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fuel pump,mechanical or not?

Discussion in 'The Garage' started by shaun89, Jan 22, 2007.

  1. shaun89

    shaun89 1/2 ton status

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    im putting a 400hp 350 with a 770 carb in my truck and i cant decide if i should use a mechanical fuel pump or an inline electrical one. are there any advantages to either?
     
  2. Tominator II

    Tominator II 1/2 ton status

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    You can run both. I do that in 2 trucks. I have a pressure regulator on both trucks also.
     
  3. 1977k5

    1977k5 3/4 ton status Vendor

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    I have an electric fuel pump (Holley blue) and wish I had stuck with the mechanical one. Here's why:

    Its very loud despite my best efforts to quiet it
    Can I find a quick (trail) replacement if it fails?
    Why do you really need an electric pump?



    The stock pump probably would have flowed enough fuel for my truck, I doubt I could actually empty the fuel reservoir in the short time I am ever at WOT.
     
  4. ntsqd

    ntsqd 1/2 ton status

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    I like mechanical pumps, but in a similar thread not long ago I realized one rather large problem with them. Vapor Lock.
    If you put any liquid under a vacuum it boils at a lower temperature. Since mechanical pumps are better at pulling (vacuum) than pushing it stands to reason that you're at a higher risk of vapor lock in the section btwn the tank & the pump.

    A bonus to a rear mounted pump is that it puts the whole supply system under pressure, which raises the boiling point.

    Based on this, my suggestion is to use one of the external TBI pumps even though you're likely carb'd. To do this correctly you'll need to use a regulator, preferably a by-passing one so that you can return fuel to the tank. This also helps with the vapor lock potential problem.

    The reality check is that I've no idea how important preventing vapor lock is in CT. In KA it can be pretty important.
     
  5. dyeager535

    dyeager535 1 ton status Premium Member

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    Vapor lock was not an issue with stock GM vehicles, especially after the inclusion of the fuel return line. If there are issues with vapor lock, it's external of the fuel pump. Might not help a problem when dealing with modifications, but it's not the cause.

    Stick with stock mechanical. Quiet, cheap, reliable, no regulator, incredibly easy to find at any parts store.
     
  6. 1977k5

    1977k5 3/4 ton status Vendor

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    Electric pumps perform very much like mechanical pumps (form a push/pull standpoint). The reason that fuel injected vehicles almost never vapor lock is because almost every fuel injected fuel pump is in the gas tank. Fuel pumps cannot pump vapor, that's what happens when a vehicle vapor locks. If the pump is near the tank, it is very likely to always pump liquid and not vapor lock. Pumps much further forward (eg. engine mounted mechanical pumps) have lots of fuel line before them that gives the fuel a chance to vaporize in hot weather.

    My truck never vapor locked when it had a mechanical pump, even in 100 degree weather.
     
  7. ntsqd

    ntsqd 1/2 ton status

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    Did you read and understand what I wrote? By pressurizing the supply line the boiling point goes up. That is why EFI engines are less prone to vapor lock. Vapor lock doesn't give ratz azz where the pump is or what type it is. No matter what type of pump if the fuel boils off in the line you may get vapor lock. Most EFI injectors are designed for liquid fuels and don't work as well or at all with gaseous fuel.
    Pressurizing the system raises the fuel's boiling temperature just like a radiator cap raises the boiling point of coolant.
    While it's true that both types of pumps do push and pull, for what ever reason electric pumps are better at pushing than pulling, while the reverse is true of mechanical pumps.

    I still like the simple robustness of a mechanical pump. I just wish there was an easy way to put it near the fuel tank.
     
  8. vortec

    vortec 1/2 ton status

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    autozone, and some online shops have a couple of inexpensive out-of-tank inline electric pumps that are made to be used either alone or as booster pumps for mechs. mr. gasket 12s and 42s, i believe. different pressures and/or flow rates between the two models. i don't remember the precise numbers. i've never had bad luck with mr. gasket products, so it may be worth checking out. i've considered it, even though i've never had vapor lock issues, myself.
     
  9. shaun89

    shaun89 1/2 ton status

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    hmm i guess ill go with a mechanical fuel pump, seems simple and no wires...i like that, thanks a lot guys:bow:
     

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