Re: Anybody got the end all cure for vapor locking?

Posted by Tim Cole On 2022/1/7 18:57:04

One area to avoid is sharp bends in the fuel lines. Those fancy 90 degree bends may look great, but they create a Bernoulli effect where a low pressure differential is created the same way as an airplane wing. If you look at the Model A the fuel line looks sort of ghetto, but that is the way Ford reduced those sharp bends.

The vacuum tank next to the exhaust manifold is required for the gravity feed. In 1931 they put the pump up front thinking that would be the coolest place and by 1933 moved it to the opposite side on the Eight cylinder cars, but kept a couple of very sharp bends with fancy fittings going through the frame.

These problems continue today. Tanks now are sealed to maintain pressure with relief valves to prevent excess, and pumps are submerged in the fuel, thus preventing any low pressure spots. But misfire conditions sometimes still exist that are remedied by changing the shape of the fuel lines in some cases. Even in systems running 450 psi.

Today we have great ways to use thermo-couples to look at temperatures along the fuel lines. I think Packard was groping for a solution. With a diaphragm fuel pump the intake valve creates low pressure to draw fuel and if bubbles are being created and merging everything can come to a halt. Testing with clear fuel line is one way to analyze the problem.