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Fuel Pump Shootout - Fueling for Power

Numbers don't lie

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Part 1: Dyno Testing Fuel Pumps

A fuel pump is the heart and soul of any car so when the time has finally arrived to build a high-horsepower car, why do so many automotive enthusiasts overlook upgrading such an important part? It's good to point out when building a high-horsepower vehicle, the fuel injectors can only flow as much as your fuel pump can deliver. Not only do fuel pumps provide the fuel to the engine, they must provide it in sufficient quantities to enable the injectors to atomize and inject a steady stream into the intake, enabling a proper air/fuel mixture to combust in the cylinders. The factory fuel pump often becomes grossly inadequate to provide fuel to a heavily modified engine. Case in point the many Hondas/Acuras with aftermarket turbo kits still using the original factory pump. The factory Honda pump is a reliable and economical unit for the average 140hp daily driven vehicle, but when the car is turbocharged a multitude of factors must be addressed. The most important would be the larger demand of fuel consumption.

RC Engineering Dynamometer

We randomly selected and dyno tested over a dozen of the most popular fuel pumps available within the tuner market and took a trip to RC Engineering located in Torrance, CA, to strap onto their custom dynamometer. We pushed each pump to their maximum potential using settings ranging from 35 to 100 psi, respectively. With their fuel pump dynamometer, testing your old or new fuel pump eliminates the need to speculate if your unit is capable of delivering adequate fuel flow at specified pressures and variable voltages. RC's custom-built fuel pump dynamometer can test all aspects of a fuel pump, ranging from the maximum flow capacity, psi, fuel temperature, pounds per hour, liters per hour, cc's per minute, amperage, and brake horsepower (bhp) the pump can efficiently support. For testing purposes we took note that the average density of gasoline which is 690 to 760 gph (or 5.76 to 6.34 pounds per gallon). Using calibration fluid rather than standard gasoline allowed us to safely test each fuel pump with accuracy as the calibration fluid was rated at 0.76 S/G and has the same consistency as your typical gasoline found at the local pump. Testing was performed at an atmospheric temperature of 76 degrees F. Before we present the final results of each of the pumps tested, we thought a basic rundown of fuel pump factoids would be beneficial to all our readers.

Calculating Proper Fuel Requirements

Using the proper formula to determine how much fuel your fuel pump needs to support is crucial when building a high-horsepower vehicle. Putting into account variables such as engine displacement, compression ratio, and boost pressures, the final engine horsepower will either increase or decrease depending on the fuel pump's capabilities and whether the proper air/fuel ratio is maintained throughout the entire powerband. Although bhp and flow is increased with most of the testing done, it is not recommended to keep fuel pumps at high voltage if the car is used on a daily basis. The voltage increase will add more wear and tear to the pump's internals and shorten its life significantly.

To make horsepower, your engine will consume a certain amount of fuel. That amount is referred to as the Brake Specific Fuel Consumption, or BSFC. First we need to determine the BSFC. BSFC is how much fuel an engine needs to make "x" amount of power. The lower the number the more efficient the injectors. The BSFC varies, depending if the car is naturally aspirated or turbocharged. For n/a cars the BSFC will be anywhere from .45 to .50. This means the engine will use .50 pound of fuel per hour for each horsepower it produces. For turbocharged engines the scale will be at .55 to .60 lb/hr or higher depending on whether the engine is running on pump gas or race fuel. If the car is running race fuel the BSFC is slightly lower.

As an example, say we use an n/a vehicle rated at 200 hp to the crankshaft implementing the BSFC formula of 0.50 in our formula. Take the 200 hp and multiply by 0.50, the engine requires approximately 100 pounds of fuel per hour (200 x .50 = 100 lph). For a turbocharged engine that makes 400 hp, we use a BSFC of 0.60 to conclude a pump that must flow a minimum of 240 pounds of fuel per hour (400 x .60 = 240 lph). In converting pounds per hour to liters per hour, multiply lb/hr by .6. (For testing purposes and graphing of our dyno sheets at RC Engineering we multiplied the formula using .6309 to average out the means.)

Bypass (Relief) Valve

When pressure at the discharge point exceeds the pump's pressure point, a built-in bypass (relief) valve gradually opens to reduce pressure inside the pump, eliminating damage to the pump. During the testing, we took into observation when the bypass valve fully opened to give readers an understanding of the flow characteristics and limits of each pump. Keep in mind that opening of the bypass is used as a safety feature on each pump and no means the limit of any particular unit. Graph Note: XX indicates pressure valve did not open during testing at 100 psi.

