Technical fuel pressure control valve placement question dazed and confused

i see some regulators plumbed in before the carb and some after the carb. i am refering to by-p*** fuel pressure regulators. What is the advantage to either one?

 

Its' a controlled leak, placement would be for aesthetics and convenience for a byp*** regulator (a deadhead would be different).

 

What does the carb and pump require?

 

The biggest advantage of a byp*** regulator which maintains a fixed pressure to the feed line, but returns excess fuel to the tanks is the cooler fuel at the carb.

I'd also guess that it is less restrictive in most cases. The fuel from the tank, up thru the lines to the fitting has no restrictions. With an inline regulator, it's got to have a diaphragm and a valve to hold the pressure at the outlet, which means a small gate it opens and closes. Can it flow enough at WOT for as long as you hold the pedal down?

 

The ones plumbed after the carb are usually a "return valve" that controls the whole line pressure between the pump and the regulator.
This method allows for fuel recirculation.[cooler fuel and no vapor lock] But the whole system between the pump and return valve has the same pressure

This ^^^ is a good method when using an EFI pump on a carb.
For modern "Jungle Juice" you really need 15-20psi pressure on the whole system to prevent vapor lock.
So a return valve can hold this pressure throughout. But you need to T off a 2nd deadhead regulator that is close to the carb as possible.[eg: 4-7psi]

Usually the regulators that are before the carb are the deadhead variety the only allow the preset pressure to p*** [similar to a regulator on a propane bottle]

Modern fuels [jungle juice] really need pressure to stop vapor lock. One problem is cause by the "draw" or vacuum between the tank and the pump. This lowers the volatility and problems can occur when the fuel meets a hot fuel pump.

I've had great success with EFI pumps with Carbs [in road race cars] by using a return valve AND a deadhead regulator method.
Even a lowly 4 cylinder Ford Focus OEM pump flows 0.5 gals/min [30 gals/hr] at 39 psi . When you drop the pressure to 15-20 psi using a return valve it flows about 50 gals/hr which is enough for a 500 hp carbureted engine.

Just remember Pressure is Pressure and Volume is Volume [don't confuse the two]

 

@Kerrynzl do you have any deadhead regulators you can recommend?
It seems like the Adjustable Holleys are often used, but the others are 'consumer' grade at best.

 

Many NOS racer still use the
Holley Blue dead head Regulator
On Multi stage kits ,
I use ***ortment or Aeromotive , Holley's Billet,
Old cast Holley's & Enderle popet's

 

I have a Tanks Inc pump in my roadster, these pumps produce around 60 PSI and 55 or so gallons per hour. To knock that kind of pressure down so my Stromberg's don't explode requires two fuel pressure regulators as there is no single regulator I could find that could turn that pressure down to 2-3 PSI.

The big regulator is on the frame rail with a return line the same size as the feed line. Micro filter in line before the regulator. This reg knocks the pressure down to 4-5 PSI.

That reg feeds the firewall mounted fuel filter and then the Holley 12-804 that I mounted on the back of the blower. You can see it in this picture on the back of the carb adapter feeding the fuel distribution block. The 12-804 can take 5 PSI and knock it down to 1 PSI. I have it set at 2.5 which seems to be perfect for my set up.

 

On Most Good quality regulators there's different part numbers and different operation PSI ranges of fuel pressures they work between , Not all Work from 0- as much as 100 psi ,
I have a Few Holleys working PSI
0- like 5 spi , Pretty much all of them Billet are in the $180 plus range .

 

On my O/T Falcon NZV8 Racecar we used a non-byp*** Holley that T'eed off next to the carb [It was very close, to the carb]
My Friend made an Adjustable [spring pressure] Check valve for the return valve. This valve doesn't open until the pressure is met/exceeded.
Note: I've also seen this ^^^ done with a restrictor [jet] in the return , BUT this is wrong because Pressure is Pressure and Volume is Volume

The pump on my racecar was a 6 cyl Falcon Bosch EFI pump.

Ford EFI pumps are 39 psi , but what you mentioned about 2 regulators was basically what we did
We reduced the whole system to 15-20 psi [tune-able] with a Return-valve or Dump valve which required pressure to exceed the required value to open a return.
The line pressure prevented vapor lock [when they banned 100 octane leaded]

Going from 15-20psi down to 4-7psi required a simple Holley deadhead regulator.

When the "almighty wise ones" banned 100 octane leaded, vapor lock /hot start issues happened [Don't stall on the track]
So all the racers switched from byp*** to deadhead systems which sort of helped. BUT the life expectancy of an electric pump was usually 1-2 meetings [the Mallory lasted the longest]

We never had an issue with pumps or vapor lock using an OEM EFI pump and return [the one I used I grabbed from our local U-Pull as an experiment and it stayed for good]

 

Might be O T what this post about
When dealing with 45 ish & Higher
(&'low)
Fittings make a diffrents in high flow volume and pressure , non smooth bore radius can creat turbulence in the system creating air bubbles /cavitation & not a steady flow of liquid