Difference: High Pressure vs High Volume Fuel Pumps

Discussion in '1979 - 1995 (Fox, SN95.0, & 2.3L) -General/Talk-' started by No.11, Sep 28, 2011.

  1. What is the difference between the two? I've read a little bit about people saying the high pressure is better for forced induction. But will a high volume not work with forced induction? This ad for the BBK (Walbro) 255 high volume pump claims that

    Does this mean both HP and HV?

    So, let's say I have a car with basic hci and exhaust etc, I put in a 255 high volume pump, will I regret it in the future if I want to add a supercharger? Or can I adjust the pressure with the AFPR to catch up to the performance of the high pressure pump?

    Or, if I just put in a high pressure pump, will it give me trouble being N/A? I heard of people having trouble getting pressure under 40 psi with the high pressure pump.

  2. they're both the same in volume at normal fuel pressures.

    increased fuel pressure is a requirement for forced induction in order to maintain the same pressure differential across the fuel injectors, which keeps the amount of fuel injected the same for a given duty cycle.

    With regard to the difference in pumps, it's a relatively minor difference in my opinion. When you increase fuel pressure, it decreases the volume that is pumped by the fuel pump - that's true with any pump. High pressure pumps are designed not to lose as much volume as fuel pressure increases.

    You can absolutely run a blower or turbos in the future with a normal high volume pump. You will still be able to push enough fuel.

    Here are some numbers for you:

    On a 12V system:
    fuel...regular 255LPH............high pressure 255LPH

    As you can see from the above, they flow close to the same at 40psi of fuel pressure, 58 and 59 gal/hr respectively. If that's your base fuel pressure and you add 20 psi of boost (too much for pump gas), they both decrease in performance to 49 and 51 respectively. That's about a 4% difference in flow, and might make a 20hp difference in a forced induction application at that pressure if you've maxed out both pumps. Keep in mind that you're talking about making over 500hp at this point.
  3. Thank you, this is exactly the type of answer I wanted to hear, very thorough! Just one more question. Any truth to the thing about having trouble getting psi under 40 with the high pressure and therefore not being a good choice on a N/A car? is this not an issue with a kirban afpr?
  4. Absolutely not true. Any adjustable fuel pressure regulator will be able to bring the fuel pressure down below 40 without issue.
  5. got it. one more. can adding a t Rex in line fuel pump make up for the lak of performance of a high volume at higher psi?
  6. I make WELL OVER 500 crank HP in a supercharged application.

    I run a standard volume intank 255L Walbro fuel pump
    Stock non-adjustable fuel regulator
    42 lb/hr injectors
    stock fuel rail
    stock fuel lines
    Kenne Bell Boost-A-Pump (pump line voltage regulator)

    The only reason to run a high pressure in-tank pump is if you're planning on running an FMU in order to increase pressures for undersized fuel injectors.

    I am not a fan of inline, "helper" pumps. If you get into the HP territory where you need an in-line pump (to help you heat the gas :shrug: /sarcasm ) then you should have your sumped tank with external fuel pump all mapped out with AN fittings and fuel lines going to your larger after market fuel rails and adjustable regulator.

    The only internal Walboros that you really need to be concerned about are the 190L (?) pumps. They have a habit of internally by-passing @ 60 (roughly) lbs of internal pressure. Again... not a problem unless you're trying to ramp up pressure to make up for undersized fuel components.
  7. I have no personal experience with the T-rex, but have always heard good things. Hopefully, someone else will chime in.

    I wouldn't worry about it until you start having fuel issues with the 255, though. At that level, you're going to need more than an extra pump. You're talking fuel lines, rails, and injectors soon after you run out of pump + a voltage regulator like the boost a pump.

    Here's some reading for you on another product that might interest you. If you read and understand the first two, I probably won't be able to answer any remaining questions you have:
    Kenne Bell's Boost-A-Pump
    Kenne Bell Boost-A-Pump
  8. Or if you're going to run over 20psig boost from a blower or turbo.:nice:
  9. Tru-dat. :)
  10. FastDriver and Noobz have pretty much covered the bases, so I won't beat a dead horse there.

    I do want to toss in the new Aeromotive 340 lph in-tank pump, just for discussion purposes. That's a serious unit, I'm glad the aftermarket finally came up with a high horsepower pump that utilizes a stock-like fuel system setup (though I don't know if you can get away with stock fuel lines/rails/regulator on that one). Chris, you know anything about the 340?

