Good morning, Here's some nighttime reading! Your question to the Avanti chatgroup regarding the fuel pressure...( my experience...45 years) Old technology: On Studebakers applications that used a Mcculloch/ Paxton, you have to understand that the boost was designed to only be applied infrequently and for short periods of time( for acceleration). Their method of fuel pressure regulation was to connect the output volute of the blower to the top of the fuel pump, with a steel tube, so that the dynamic air pressure ( boost) would act on the FP diaphragm and raise the fuel pressure proportionate to the boost. The fuel pressure is only added to prevent fuel from reversing flow in the carb and fuel lines. The static setting of the carb jetting in all their supercharged applications, provided a constant rich atmosphere to the engine, in all phases of operation, boosted or not. The rich condition was required, so that when the boost came on, the denser charge prevented detonation. The richer mixture cooled the charge with added fuel. When you raise the fuel pressure, it goes up pretty quick because of the ratio of the blower planetary gear. (This principle was more critical on the early McCullochs because the variable ratio pulleys would open in a heartbeat and the pressure could spike.) The rise and fall of engine rpm can't use the fuel pressure in the delivered amount, so what happens to it? This was one a drawbacks of supercharging in this manner and to solve the problem in the McCulloch applications, you have to look at the rear bottom of the airbox (rear). You'll find a small diameter drain tube, which was terminated around the intake manifold. This was designed to vacate raw, excess fuel which puddled on the inside floor of the airbox when the fuel pressure spike exceeded demand and blew gasloine out the top vent of the carb. If you ever watch a departing Golden Hawk, Packard Hawk or Sedan, that has the drivers foot in it, There will always be twin trails of black smoke coming from the exhaust, due to the very high mixture resulting from the designed in jetting and the overload of fuel in the airbox. It worked better in a passing situation, as the engine prm was much higher to begin with, but was still evident. There was also a flapper valve on the airbox to open when the engine was stopped to allow evaporating, undrained fuel to vent out of the system. The Avanti application was a bit different because of the constant blower / crankshaft speed ratio. This setup still had the rich jetting, but at highway speeds, the blower pressure was kept in play moreso. The fuel pressure compensation requirement was still there, as were the drawbacks of over pressure but in their attempt to solve other non-related problems, cured or compensated some of the boost condition ones. The Avanti has known underhood temperature problems, which produces a problem called fuel perclolation. This occurs when fuel is kept standing in a line ( by the action of the needle and seat in the carb) and being close to a high temperature point, results in the fuel boiling, thus displacing fuel with pockets of air (?) and starving the engine until it stalled (embarrasing moment) To counter this problem, the engineers added a return fuel line to the gas tank that originated at, what looked like a fuel filter with a glass bowl close to the carb. There was a tee'd connection which routed fuel back to the tank and kept the fuel cooler, by having a constant flow, to and around the carb. What they didn't realize, was that the return fuel line also acted as a high pressure fuel bypass in a boost condition. So the action of blower, when you stepped in it was a smoother increase of power with a considerable decrease to the black trail from the exhaust. There was still the flapper valve on the R2 to vent gas which puddled on the stove under the carb inside the intake manifold, but the carb was sealed to prevent fuel from blowing out onto the engine. The R3 only had the flapper, as far as I know, and the carb doesn't need to be sealed because its contained like the Golden Hawks. Some of the early Avanti II's still had this return line. Later ones had it removed, although the fitting on the tank is still there, but soldered closed. New technology: When I decided to supercharge my A-II, I went through all the machinations of attempting to replicate the Studebaker engineering. I labored to make a fuel pump with a fitting on the upper casting. That didn't work too well, so and old Hot Rod issue had what I thought was needed. Their article on supercharging a 'modern' car with a Paxton, had the solution as being " route the fuel from the pump to a Holley FP regulator. Then modify the regulator to emulate the top of the Stude type fuel pump". So I pruchased a Holley Blue which came with their FP regulator and modified it as described. This worked somewhat, but in too many situations, the fuel pressure would overcome the regulator and flood the carb, resulting in more embarrasing situations... My complaints to Holley went unanswered. What I finally came up with was kind of like a "Studebaker" solution. I fabricated a return fuel line to the fuel supply. Remember, I had an electric fuel pump ( mounted inside the passenger side front hog trough outrigger), so the return merely had to be routed to the line supplying the pump, not all the way to the tank. Then I purchased a Mallory 4309 regulator, which has 4 ports. port 1 is the supply, 2 is to the carb, put an electric fuel pressure sender in the third and routed the 4th back to the pump input fuel line. This works very nicely. The carb is an Edelbrock with a rod size increase to provide the static enrichment at both cruise and power. I bolted an R3 airbox to am Edelbrock Performer manifold. The blower was made for me by John Erb with a tighter pressure spring pack and high output impeller. My engine is a Jasper Class II 350/330 Hp before supercharging ( 8:75 compression). Must put out around 450HP at full chat. I gave Lionel Stone the specs of all my work and now he's selling Avanti II Paxton kits, but all the stuff is on my website anyway. The only other way to apply a blower these days is to use a 96 or later chassis with OBDII diagnostic connector and tweak the injection system with a laptop/software. You might have to buy a performance processor chip to achieve the best output. This type system would alleviate the extra rich condition required by mechanical components. ============= Good morning, Here's some nighttime reading! Your question to the Avanti chatgroup regarding the fuel pressure...