I have a friend that was asking me about how Studebaker superchargers worked. I showed him some of the pictures, but he has questions that I could not answer. #1At idle there is no boost, but as the RPM's come up what triggers the boost. #2When the boost comes up, how does the fuel pressure in the carb come up. Or is the fuel pump pressure always much more powerful then the boost? #3While at idle you have vacuum on the intake manifold. But after the boost takes over,what protects the diaphragms outside the boost box, like the power brake and distributor vacuum advance. #4Also since you have positive pressure, how does the vacuum advance work since the RPM's have come up and then there is no vacuum for the advance.
The rpm of the blower must be increased to begin creating any boost.
The fuel pump has a static preset pressure set by an internal spring at @ 6-7 PSI.The pressure created by the blower is sent by a pipe from the intake manifold or carb box to add to that fuel pressure as boost pressure rises.For example, the idle fuel pressure is 6 PSI - at full boost pressure of @ 6PSI, the pressure sent by the pipe to the top side of the fuel pump diaphragm adds to the spring pressure - so 6 PSI pressure from the spring ,plus 6 PSI air pressure "signal" from the manifold equals 12PSI. The Carb is pressurized by the blower and actually only "see's" the 6 PSI spring induced fuel pressure above the static. In effect the fuel pressure stays at the preset spring pressure on the pump, and the air pressure fed to the fuel pump diaphragm raises the pressure at a level equal to the boost,whatever the boost pressure is at any time, causing the carb to "see" 6 PSI at all times.
As to the brake booster it may have a check valve but others smarter than me can be more specific. But as to the distributor advance unit - Lowering the timing under boost is a good thing for supercharged engines.It increases power and prevents detonation. The boost pressure applied to the advance unit lowers the timing a tad, I'm unsure as to how much.It will only lower the timing to a level that is the same as removing the pipe to the distributor -the diaphragm rests against a "stop" until it sees vacuum. Removal of the vac/pressure line to the distrubtor and checking the timing at full mechanical advance could give you the total timing under boost , unless the carb signal line produces a vacuum even under boost. ( I personally would use actual intake manifold vacuum/pressure to signal the distributor,to use the timing retard feature.)
I hope the previous reply above helped you with this question.The mechanical advance inside the distributor raises the timing. Static timing + mechanical advance + vacuum advance will give you your total timing. Subtract the Vacuum timing numbers when under boost.
I have very little hands on experience with a supercharged Studebaker, but my Son has a 1965 VW bug that uses the Studebaker style Blow Thru system with a turbocharger.(Harbit-ized!) Using a 100 cubic inch VW air cooled engine he has gone a Best E.T. of 6.48 and a best MPH of 105.6 (1/8 mile stats). Rising rate fuel pressure, boost retard timing,and pressurized carburetor, just like Studebaker did it in 1957. The guys in the pits at the strip can't figure out how it all works. That old technology is too much for them to comprehend. B.T. Tuttle strikes again, much to the chagrin of the Mustang/Camaro fans.
Here' s some added info. The brake booster usually has a check valve but it doesn't matter too much because as soon as you lift your foot off the gas to hit the brakes, the engine is producing vaccum. Same with the vacuum advance. The vacuum advance only works at light throttle. Remember that the supercharger only pressurizes the air above the throttle plates. If you are cruising, the air in the intake manifold is still under vacuum.
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