Quote:
Originally Posted by Jay S
I don’t think the “momentary” fuel switch will work very well. It takes to long for the pump to build pressure and purge the air out. It will get behind. Even my Walbro in tank carb set up takes a considerable amount of time time when it is first turned on to fill the carb. Longer anyway than a EFI set up, the lower pressure 7 psi doesn’t force they air out nearly as fast as 40 plus psi EFI set up.
Those diaphram pumps like the ACDelco and Mr Gasket are usually rated at 30 gph at operating pressure. I don’t know what the pressure and volume performance curves look like on those. My feeling is the mechanical pumps is doing most all the full throttle work if those pumps are feeding a mechanical pump. But I could be wrong, since I have never seen the performance chart. By itself 30 gph would only be good for 300 HP.
The Carter M6122 mechanical pump is rate for 40 GPH at pressure. Free flow is 120 gph.
The free flow of the Carter vane pumps is not published, but rated at 50 gph at pressure. My guess is it is about 100 gph free flow.
The Holley street pumps have higher ratings, but are rated differently than Carter. Not all that accurate in my opinion. The flow drops a lot with head pressure at the outlet, I think they run closer to 70 gph at a normal carb operating pressure. Just a guess though. Better than the Carter, not as good a 140 Mallory.
The idea of the pumps in series, both pumps do some of the work. The electric pump becomes a charge pump for the mechanical pump. Each pump has less losses. They operate at lower pressure on their performance curves. Not bullet proof for drag racing, but an improvement over a single pump that does not pull from a sump or a in-tank setup.
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All makes sense but still curious about the pressure at carb inlet if both pumps are operating. I guess I'm asking what the pump curves are by themselves and in series. To me, if an electric pump puts out only 7 psi, it will still add to the pressure built by the mechanical pump and end up maybe too high for a carb needle and seat.
"both pumps doing some of the work" makes sense to me from a flow perspective but without flow, wouldn't the pressure be roughly additive from tank (0 or atmosphere) to carb inlet?
Mike