( From my 45 years experience...) Old technology: On Studebakers applications that used a Mcculloch/ Paxton, you have to understand that the boost was designed to only be applied infrequently and for short periods of time( for acceleration). Their method of fuel pressure regulation was to connect the output volute of the blower to the top of the fuel pump, with a steel tube, so that the dynamic air pressure ( boost) would act on the FP diaphragm and raise the fuel pressure proportionate to the boost. The fuel pressure is only added to prevent fuel from reversing flow in the carb and fuel lines. The static setting of the carb jetting in all their supercharged applications, provided a constant rich atmosphere to the engine, in all phases of operation, boosted or not. The rich condition was required, so that when the boost came on, the denser charge prevented detonation. The richer mixture cooled the charge with added fuel. When you raise the fuel pressure, it goes up pretty quick because of the ratio of the blower planetary gear. (This principle was more critical on the early McCullochs because the variable ratio pulleys would open in a heartbeat and the pressure could spike.) The rise and fall of engine rpm can't use the fuel pressure in the delivered amount, so what happens to it? This was one a drawbacks of supercharging in this manner and to solve the problem in the McCulloch applications, you have to look at the rear bottom of the airbox (rear). You'll find a small diameter drain tube, which was terminated around the intake manifold. This was designed to vacate raw, excess fuel which puddled on the inside floor of the airbox when the fuel pressure spike exceeded demand and blew gasloine out the top vent of the carb. If you ever watch a departing Golden Hawk, Packard Hawk or Sedan, that has the drivers foot in it, There will always be twin trails of black smoke coming from the exhaust, due to the very high mixture resulting from the designed in jetting and the overload of fuel in the airbox. It worked better in a passing situation, as the engine prm was much higher to begin with, but was still evident. There was also a flapper valve on the airbox to open when the engine was stopped to allow evaporating, undrained fuel to vent out of the system. The Avanti application was a bit different because of the constant blower / crankshaft speed ratio. This setup still had the rich jetting, but at highway speeds, the blower pressure was kept in play moreso. The fuel pressure compensation requirement was still there, as were the drawbacks of over pressure but in their attempt to solve other non-related problems, cured or compensated some of the boost condition ones. The Avanti has known underhood temperature problems, which produces a problem called fuel perclolation. This occurs when fuel is kept standing in a line ( by the action of the needle and seat in the carb) and being close to a high temperature point, results in the fuel boiling, thus displacing fuel with pockets of air (?) and starving the engine until it stalled (embarrasing moment) To counter this problem, the engineers added a return fuel line to the gas tank that originated at, what looked like a fuel filter with a glass bowl close to the carb. There was a tee'd connection which routed fuel back to the tank and kept the fuel cooler, by having a constant flow, to and around the carb. What they didn't realize, was that the return fuel line also acted as a high pressure fuel bypass in a boost condition. So the action of blower, when you stepped in it was a smoother increase of power with a considerable decrease to the black trail from the exhaust. There was still the flapper valve on the R2 to vent gas which puddled on the stove under the carb inside the intake manifold and the carb was sealed to prevent fuel from blowing out onto the engine. The R3 only had the flapper, as far as I know, and the carb doesn't need to be sealed because it's contained like the Golden Hawks. Some of the early Avanti II's still had the return line. Later ones had it removed, although the fitting on the tank is still there, but soldered closed. New technology: I've owned a 57 GH and a 64 R2, so when I decided to supercharge my current 1970 A-II, I went through all the machinations of attempting to replicate the Studebaker engineering. I labored to make a fuel pump with a fitting on the upper casting. That didn't work too well on a Chevy pump, so an old Hot Rod issue had what I thought was needed. Their article on supercharging a 'modern' car with a Paxton, had the solution as being " route the fuel from the pump to a Holley FP regulator. Then modify the regulator to emulate the top of the Stude type fuel pump". So I purchased a Holley Blue which came with their FP regulator and modified it as described. This worked somewhat, but in too many situations, the fuel pressure would overcome the regulator and flood the carb, resulting in more embarrasing situations... My complaints to Holley went unanswered. What I finally came up with was kind of like a "Studebaker" solution. I fabricated a return fuel line to the fuel supply. Remember, I had an electric fuel pump ( mounted inside the passenger side front hog trough outrigger), so the return merely had to be routed to the line supplying the pump, not all the way to the tank. Then I purchased a Mallory 4309 regulator, which has 4 ports. port 1 is the supply, 2 is to the carb, put an electric fuel pressure sender in the third and routed the 4th back to the pump input fuel line. This works very nicely. The carb is an Edelbrock with a rod size increase to provide the static enrichment at both cruise and power. I bolted an R3 airbox to an Edelbrock Performer manifold. The blower was made for me by John Erb with a tighter pressure spring pack and high output impeller. My engine is a Jasper Class II 350/330 Hp before supercharging ( 8:75 compression). Must put out around 450HP at full chat. I gave Lionel Stone the specs of all my work and now he's selling Avanti II Paxton kits, but all the stuff is on my website anyway. The only other way to apply a blower these days is to use a 1996 or later chassis with OBDII diagnostic connector and tweak the injection system with a laptop/software. You might have to buy a performance processor chip to achieve the best output. This type system would alleviate the extra rich condition required by mechanical components. Bob Johnstone Potomac Chapter, SDC