“Which size fuel pumpdo I need?”
According to the Summit Racing technical department, it’s one of the most common questions they hear. It’s not about the physical size of fuel pump; rather, the question refers to the volume of fuel the pump can flow.
Then you can refer to part 2 of my post, that the other fault in the alternator was causing a weak spark. Either way, a knackered alternator can affect mpg. His car has probably benefitted from having the battery disconnect as part of the alternator renewal as well though, it will have reset the ECU. Engine Performance Parameters Specific fuel consumption Low values of sfc are desirable, for SI-engines 250 – 270 g/kW.h and for CI-engines, 200 g/kW.h P m fc f & s = Engine Performance Parameters Gasoline engine.
Many companies rate fuel pump size based on gallons-per-hour (GPH), liters-per-hour (LPH), or lbs./hr. of free flow. Companies like Aeromotive also simplify things a bit by including a real-world horsepower rating with their fuel pumps.
We reached out to the fuel system experts at Aeromotive and Summit Racing to determine what you need to know when choosing a high performance electric fuel pump for your application. They’ve identified three key factors you need to know when selecting a fuel pump.
How Much Fuel Do You Need?
We’re talking fuel volume here. And there are really two things that come into play when determining fuel volume: vehicle horsepower and BSFC (brake specific fuel consumption).
In order to make the proper calculation, you need to start by determining your vehicle’s maximum horsepower. You can determine this by having your vehicle dyno tested or by making a reasonable horsepower estimate based on the manufacturer’s advertised horsepower plus an estimate of power gains made by aftermarket modifications. If you are making an estimate of your horsepower, Aeromotive suggests that you err on the high side to be safe.
BSFC (brake specific fuel consumption) is a measurement of the amount of fuel consumed per unit of power produced. According to Aeromotive, a typical gasoline engine will use less than one pound of fuel to make one horsepower for one hour, so you should expect the BSFC number to be less than one. However, this number will vary for every application, depending on the specific engine combination, power adders, fuel type, octane ratings, and more.
For example, Aeromotiveoffers these guidelines for BSFC:
Gasoline: Baseline
- Naturally aspirated engines: 0.4 to 0.5 BSFC
- Nitrous combinations: 0.5 to 0.6 BSFC
- Forced induction engines: 0.6 to 0.75 BSFC
Ethanol: Plan for 30-35% more fuel consumption than gasoline burning engines.
- Naturally aspirated engines: 0.6 to 0.7 BSFC
- Nitrous combinations: 0.75 to 0.8 BSFC
- Forced induction engines: 0.85 to 0.95 BSFC
Methanol: Plan for 100-200% more fuel consumption than gasoline burning engines.
- Naturally aspirated engines: 0.9 to 1.1 BSFC
- Nitrous combinations: 1.2 to 1.3 BSFC
- Forced induction: 1.8 to 2.0 BFSC
Again, these are just general guidelines. The recommended method for establishing BSFC is through proper flywheel dyno testing. In contrast to your estimated horsepower rating, you should lean toward the low side on your BSFC if you are estimating.
Once you’ve determined your engine’s horsepower output and BSFC, you can determine your vehicle’s fuel requirements using the following equations:
Optimal lbs./hr = (Max. HP x BSFC)
Optimal GPH = (Max. HP x BSFC) / 6
Optimal LPH = (Max. HP x BSFC) / 1.585
Using 650 horsepower, let’s figure out the fuel requirement (volume) for a naturally aspirated gasoline engine:
Optimal lbs./hr: (650 HP x .4 BSFC) = 260 lbs./hr. of gasoline
Optimal GPH: (650 HP x .4 BSFC) / 6 = 43.3 GPH of gasoline
Optimal LPH: (Max. HP x BSFC) / 1.585 = 164 LPH of gasoline
Based on volume, this answers the original question: “What size fuel pump do I need?” According to Aeromotive, though, this is just the first step in selecting a fuel pump.
Base Fuel Pressure
Keep in mind, a certain amount of fuel pressure is always required to maintain engine performance by assuring that fuel is available on demand. For example, most naturally aspirated carbureted street engines generally require between 6 and 8 psi. Racing applications and EFI setups will require more base fuel pressure. The key is to establish what that base fuel pressure will be and if, as with forced induction or certain “dry nitrous” kits, pressure will be required to change with engine load.
How does changing fuel pressure affect pump delivery?
