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Another forum member posted a WTB ad looking for a specific # AC fuel pump, so I went to look at mine. It says LH 40709 on it. Came off my 1971 LT1. Since the car sat for 10 years, and I don’t care about originality, I plan to put a new pump in. What I’m wondering is if the “L” is specific to the LT1 and if so, what is different about it? What I mean is, if I just buy a pump for a standard 350 would it work or was this model made to maybe pump a little more than say a base 350 would have in 1971? I want to know if I buy a fuel pump that says it works on a 1971 350 would I be good to go?
Last edited by litevette; Aug 29, 2025 at 09:53 AM.
Another forum member posted a WTB ad looking for a specific # AC fuel pump, so I went to look at mine. It says LH 40709 on it. Came off my 1971 LT1. Since the car sat for 10 years, and I don’t care about originality, I plan to put a new pump in. What I’m wondering is if the “L” is specific to the LT1 and if so, what is different about it? What I mean is, if I just buy a pump for a standard 350 would it work or was this model made to maybe pump a little more than say a base 350 would have in 1971? I want to know if I buy a fuel pump that says it works on a 1971 350 would I be good to go?
No, the L isn't referring to an LT-1. Current belief is that crimped-style pumps have a 2-letter code before the pump number (40709) where the first letter is the month and second letter the year. The months begin in January with A, Feb = B, March = C, etc.; the years are 1966=F, '67=G, '68=H, '69=I, '70=J. For '71, the coding changed to a Julian and year code. This pump should be December '68.
Not just any '71 SB spec'd pump will work for you. The differences between the various pumps are the inlet/outlet locations and connection angles and whether there is a return port or not. If your pump above aligns everything as needed, match up a new pump to do the same. The pumping volume needed is basically the same for all engines, ~5-7psi.
New pumps seem to put out a lot more than this (~10-12psi) so be aware of any over-pressure symptoms after installation. I put a new Carter on my 427/Holley and the carb leaked at the pressed plug where the fuel inlet is located. Had no leaks before using the original pump, so I believe this pump is over-pressurizing the fuel delivery.
Last edited by barkingrats; Aug 29, 2025 at 01:49 PM.
Thank you and Thank you @barkingrats !
Good info for sure. Yes, I was going to pay attention to the outlet/inlet orientation as there's no return. I know others had a return. I do plan to run a pressure regulator. I have read about the new pumps running to high and causing maladies at the carb. Thanks again for the reply and info provided!
General rule of thumb for sizing your fuel pump is .1gph per hp you’re making at the crank.
Never have been exposed to that rule of thumb. Thanks! How would I calculate that? I took the 330 hp that a 1971 LT1 was rated at, multiplied it by .1 and it came to 33. I know that would not be a good psi rate, so what am I missing here? How do I convert those known #’s to psi? I do intend to run a pressure regulator, so what would you set it at knowing that 330hp is the baseline? Thanks in advance for that info!
Not knowing that, I intended to start at 5 psi, as I’ve heard thats a good base, do my tuning (carb, ignition) then push it up as needed, backing off if over fueling issues presented themselves. Would be curious to know what the actual psi output is on the stock pump is on a good running 1971 Lt1. Other than HEI, headers later on and modern plugs, pretty much no performance upgrades planned. Freeing up/relieving only a possible few ponies with only the headers and an electric fan. Based on my limited knowledge there’s nothing in that mix that would call for a psi or gph increase in the pump, but am very open to learning better ways that equal better results.
Last edited by litevette; Aug 30, 2025 at 12:32 AM.
Yes you’re on the right track, 330hp, about 33gph. It’s hard to find flow under pressure charts, most of the time manufacturers just list free flow numbers. A stock fuel pump is like 40-45gph free flow so it’ll cover 33 under pressure.
As far as what pressure to set it to, that’s up to your carb. For a Qjet I have zero idea, I’ve never run them. But for a Holley DP, I set it to 6-6.5#, edelbrocks, 5-5.5#
Curious About This Fuel Pump
