Thanks,

Rono.

Let’s see if I can make this sound simple.

Running a separate line from the carb hat to the fuel pump diaphragm allows the pump to sense the amount of boost pressure being supplied at the carb.  This makes the fuel pump 'boost referenced'.  In essence, if the fuel pump is putting out 6 psi pressure under normal circumstances, then by being boost referenced it will maintain this 6 psi fuel pressure over the amount of boost being supplied.  Under normal driving conditions where no boost is being generated, then fuel pressure is normal at 6 psi.  As the throttle opening is increased, then boost pressure goes up and the fuel pump automatically senses the amount of boost over atmospheric and maintains the 6 psi fuel pump pressure above the amount of boost being supplied.

Stated differently, if the boost pressure at the carb is 6½ psi, then the fuel pump will be putting out 12½ psi assuming the fuel pump delivers 6 psi at atmospheric.  The 6½ psi boost pressure at the carb is also being seen at the fuel pump diaphragm by use of the connecting line and the fuel pump automatically puts out its normal 6 psi above this.  If the pump is not ‘boost referenced’, then the pump is putting out only 6 psi all the time which is in essence a ½ psi short of being able to keep up with the fuel needs of the carb when pressure at the hat is 6½ psi.

Thanks for your reponse. I understand the principle, but I'm still confused on the mechanics (sorry). First, can you give me a year or model fuel pump you would modify? I have heard that the earlier fuel pumps with the vacuum ports on top won't work because they are not located in the correct place. Also, when you say that the line would run to the "carb hat", where would that be on a 4bbl? I haven't decided on a particular 4bbl yet, (*any suggestins) but Iknow that most of them will have a vacuum port for the dizzy avance and another or the PCV valve.

The VS-57 unit I bought was set-up for a Kaiser 226 and came with the carb and pressure box that sill had the selenoid atached to the linkage. Can I use this selenoid on a 4bbl set-up as the secondaries kick in?

Thanks again.

Rono.

A fuel pump for a 390/427/428 Ford FE would be a good place to start.  Preferably a pump that can be taken apart and a pump with the larger inlet/outlet fuel ports.  The 427/428 CJ pumps are already a higher volume rated pump so these would be ideal to start with. 

As Eric and Chuck both mention, the pressure pickup for ‘boost referencing’ can be taken anywhere after the blower discharge exit, not just at the carb ‘hat’.  Here are some pics of carb hats with some having the boost reference line located at the hat and others at some point before that.

THANKS!! A picture (or 2 or 3) is worth a thousand words. Thanks also for the fuel pump recommendations.

Rono.

One other thing.  I have found two rebuilt fuel pumps with no diaphragm stem seal.  Without that seal, it is impossible to pressurize the back side of the diaphragm.  So now I always check my pressurized pumps with shop air and a regulator to make sure they can contain at least blower boost pressure.  Moonshadow had one a few years ago at Columbus that couldn't be pressurized, caused him all kinds of headaches.  I believe it was an FE pump.  Chuck?

I run a Holly Red Top electric fuel pump in my Customline now. Is this the type of pump you had set-up with a switch for hard runs? Also, what ype of pressure does your mechanical pump put out? I'm still trying t figure out the right type of pump (single or dual diaphram). Do you use one of those overflow fuel filters that sends extra fuel back to the tank? I know...ls of questions

Thanks,

Rono.

Rono

dan

Without an electric pump, your mechanical pump has to "suck" the fuel from the tank, then pressurize it to the level required to fill the carb.  With the electric pump added it will charge the mechanical pump with pressure, negating the "suck" requirement.  The boost reverenced mechanical pump will still provide the needed pressure, so the electric pump doesn't need to supply the total pressure.  On your test stand engine, you may not even need an electric pump, the mechanical pump may be enough since it doesn't have to deal with a long fuel line and the inertia of the car accelerating.

those were my thoughts, but having never dealt with any engine under boost, this is a new ball game to me.

I did notice that the original paxton mcculloch VS57 instructions seemed to have the electric fuel pump mounted down the line from the mechanical pump (between the mp and carb)? Do you think I should go ahead and mount the electric fuel pump before the mechanical pump?

All of this may be moot considering there is no load, but I would like to go through the mechanics of getting everything as it should be if installed in a vehicle and put under load. There may be some dyno time later on...once I get that cam installed.

I have already tested the teapot (with no boost) and I was very pleased. Out of my "box" the carb performed very well. I will have to make some final adjustments when it gets under boost and fully warm, but after my rebuild and all of the blow through mods, it started, idled, and went to WOT very quickly with no hesitations.

And then, there is always the possibility of being able to talk my father-in-law into letting me install it into his 55 Club Sedan later this winter after the car show season is over. The 292 I put in that vehicle runs so well naturally aspirated, it may be hard to convince him!

        I run a Mustang (aftermarket) in tank pump with a 40 lb rating. I control that with a bypass regulator that is "Boost-Referenced". It increases the pressure to the carb as the boost pressure increases. The object being to keep the carb fuel pressure about 6 lbs. more than what the blower is delivering. I do this because I Don't have a real Blower fuel pump. Those pumps are rare and expensive. Clear as mud?