Tim asks, "What would be the pros and cons of using a 6v electric fuel pump that delivers 3-4 psi or 5-8 psi?"
This is like choosing between Marlene Dietrich and Marilyn Monroe. One is a raven haired beauty with smarts, the other is a blond headed beauty without a lick of sense. Nonetheless, both are capable of taking care of your needs.
Selection of a fuel pump is based upon demand and delivery; the higher your engine demand, the more a pump needs to deliver. Volume need is first, pressure need is second.
Here is contrast. You have a Chevy 216 with a tiny one barrel, you could use a child's squirt gun to service this engine just fine, even at full throttle. My girl's Corvette has dual quads sitting on top of velocity stacks. She needs a Chevron oil refinery behind her seat to keep enough gasoline flowing just at an idle.
For both an old tiny 216 and her modern 383, I would use a mechanical fuel pump producing 6 pounds of pressure or less, never more than 6 pounds. This hot rod Corvette of ours has a return line running from the carbs back to the fuel tank. A typical Edelbrock mechanical fuel pump delivers more gas to the carbs than what is really needed. Fuel pressure at her carbs is only about four to five pounds which is plenty. Difference is an Edelbrock fuel pump delivers a lot of gas but at a low pressure.
Here are some pros and cons between mechanical and electric pumps.
Both can deliver a high gas flow at a low pressure.
A mechanical pump delivers more gas as engine speed increases. An electric pump delivers the same amount of gas regardless of engine speed.
A mechanical pump has the power of the engine operating the pump. An electric pump has only the power of its internal motor or vibrating solenoid.
A mechanical pump will deliver more gas per pump stroke than will an electric pump.
A mechanical pump "sucks" gas from a tank more powerfully than does an electric pump.
A mechanical pump only quits when the engine quits. An electric pump quits when there is a loss of electricity, such as a blown fuse or internal short.
A mechanical pump will last over half a century. An electric pump lasts about five to ten years.
A mechanical pump is less expensive than an electric pump while all things are equal between the two pumps.
Personally, I only use mechanical pumps, always. A mechanical pump will almost never quit working for you. An electric pump will eventually quit working, without warning.
Billyray
