Rods46,
The max spec was 4.5 psi at the carburetor, according to the old Chevy documentation.
If you would prefer an electric fuel pump, and still running the 6V system, Airtex E8902 or equivalent is a good choice, comes with an inlet fuel filter, and can be plumbed in near the tank.
Airtex E8902 6V Fuel Pump. Output pressure max is 4.5 psi.
If the truck is converted to 12V, the similar pump is Airtex E8251 or equivalent
Airtex E8251 12V Fuel Pump. Again, max output fuel pressure is 4.5psi. To be exactly similar to the 6V pump, an inlet fuel filter can be added (since the 12V model does not come with the filter). Wix P/N 33046 is essentially identical to the filter supplied with the 6V pump, and directly threads into the pump's inlet fitting. If a 5/16" tubing inverse flare fitting is desired at the filter inlet, Wix P/N 33081 may be used instead.
Wix P/N 33046 fuel filter (same as NAPA P/N 3046) is a correct replacement unit for the inlet filter that comes with the 6V pump, also. Or, Wix P/N 33081 (same as NAPA 3081) can be used if a 5/16" inverse flare is desired on the inlet side.
Now, for the safety cutoff and pump installation, Airtex published this 3-minute video several years ago that explains both. The recommended oil pressure cut-off switch is nothing more than a GM three-terminal switch that was used very commonly in the '70's to early '80s on a number of cars and Chevy trucks. The Airtex P/N OS75 that is mentioned in the video crosses over to Delphi FA0004, NAPA Echlin OP6610 or OP6617, or GM P/N 3986857. Here's the video that shows the wiring and pump installation:
Airtex Universal Electric Fuel Pump Installation Video.
There are a couple details in the video that I do not particularly like. The pump installation uses rubber hoses at both sides of the pump. While that will work, an appropriate inverse flare fitting can be used to hardline the outlet side. In that case, I use a simple vibration isolator under the pump. The video also shows Teflon tape used to seal the pipe threads into the pump and for the oil pressure switch and fittings. Teflon tape shedding is an issue if it gets in the fuel system. I prefer to use an ethanol gasoline and oil-compatible sealant like Permatex 56521 (Loctite 565) instead of the tape.
Hope this all helps!
Doug