Walbro 255-lph Fuel Pump vs. Knockoff

If imitation is the best form of flattery, we should chalk one up for our Internet friends selling this Walbro 255 knockoff fuel pump. Why consider this a knockoff pump, you ask? Maybe it's the blatant part number etched onto the housing, minus the Walbro sign that's a dead giveaway. The Walbro 255-lph high pressure in-tank fuel pump for forced induction proved to outflow the knockoff fuel pump we purchased online as dyno charts revealed a 18 lb/hr and 11.35 liters per hour flow difference at 45 psi. Up until 80 psi, the Walbro pump outperformed the knockoff unit in every category, but things changed once we reached the 80-psi market. At 80 psi the knockoff pump outflowed the Walbro pump by the slightest of margins. We attributed the performance gains due to the modified bypass valve on the knockoff unit, which offered a higher fuel pressure buildup from 85 to 100 psi. "Don't be too impressed with the higher output numbers as this fuel pumps voltage output was very inconsistent on the dynamometer. It was very difficult to keep the flow numbers consistent at specific psi levels. This is typical with interior pumps sold on the market today. Take into account what types of internal gearing and material is being used on the cheaper knockoff pumps and you'll come to appreciate paying a bit more for quality products," says John Park, RC Engineering fuel injection specialist.

Make: Walbro 255 lph
Pump: GSS341-255
Volts: 13.5
Test Fluid S/G: 0.76
Fluid Temp: 69

PSIG Amps Lbs/Hr Gal/Hr Ltr/Hr Ltr/Min CC/Min Gr/Min Gr/Sec Gr/Sec
35 5.7 448 74.67 282.65 4.71 4710.84 3386.91 56.45 814.5
40 5.9 431 71.83 271.93 4.53 4532.08 3258.39 54.31 783.6
45 6.2 418 69.67 263.72 4.40 4395.39 3160.11 52.67 760.0
50 6.4 404 67.33 254.89 4.25 4248.17 3054.27 50.90 734.5
55 6.7 394 65.67 248.58 4.14 4143.02 2978.67 49.64 716.4
60 7.1 383 63.83 241.64 4.03 4027.35 2895.50 48.26 696.4
65 7.4 371 61.83 234.07 3.90 3901.17 2804.78 46.75 674.5
70 7.7 358 59.67 225.87 3.76 3764.47 2706.50 45.11 650.9
75 8 346 57.67 218.30 3.64 3638.29 2615.78 43.60 629.1
80 8.4 331 55.17 208.83 3.48 3480.56 2502.38 41.71 601.8
85 8.8 319 53.17 201.26 3.35 3354.37 2411.66 40.19 580.0
90 9.3 283 47.17 178.55 2.98 2975.82 2139.50 35.66 514.5
95 9.7 258 43.00 162.78 2.71 2712.94 1950.50 32.51 469.1
100 10.2 232 38.67 146.37 2.44 2439.54 1753.93 29.23 421.8

Note:
Bypass valve opens @ 95 psi
Horsepower value @ BSFC of 0.55

Make: Fake Walbro 255 lph
Pump: GSS341-255
Volts: 13.5
Test Fluid S/G: 0.76
Fluid Temp: 69

PSIG Amps Lbs/Hr Gal/Hr Ltr/Hr Ltr/Min CC/Min Gr/Min Gr/Sec Gr/Sec
35 12.3 419 69.83 264.35 4.41 4405.90 3167.67 52.79 761.8
40 12.6 410 68.33 258.68 4.31 4311.26 3099.63 51.66 745.5
45 12.9 400 66.67 252.37 4.21 4206.11 3024.03 50.40 727.3
50 13.2 389 64.83 245.43 4.09 4090.44 2940.86 49.01 707.3
55 13.5 378 63.00 238.49 3.97 3974.78 2857.70 47.63 687.3
60 13.7 367 61.17 231.55 3.86 3859.11 2774.54 46.24 667.3
65 14 360 60.00 227.13 3.79 3785.50 2721.62 45.36 654.5
70 142 350 58.33 220.82 3.68 3680.35 2646.02 44.10 636.4
75 14.6 341 56.83 215.14 3.59 3585.71 2577.98 42.97 620.0
80 14.9 334 55.67 210.73 3.51 3512.10 2525.06 42.08 607.3
85 15.2 321 53.50 202.52 3.38 3375.40 2426.78 40.45 583.6
90 15.5 311 51.83 196.22 3.27 3270.25 2351.18 39.19 565.5
95 15.8 300 50.00 189.28 3.15 3154.58 2268.02 37.80 545.5
100 16.1 291 48.50 183.60 3.06 3059.95 2199.98 36.67 529.1

Note:
Bypass valve opens @ XX psi
Horsepower value @ BSFC of 0.55

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