Stewart-Warner Electric Fuel Pump

[Bob B.]

Hi all,

I have a S-W electric fuel pump mounted on the frame of the '57 race car I'm restoring to as-raced, but nothing connected yet.





The mechanical pump speed, since it runs off the cam, varies according to rpm, but the S-W would have constant speed and constant pressure. The fuel bowl float closes the pin that lets in fuel, but what about the pressure on the line? Would that constant pressure make the line prone to leaks?


I have a S-W fuel pressure gauge mounted in the dash and a sender is coming any day, but would using two pumps make the pressure too high since there is no return line?


If the S-W electric pump conked out, could the mechanical continue working or is there some restriction in the S-W?


And if the mechanical conked out, is there some restriction in the mechanical that would impede flow from the S-W?


Thanks,

Bob

[Mark F.]

Re: Stewart-Warner Electric Fuel Pump

Hi Bob,

My experience with this goes back ~50 years with my 1938 85-hp. flathead Ford - so, it may be irrelevant to your situation, but here goes anyhow -

My dad and I could not keep that sucker running (long story), so we eventually installed an electric fuel pump back near the gas tank (the original push-rod fuel pump was left in place). When I'd turn the ignition on, you could hear the electric fuel pump "clicking" as it pressurized the fuel line - and yes, it was under positive pressure from the electric pump up thru the OEM fuel pump and then to the carb. I have no idea what make it was, nor do I remember if it had a controllable pressure regulator. I do know it pressurized as soon as the ignition was turned before pressing the start button on the dash (remember them?). So with that wiring configuration, if you stalled the car and the ignition was still on - you'd still have FULL pressure in the line (whatever it was).

Now that I'm much older and gray, I'm thinking that long length of positive pressure fuel line from the rear of the car to the front is (was) not a good idea. If I was to do that again, I would have tried to have it as close to the front end of the car as possible - also, I'd have a good fire extinguisher (which I did not carry at the time). The newer electric pumps may have many more safety features than what was in mine...I just don't know - and I also can't answer your last 2 questions as I simply can't remember how the guts of the electric I used were controlled.

I will tell you after installing it, the car ran like a hot rod! Man, no lack of fuel to the carb - and in that thing, it sounded like the engine was going to blow at 10mph in first gear...

good luck - hope it works out for you...

[Jim L.]

Re: Stewart-Warner Electric Fuel Pump

Hi all,

I have a S-W electric fuel pump mounted on the frame of the '57 race car I'm restoring to as-raced, but nothing connected yet.

It's a good bet you've got an SW 240 pump. Can you post a picture?

The mechanical pump speed, since it runs off the cam, varies according to rpm, but the S-W would have constant speed and constant pressure. The fuel bowl float closes the pin that lets in fuel, but what about the pressure on the line? Would that constant pressure make the line prone to leaks?

The mechanical pump pulse rate will vary with RPM but not the pressure. The pressure limit is determined by the internal spring pushing on the diaphragm. You don't have an issue here.

Regarding your question about leaks, no.

I have a S-W fuel pressure gauge mounted in the dash and a sender is coming any day, but would using two pumps make the pressure too high since there is no return line?

No. The pressure is not additive. It will be the pressure created by the higher of the two pumps. As long as the needle/seat/float can resist that pressure, there is no issue.

If the S-W electric pump conked out, could the mechanical continue working or is there some restriction in the S-W?


And if the mechanical conked out, is there some restriction in the mechanical that would impede flow from the S-W?

If the mechanical pump quits, the electric pump can probably force fuel by the internal valving of the mechanical pump.

I suspect the electric pump is of the positive-displacement variety. If that's true, my hunch is that the mechanical pump can NOT pull fuel through it if it dies.

[Rocco S.]

Re: Stewart-Warner Electric Fuel Pump

Just a few suggestions.

1. Back in the day I remember that most aftermarket electric fuel pumps were better at "pushing" fuel than "sucking" fuel and were always located close to the fuel tank.

2. The use of a fuel pressure regulator was required to reduce the line pressure to the carburetor since the needle/seat had its limits. Around 6 PSI comes to mind.

3. And most important, NEVER install a fuel pressure gauge inside the passanger compartment unless it is an electrical gauge. Mechanical pressure gauges require a pressureized line running inside the car. If the line fails you will be dumping fuel inside the car. Very dangerious. Most vintage race cars mounted the fuel pressure gauge near the base of the winshield outside the passanger compartment or under the hood near the pressure regulator.

[Frank H.]

Re: Stewart-Warner Electric Fuel Pump

if you proceed with this you should seriously consider an oil pressure regulated cut off so the pump doesn't continue to run when the engine isn't.

[Gary C.]

Re: Stewart-Warner Electric Fuel Pump

Bob,

Added a relay on the ignition coil hot lead to power the electric fuel pump. Fuel pressure gauge was on the fuel line at the carb and mechanical fuel pump was blocked off.

Gary
....

[Bob B.]

Re: Stewart-Warner Electric Fuel Pump

Thanks to everyone for the great info! I don't have a pic on this computer, but the S-W pump is the Model 240, as Jim surmised. I have a couple of the 12V ones and a 24V one. - Bob