Fuel System Revisions
It has been more than four years since we upgraded the GT as chronicled on this blog. The GT has not been driven much between Ryan’s employment working on the current Ford GT and my preoccupation with building and flying the Carbon Cub. With the airplane complete there is more time to attend to the GT. Driving it more, I have been bothered by a persistent but intermittent fuel delivery problem. This was mentioned in a post in May 2013, noting the Holly HP-125 pumps would seem to lose their prime and the pressure at the regulator would seem to fluctuate. On occasion the engine would just die due to fuel starvation.
The Holly fuel pumps were installed with the input about six to twelve inches above the level of the fuel, depending upon how full the tanks were. With no resistance on the output side this was not a problem. But with a regulator set at less than three pounds pressure the pumps often have a hard time priming. Holly specifically states that the pump should be installed at or below the pickup level, so it is not a fault of the pumps, per se. With a regular set at seven pounds pressure for a four barrel carburetor they worked fine. But with the Weber IDAs set at two pounds this was a problem.
Facet makes a pump specifically designed to pull from a fuel tank well below the level of the pump. One specific model is rated at 50 GPM and will pull from 50 inches. (Pegasus part number FAC-40290). It comes with an integrated fuel filter on the input side and a check valve. Output pressure is more than adequate. It is approximately the same size as the Holley pumps.
We did a test installation and immediately discovered two things. First, they are LOUD. But with straight exhausts should not be an issue. Second, the pressure immediately came up to 3 pounds without fanfare, and stayed there several minutes even when the pump was off, confirming that the check valve worked. So on to the final installation.