- There are several things in the demo video that don’t replicate a typical return via the filler neck:
1) The person conducting the demonstration holds the return line a few inches above the surface of the fuel (mineral spirits). As a consequence, the high velocity and high volume stream entrains air as it enters the surface of the fuel. This is the exact opposite of what happens when fuel returns via the filler neck. In that configuration, the return fuel stream is a significant distance from the surface of the fuel in the tank, it is entering via a very large opening (the fuel filler) and it is at low velocity. As a consequence, very little air - if any - will be entrained in the return stream.
2) When the person conducting the demonstration aims the return fuel stream with entrained air directly at the pump pickup, the pump rpm changes. Of course it does, he’s intentionally feeding it air under conditions that don’t exist in your fuel tank. The fuel return and fuel pickup in your Lotus are not 3” apart as in the demo.
3) The highest fuel return rate will be at idle, where entrained air is not a big deal (if it existed). At high throttle settings when you want maximum power, fuel return and the potential for aeration is minimized.
My guess is that any aeration would be largely attributable to fuel sloshing in the tank as a result of vehicle motion, not fuel return.
My Porsche returns fuel via the filler neck and my VW dumps it at the top of the tank . . . I’ve never experienced any fuel-injection problems, including at idle where the inability of the fuel system to deliver fuel at a constant volume and pressure would result in an erratic idle (especially in the VW, which has a very crude second-gen fuel injection system). One other related data point . . . I have designed and built lots of fuel systems for 1/4 scale RC aircraft that use gasoline and pump systems. The engines are extremely
sensitive to pressure or volume changes. Despite that, I’ve never had a problem returning fuel to the top of the tank.
So unless you are actually experiencing problems related to foaming fuel, I doubt you need to “fix” this. A header tank to ensure fuel delivery during prolonged turns, of course, is a totally different problem and solution. But if there was any aeration, the header tank would likely remove almost all of it.