Dual fuel PFI rails....

[Barry Tisdale]

I understand the single rail, 2 fuels deal.  BUT, like you said, changeover will take a bit of time (WAY too long), plus dilute the two fuels, bit by bit, by the volume contained in the rails.  Common volume is maybe 120ml; would take several seconds to completely clear.

Ok, with 2 rails feeding each injector, there's maybe 2cc or so "common" volume between any rail and the injector.  The fuel pump prevents backflow; otherwise, it wouldn't hold pressure w/ the engine off - no check valve needed there.  Each rail is fed by its own pump, & fuel exits via its own pressure regulator.  Also, each rail 'out' line has a solenoid valve in parallel with the *same* fuel pump; normally closed valves.  SO - when FP#1 is ON, retrun line #1 is also open = normal operation.  Ditto for setup #2 - separate FP, reg, solenoid valve, takk, the works.

Sure, you will get *some* mixing of fuel, but quite minimal, maybe 12cc or so per switchover.  Pump gas is returned to its tank, race gas to its.  Hardly any mixing.  As soon as the electrical switchover takes place, the rail NOT being used is OFF, pressure-tight.  Remember liquids are incompressable; the fuel in the unused rail has *nowhere* to go; will get *slight* mixing @ the interface between the 2 fuels due to turbulence, but again, minimal.

As far as 5/16" being inadequate for rail size, seems to me the vast majority of pressure drop occurs @ the injector inlet - this is 1/8" on mine.  Pressure measured @ the first injector and @ the last (on the rail) should be da** near equal. Inlet fitting on my rail has 3/8" bore, outlet is 5/16" OD tubing.

Thanks for all the feedback; where else can so many people get together for idea-bashing??  Time will tell.  Time to start practicing drilling deep holes.....

Barry - Syclone #26