Correct fuel pump for 65 300 horse

[Daron S.]

OK guys, here goes: I have a 65 Vette new to me. It is a 250HP original block in the car but previous owner rebuilt it with all the correct 300HP components, intake and carb, exhaust manifold and full exhaust. With quality internal parts and balancing it likely over 300 HP. I had it at a local shop for a full fluid service since it has had limited use lately. First issue was we noticed a weeping fuel pump so mechanic replaced it. It did have two incidents of what felt like fuel starvation with me once and mechanic once. I pulled the GF90 fuel filter thinking I would find lots of crud in it since previous owner could only get ethanol fuel but it had little debris and I could blow through it. The car came to me with an AC Delco 40083 which is considered the fuel pump for 350HP and up cars.. My mechanic referred to this pump as a high flow and purchased a AC Delco high flow (per his receipt) replacement pump. It failed in 50 miles. A replacement to that failed in 30 miles. He is getting these locally not from a reputable vintage parts supplier so my concern is the quality of parts he gets and his concern is the engine has some modification when rebuilt like the cam that drives the pump is wrong. The 40083 he took out was in the car for 5500 miles per previous owner so I lean towards my claim of parts quality. So the clarification I need from you is do I go back to the AC Delco part which is described as 250/300 HP compatible or a 40083 high capacity AC Delco. the inlet and outlet are at different places when comparing these two pumps as I understand and the 40083 we removed has them at 180 of each other on the pump housing. If your advice is to use the proper part number pump for a 65 250/300 horse and deal with correcting fuel lines to pump I will take that advice. And does the correct 65 300 horse carb have an accelerator pump diaphragm that could need replacing due to previous owner running a diet of Ethanol fuel and limited use.
I can get Ethanol free here.
Thanks Daron

[Bob R.]

Re: Correct fuel pump for 65 300 horse

In 63 there was only one fuel pump used for all engines (250, 300, 340, 360) (4657) so I think the original pump could keep up with the needs of the engine. I had my original pump rebuilt and they used materials that can handle ethanol fuels and I have never had a problem with it.

[Timothy B.]

Re: Correct fuel pump for 65 300 horse

Darin,

My suggestion would be to use the original style AC 4657 pump that was installed for both the 250-300hp engines. If your engine has the 300hp parts use the 300hp fuel line set up. The pump should provide plenty of fuel for your engine and if it's running ok now there is no need to worry about the ethonal fuel with the accelerator pump.

[Mike E.]

Re: Correct fuel pump for 65 300 horse

In 63 there was only one fuel pump used for all engines (250, 300, 340, 360) (4657) so I think the original pump could keep up with the needs of the engine. I had my original pump rebuilt and they used materials that can handle ethanol fuels and I have never had a problem with it.

My guess is that GM figured out that there was a problem, thus the addition of the 40083 pump in 65.

[Frank D.]

Re: Correct fuel pump for 65 300 horse

Darin,

My suggestion would be to use the original style AC 4657 pump that was installed for both the 250-300hp engines. If your engine has the 300hp parts use the 300hp fuel line set up. The pump should provide plenty of fuel for your engine and if it's running ok now there is no need to worry about the ethonal fuel with the accelerator pump.

I agree There is one Paragon rebuild kit for standard pressure fuel pumps from '56-'66 -

https://www.paragoncorvette.com/p-352989-fuel-pump-rebuild-kit.aspx

They are easy to rebuild - no need to send them off to somebody...I just did one and will soon do another, both original 63 4657 pumps...

[Chris D.]

Re: Correct fuel pump for 65 300 horse

Daron,
The AFB I presume is being used to mimic the 300 HP engine does not work well with fuel pressure over 5 psi. So best to use the regular pressure pump and save the high pressure pump for the next build that uses a Holley.

[Daron S.]

Re: Correct fuel pump for 65 300 horse

Daron,
The AFB I presume is being used to mimic the 300 HP engine does not work well with fuel pressure over 5 psi. So best to use the regular pressure pump and save the high pressure pump for the next build that uses a Holley.

Just circling back to give an update and thank you guys for chiming in. I ordered a correct 300 horse pump and replaced the fuel filter and inspected carb for trash. What we thought was another failed 40083 pump was in fact not broken and mechanic says possible vapor lock in the Carter AFB ( bucking and stalling, not gentle fuel starvation) that he says most folks changed out years ago. So his long test ride and my 6 mile drive home had it running well. So far, so good.
Always open to more input!

Daron