    Aeromotive | 11140 - 340 Stealth Fuel Pump (Center Inlet)
  11. All I know is i have fuel issues with my setup, and im pissed! I dont want to spend 2 grand on a fuel system when Im so close to being done with this car anyways. Then again only beng able to rev to 5500 rpm sucks!
  12. Copied from the FORD RACING PERFORMANCE PARTS catalog:
    Fuel Pumps
    The following information is presented assuming the above information has been taken into consideration regarding BSFC, fuel pressure and specific gravity of the fuel being used. Most fuel pumps for electronic fuel injection are rated for flow at 12 volts @ 40 PSI. Most vehicle charging systems operate anywhere from 13.2v to 14.4v. The more voltage you feed a pump, the faster it spins which, obviously, will put out more fuel. Rating a fuel pump at 12 volts then, should offer a fairly conservative fuel flow rating allowing you to safely determine the pump’s ability to supply an adequate amount of fuel for a particular application.

    As previously mentioned, engines actually require a certain WEIGHT of fuel, NOT a certain VOLUME of fuel per horsepower. This can offer a bit of confusion since most fuel pumps are rated by volume, and not by weight. To determine the proper fuel pump required, a few mathematical conversions will need to be performed using the following information. There are 3.785 liters in 1 US Gallon. 1 gallon of gasoline (.72 specific gravity @ 65° F) weighs 6.009 LBS.

    To be certain that the fuel pump is not run to its very limit, which could potentially be dangerous to the engine, multiply the final output of the fuel pump by 0.9 to determine the capacity of the fuel pump at 90% output. This should offer plenty of ‘cushion’ as to the overall “horsepower capacity” of the fuel pump.

    To determine the overall capacity of a fuel pump rated in liters, use the additional following conversions:
    (Liters per Hour) / 3.785 = Gallons
    Multiply by 6.009 = LBS/HR
    Multiply by 0.9 = Capacity at 90%
    Divide by BSFC = Horsepower Capacity

    So for a 110 LPH fuel pump:
    110 / 3.785 = 29.06 Gallons
    29.06 x 6.009 = 174.62 LBS/HR
    174.62 x 0.9 = 157 LBS/HR @ 90% Capacity
    157 / 0.5 = 314 HP safe naturally aspirated “Horsepower Capacity”

    Safe “Horsepower Capacity” @ 40 PSI with 12 Volts
    60 Liter Pump = 95 LB/HR X .9 = 86 LB/HR, Safe for 170 naturally aspirated Horsepower
    88 Liter Pump = 140 LB/HR X .9 = 126 LB/HR, Safe for 250 naturally aspirated Horsepower
    110 Liter Pump = 175 LB/HR X .9 = 157 LB/HR, Safe for 315 naturally aspirated Horsepower
    155 Liter Pump = 246 LB/HR X .9 = 221 LB/HR, Safe for 440 naturally aspirated Horsepower
    190 Liter Pump = 302 LB/HR X .9 = 271 LB/HR, Safe for 540 naturally aspirated Horsepower
    255 Liter Pump = 405 LB/HR X .9 = 364 LB/HR, Safe for 700 naturally aspirated Horsepower

    Note: For forced induction engines, the above power levels will be reduced because as the pressure required by the pump increases, the flow decreases. In order to do proper fuel pump sizing, a fuel pump map is required, which shows flow rate versus delivery pressure.

    That is, a 255 liter per hour pump at 40 PSI may only supply 200 liters per hour at 58 PSI (40 PSI plus 18 lbs of boost). Additionally, if you use a fuel line that is not large enough, this can result in decreased fuel volume due to the pressure drop across the fuel feed line: 255 LPH at the pump may only result in 225 LPH at the fuel rail.
  13. Forced induction is a double-whammy, so to speak, because in addition to increased fuel pressures, which reduces pump flow, the engine is inherently less efficient. In the formulas above, the BSFC for a turbo motor might be in the .60-.7 range and a supercharger in the .65-.75 range. This can be determined on with proper equipment (data logging).

    I don't know anything about that pump, Nik. I noticed it a few months ago for the first time - same size and all as a 255LPH. However, I've never seen or heard of one used.

    Kdubs, I think you should take a look at the kennebelle boost-a-pump, too. You're very close, and it would put you over, the top. They make a 40amp unit that you can use to run both of your pumps. Or, you can make the power you need to with a single pump in the tank and a single KB BAP.
  14. That was a long and interesting read! I should probably re-read it though when I'm not sleepy as hell, and should probably re-read it again after that because I probably still won't fully comprehend everything, hehehe...

    I did read in there that having a bigger pump with the return style system and a car that's not using all the fuel being supplied by the pump can be a bad thing because of the pump heating up the fuel (boiling point 95 degrees really??? I thought somewhere in the 400s...). Never seen any complaints about that, though. Guessing it's not a big issue in our case.