Selecting a Fuel Pump for your Blowthrough Setup

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I decided to write this tech article because of all the confusion out there regarding fuel pumps and how to go about selecting one for your blowthrough project. It was originally posted over at TurboMustangs.com in the Carbureted Tech Forum. You must do a little math, but it will take the guesswork out of selecting a pump. In order to calculate your pump needs, you'll need to know two basic things: how much pressure will your setup will need, and how much Horsepower you plan on making.

    First, you'll need to calculate how much pressure you need. You'll need to know a few things first: 1) Max boost you plan on running, and 2) Regulator type. Why does the regulator type matter? Because if you are using a dead-head style regulator, you must have an additional pressure differential across the regulating orifice to be able to control fuel pressure. Generally, this will need to be 10-15 psi. If you’re running a bypass or return style regulator, you will not need this extra pressure, because the regulating orifice is on the return side of the system. There will also be losses in the system from fuel lines and fittings, as well as acceleration losses. You’ll need more pressure at the pump to account for these losses. You can generally assume these losses to be around 5 psi. If there are a lot of bends in the system, your losses may be more. With these things in mind, let’s calculate how much pressure we need.

    P = (base fuel pressure) + (boost pressure) + (line losses) + (10-15 psi if running a dead head regulator)

So, for a blowthrough engine with a bypass regulator making 20 psi boost and a base fuel pressure of 7 psi we have:

    P = 7psi + 20psi + 5psi = 32 psi

    If we ran a dead-head regulator, we would need 10-15 psi more than that to have adjustability at the regulator. So if we run a bypass regulator, we’ll need 32 psi and if we run a dead-head regulator, we’ll need at least 42 psi. Now lets figure out how much fuel flow we’ll need.

    How much fuel we need will be dictated by how much Horsepower we plan on making. In our case, lets say we are shooting for an even 1000 Hp. This number needs to be the Hp at the crank. At this point, I need to introduce some IC engine fundamentals. Every engine has what is called a BSFC, or Brake Specific Fuel Consumption. This number is the amount of fuel it takes, in pounds, to support 1 Hp for 1 Hour. The units for this number is (lbs/hr)/Hp. For a naturally aspirated engine, the BSFC will be around .45-.55 (lbs/hr)/Hp. For a turbocharged engine it will be around .55-.6 (lbs/hr)/Hp. A supercharged engine will be around .6-.65 (lbs/hr)/Hp because of the added Hp it takes to spin the supercharger.

    To determine how much flow we need, we simply take our target Horsepower and multiply it by the corresponding BSFC. I generally use the high end of the scale just to get a conservative estimate. So, for our 1000 Hp turbocharged engine we have:

    Fuel required = (target Hp) * (BSFC)

    Fuel required = 1000 Hp * .6 (lbs/hr)/Hp = 600 lbs/hr

Note: Many fuel injection pumps use lbs/hr as a measure of flow. If you want to know the flow in gal/hr, simply divide the lbs/hr figure by 6, since gasoline weighs about 6 lbs/gal.

    At this point, we need a pump that flows 600 lbs/hr (or 100 gal/hr) at 32 psi with a return style regulator or a minimum of 42 psi with a dead-head regulator. Now we need to start looking at fuel pump performance curves to see what they flow at specific pressures. For example, If you look at the flow curve for the Aeromotive A1000 pump below, we can see that at 32 psi the pump flows ~600 lbs/hr at +12V. This pump would work on a system with a bypass regulator. However, at 42 psi, the pump only flows ~550 lbs/hr, which is not quite enough at +12V for a dead-head setup. The pump will work for either system at +13.5V, but you would need to be sure the pump was running at 13.5 volts at WOT, which may not be possible if you’re running a lot of electrical accessories, like electric fans, electric water pump, fuel pumps, etc. It’s best to err on the side of caution with fuel systems, so if you were to run a dead-head regulator, a larger pump would be in order. 

Graph courtesy of Aeromotive, Inc.

Depending upon your Horsepower needs, there are a number of pumps out there that will work for your particular blowthough setup. All you need is a pump performance curve and a little math.

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