WS6 TA

When most people start seeing signs of fuel delivery problems they start throwing bigger pumps, fuel lines and injectors at the problem. There just doesn’t seem to be much information about what happens at the rails which makes throwing big race pumps and a stack of braded lines at the problem the easiest, sort of brute force solution.

5.0 fords are a great example of this with their absolutely tiny stock fuel rails and I’ve run across a few instances where the engines show fuel delivery problems with monster fuel systems and stock rails, and where what would normally be considered basically undersized fuel systems proved fine with what would normally be considered oversized rails.

Secondly, newer cars typically have deadheaded fuel rails without returns, which I’m guessing was done mostly to prevent tampering, but in a way seems like a real advantage (not returning hot gas to the tank…), but I wonder what affect that has on fuel rail size and other delivery issues. On our project cars this can be done like the factory does it (PWM to the fuel pump) or using an aftermarket regulator with the rails branched off the inlet side of the regulator.

So does anyone have an idea about optimum, minimum or some way of predicting fuel rail sizing, what affect cross section has vs total volume and or what affect deadheading the rails has on this vs the more traditional flow through setup?

It’s interesting to note that it doesn’t seem that OEM’s agree here either, just looking at the dramatic differences in sizing for similar applications between the OEMs. FWIW, though this is mostly a question about theory, it does have a practical side, I have a bunch of -6 fuel rail stock and am debating if I’m going to use it or order some -8 or -10 for a single plane/fi conversion that I’m working on.

AdioSS

it would seem to me that larger fuel rails would have less of a pressure drop as each injector fires meaning a more equal distribution of fuel.

96capricemgr

What application are you talking about? My understanding is that the LS1 rails are easier to max out than the LT1 rails. One of the most powerful LTx setups I know of runs stock rails plumbed parallel rather than in series. 4400lbs propelled to 146mph in the 1/4 says there is a lot of HP there.

The stock fuel line ID is also deceptively large when compared to AN stuff.

The OEM deadhead systems are about cost, they save 15 feet of return line and a fitting into the fuel tank. Some of those deahead systems are quite troublesome even vaporizing the gas in the line at the far end of the rail, the few ounces in the rail heat up a lot faster and a lot hotter than the whole tank of fuel will.