Vacum tree

[63viking]

It seems I have two..

[EDBS0]

I have sold my Riviera and manual but from memory this is related to the supercharger's function. Under normal cruising the supercharger is in a bypass mode and will not build pressure. Think of a bypass flap being held open and no or little pressure being built. When you want to accelerate the bypass would be shut off and full pressure available immediately.

It is an elegant system where little power is lost at cruising and full power available at WOT. It has to do with reducing the parasitic loss of the supercharger.

[padgett]

Think that is pumping loss but with an upstream throttle plate the rotors are operating in a near vacuum at cruise anyway. I wonder if it has more to do with limiting the max pressure at WOT.

[EDBS0]

Quote:

I wonder if it has more to do with limiting the max pressure at WOT.

I don't think so. By putting on a smaller pulley, which I did, drives the supercharger at even higher speeds and pressures. I got and others to a big increase in hp so there is no limiting pressure. I sold the manual with the car but I do have a clear recollection that it has to do with reducing parasitic losses.

I have been wrong before and will be again but am more than reasonably certain here.

I think it just dumps the air back before the screws reducing pressure.

[Reattaron]

BY PUTTING ON A SMALLER PULLEY ON THE SUPERCHARGER,DO YOU ALSO
NEED TO CHANGE THE SERPENTINE BELT ?

[Greg Ross]

To answer the Belt question, no. The tensioner takes up the slack.
The Vacuum tree you picture is the port that feeds utility vaccuum for accessories, vaccuum to the Fuel Pressure regulator and the Boost Recirc. Butterfly. To see it you have to split the Blower off the Dome, the butterfly blade opens and allows compressed air to recirculate into the Intake.
The solinoid Valve immediately below it turns the buttefly and disables boost when the car was put in reverse and supposedly in an over-rev condition. Apparently when swapping these S/Cs in you should just leave the solinoid with no power lead. The engine vaccuum alone looks after itself.

[EDBS0]

On my 1996 Riviera I did not have to shorten up the belt. I used a Goodyear gatorback belt. They are one of the most slip resistant belts out there.