path thru the turbo and then goes to the open throttle plate on the carb.

In the open mode the Throttle plate is closed and now the by-pass valve is open and lets the air that can't go thru the engine any longer do a race track pass thru the compressor by-pass valve, thru the turbo and the back to the compressor by-pass valve to begin the "loop circuit" again.

A Blow-Off Valve would just dump the air into the engine compartment instead of recirculating it thru the Turbo.

So you have a picture of a "baby" Bosch CBV and pic #4 is a Race MONDO CBV with a much much larger valve. But the real high HP engines actually need two of the Mondo Valves many times. They are Basically Blow-Off Valves.

So the idea is Protect the carb and the boosting device by using a tool that relieves pressure on quick throttle closure events.

Tom V.

I will try to post the other images tomorrow.