From Rick:
"
I have never tryed to run both a electric fuel pump and mechanical together in the same car. I ran one or the other never both. I was afraid of too much fuel pressure for a carb setup or too much pressure build up between the electric and mechanical. Some one else here my be running this way. Not Sure??"
That would be me.
When the Sideoiler of about 550HP and quads went in (in '91), it had a mechanical pump only. I installed an Autometer in-car fuel pressure gauge (plumbs
antifreeze to gauge, not gas) and had a steady 6-6.5 fuel pressure up to about 5000-5500RPM. From there to 6800, pressure sank to near 4.5 PSI-not what the motor wanted.
I then added a switched Holley Red which is a 7PSI max feeding the Carter. A steady 6.5 to 7PSI under all conditions. Didn't blow the needle valves off, no flooding, no ill affects. No need for regulator or exotic jillion GPM pumps. Much easier hot
and cold starting with no wasted cranking. Track MPH improved by 4 or 5. And it's deadheaded-no return plumbing. Admittedly, this is a different engine combination then the OP is using. Only stating what works for me.
I notice many guys wanting Pro Stock fuel systems to feed only 600HP combinations-needless expense and complication.
The key is to use just enough 'component' to feed the ideal carb fuel pressure of 6.5 or 7.(aggressive cam / big cubes -smaller engines and lower RPM are fine at 5.5 and Webers only want around 4!) Ride around with a pressure gauge in the cockpit and it will speak volumes.
To answer Wbulk, with the electric switched off, the Carter will pull fuel for only a short time through the Holley. The motor will then stall.
I removed the Holley last year for the first time in 17 for inspection. No debris inside, the gears were in as-new condition. Lightly lubed with assembly lube, safety-wired the base plate and reinstalled. And this is the cheapest electric Holley makes.