SBC mechanical fuel pumps

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carnutjw

G-Body Guru
Sep 17, 2017
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I'm pretty sure the fuel pump on the 305 in my Cutlass is the original, still running a Q-jet. Heading out on Power Tour (in August) so I'm considering changing it or at least taking a spare. I've looked through previous posts and diagrams of fuel pumps, and now have some questions. Carter lists the M6624 for stock replacement, and M4685 with same external dimensions(thread sizes, lines,etc.) Airtex has similar products and specs. As I understand it, typically in fluid transfer higher volume means higher pressure and visa versa if nothing else changes, but.........
M6624 has 9 psi max pressure and 23 gph max flow.
M4685 has 7 psi max pressure and 40 gph max flow.
1) Am i correct in the assumption that the max pressure would be a function of the diaphragm return spring (it wouldn't return to pump more fuel the next stroke if pressure was too high) and the flow rate is controlled by an internal orifice size to the outlet?

2)With most people saying 5 psi max on a Q-jet, why would GM increase the fuel pressure over older versions? New float design, float level setting lowered for emissions, ??? I understand those are max numbers from Carter, probably lower during most running conditions.

3) Has anyone RECENTLY bought a stock replacement or similar mechanical fuel pump for a SBC that wasn't made in China and if so where?

Thanks guys for entertaining my curiosity.
 

TURNA

Rocket Powered Basset Hound
Jul 24, 2009
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The factory replacement Carters are made in Korea

I just bought one for my Olds

The "High Performance" Carters are made in USA
 
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TURNA

Rocket Powered Basset Hound
Jul 24, 2009
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Socialist NY
Also according to Carters website both pumps are 4-6 psi

Whats the difference then........know idea
 

565bbchevy

Geezer
Aug 8, 2011
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Also according to Carters website both pumps are 4-6 psi
Whats the difference then........know idea
Probably GPH
 
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