My factory fuel pump has been failing for the last year or so, and it should cr*p out any time now.

Im running a 750 holley double pumper, its jetted at 70/79 primary and secondary, and will get its PV's replaced with 8.5s. Parts of the part throttle circuit have been modified (drilled larger) to give better accelerator response. The car doesnt see much track time, but the few times ive gone, ive felt the lack of fuel. It wont start knocking or anything, but you can feel its being held back...

I have a holley blue electric fuel pump, but i dont want to install an electric one. Its just more work than i want to do in short.

So im going shopping for a mechanical one. However, im unsure of what i need.

I know the 7psi rule, but what determines if i can go to 9psi or not? Also, should i look at the psi ratings, or the gph rating?

I want the highest gph rating possible, but i dont know how high i can go. It just says that 130gph holley pumps need to be regulated.

Any help appreciated.

 

Sounds like your factory in-tank electric fuel pump is either failing or wasn't operating.

 

The limiting factor in fuel pressure for a carb is how much pressure the float can put on the needle and seat to keep it closed against the fuel pressure. Anything higher than about 6 1/2 PSI and you'll need to regulate it down.

Running a larger pump than you need doesn't gain you anything, other than some power wasted moving around fuel that you don't need. Better to be too large than too small, though.

 

I need to replace the float on my carb anyway (Holley 4779-6) this winter. One of them sank.... I wouldnt mind replacing a needle/seat and float combo to work with each other.

Seems like most people go for the 110gph one, but i honestly dont know what would work best for me. 80gph seems to be the lowest, but although my car is mostly street driven, it is not a stock, or mild engine. So id like the pump to keep up with the carb atleast. I listed the jetting, and PV settings, because after finally tuniing it last summer, it seemed to like those combos the best.

Also, i should have mentioned, i dont use an in tank pump (whether or not its there, i dont know). The pump im referring to is on the block. The engine is a 1975 350. It is definately failing, because it operates at about 3-5 psi.....

 

There's nothing wrong with 3-5 PSI, as long as it delivers enough volume.

 

I dont think it does. I wouldnt be worried if it was atleast consistent. But it changes. So for example, it will go to 4 psi one day, and stay there. Other days it will flicker between 3-5. I dont think ive ever seen it less than 3, but anyways.

I dont really know how to determine the flow, without a meter.

Id like to upgrade, but i dont know which flow rating to go with. Any help with that would be appreciated.

 

That's my point. It was there from the factory. If you didn't remove it and don't run it, it's keeping your poor block-mounted pump from being able to suck through it. Like sucking a milkshake though a coffee stir stick.

 

Oh i c.

I didnt realize the factory pump would even be able to pull fuel through the other pump, so i assumed it had been removed.

How do i get the intank out?