I am about to put in a new long block 350 in my 57.
I currently have only an electric fuel pump installed. I plan to put a new mechanical pump in and leave the electric as a supplement to starting.
I will rewire it to use a separate switch under the dash to turn it on and off.
Question- Do I need to plumb in a bypass fuel line at the electric pump to provide an alternate path around the electric pump for normal (pump off) operation?
Those carbs run at 6.5 pounds max pressure. That is not to say that you should run at 6.5 but that is the max. The Carter 4070 has been around for decades and is a good choice. You install it close to the tank, put a filter in line before the pump. These pumps use the fuel to cool the motor internally so you have to keep junk out of it. The design is rotary vane so it does not need to be on all of the time, fuel will pass. Cost is under a hundred. I used a 4070 for years as a primer pump, and for the occasional run down the strip.
What you do want to do is take the time to install the pump using a relay kit. back in the day when we did not know any better we ran the power directly to a switch under the dash. Too much through the switch so use a relay. Second thing is pick up a carter pressure switch. If for whatever reason the motor shuts off, the pump will also shut off.
I still run a carter pump, its wired through a relay and a pressure switch. Works exactly like it should. Turns on when cranking, stays on when running, turns off when the oil pressure drops.
I read these posts and also went back and read the many other ones here on this subject.
My decision is to remove the electric pump that I have and disable the relay and wiring and just go with the mechanical pump.Enough "old salts" on here have convinced me that the original pump setup has been running these cars for decades.
Sort of. With today's fuel, some of the components flash off at much lower temperatures. So for some cars, it makes starting a little harder after sitting for a while which is why they use an electric pump as a temporary primer (push vs the pull of a mechanical pump). Give it a try with out the electric pump and see how it goes. You can always add one later.
A mechanical pump in good working order is far better at suction than an electric pump. An electric pump needs to have a gravity feed to avoid suction problems. If you don't have gravity feed, the electric pump is probably going to be worse, not better.