As fuel pressure increases, the volume will decrease with everything else being equal. So as engine demand goes up, as is often the case in forced induction applications, the amount of required fuel pressure will increase, causing the fuel volume to the engine to go down. Other factors and conditions, such as acceleration G-forces and friction within the fuel system itself, will also affect fuel pressure.
To illustrate this, we’ve taken one of the most popular and efficient EFI pumps on the market: the Aeromotive A-1000 fuel pump (part #11101). Let’s examine five different scenarios to demonstrate the effect various fuel pressures have on flow volume:
- Carbureted, Naturally Aspirated, 9psi base pressure and 13.5v,
HP capacity 1,862 FWHP @ .5 BSFC = 931 lbs./hr. volume
- EFI, Naturally Aspirated, 43psi base pressure and 13.5v,
HP capacity 1,588 FWHP @ .5 BSFC= 794 lbs/hr. volume
- EFI Blown with 20psi boost, 1:1 Regulator, 43psi base pressure,63psi plus boost, and 13.5v,
HP Capacity 1,098 FWHP @ .65 BSFC = 714 lbs/hr. volume
- EFI Blown with 10psi boost, 4:1 FMU, 43psi base pressure, 83psi plus boost and 13.5v,
HP Capacity 975 FWHP @ .65 BSFC = 634 lbs/hr. volume
- EFI Blown with 6psi boost, 8:1 FMU, 43psi base pressure, 91psi plus boost and 13.5v,
HP Capacity 926 FWHP @ .65 BSFC = 602 lbs/hr. volume
Aeromotive A-1000 fuel pump.
With fuel pressures varying from 9 psi to 91 psi, flow volume is reduced a total of 35 percent. Comparing volume at 63 psi for a high boost kit with correct injectors to 91 psi for a low boost application, with small injectors and an FMU, volume is reduced by 16 percent.
Clearly rising fuel pressure has a notable impact on flow volume. What is not shown (and rarely published) is the devastating impact this has on less efficient, traditional pumping mechanisms used by much of the competition. It is obvious that eliminating unnecessary fuel pressure rise, e.g. removing an FMU and installing the correct injector, increases flow, maximizing the horsepower potential of any fuel system.
Voltage Supply
Often overlooked, voltage supply (as measured at the fuel pump terminals) is crucial to electric fuel pump performance. Voltage to an electric motor is like fuel pressure to an injector—more pressure in equals more volume out. Higher voltage at the pump terminals increases motor torque, resulting in more rpm and an increased flow volume for a given pressure.
Let’s go back and take a look at thatAeromotive A-1000 fuel pump. At 80 psi, this pump will see a 22 percent increase in volume when voltage is increased from 12 volts to 13.5 volts. This can make or break pump performance, especially at high pressures. The key here is to figure flow at voltage based on whether an alternator is used or not. Often deleted on drag cars, the lack of a correctly sized and properly functioning alternator is vital to consider when choosing a fuel pump.
Armed with this knowledge, you’ll be able to make an educated decision on which performance fuel pump is right for your vehicle.
If you're concerned about the price of gas or want to minimize the impact of your driving on the environment, you don't have to scrap your car for a hybrid or a subcompact econo-box.
Did you know that a vehicle can burn up to 30 per cent more fuel if proper maintenance is not performed on a regular schedule? We all know the importance of regular car maintenance, but for many reasons, we just don't do it often enough.
I am asked more questions about fuel economy than any other topic. Short of becoming a 'hyper-miler,' these tips will help you use every last drop of fuel you pour into your tank.
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1. Check your tire pressure at least once a month. Under-inflated tires burn more fuel. If tires are 8 pounds under inflated, (not an uncommon condition), rolling resistance of the tires increases by 5 per cent.
2. At the pump, keep the hose in the tank until after the pump shuts off and make sure you allow all the fuel to pour out of the nozzle. As much as a quarter of a cup can pour from the hose. It's yours, you paid for it.
3. When appropriate, use your cruise control. This can save you up to 6 per cent in fuel consumption on the highway.
4. Corroded battery cables cause the alternator to work harder, using more gas. Have them cleaned as a matter of course with each engine check-up.
5. Don't let the vehicle idle for more than a minute. Idling consumes half-a-gallon to one gallon of gas per hour and pumps needless CO2 into the atmosphere. The modern engine will consume less fuel turning off and re-starting than idling for extended periods. We are already being faced with no-idle zones. Also, to effectively warm an engine, drive it, don't rev it. Engines only work hard under load and will warm up much quicker if you simply start the engine, wait for 20 seconds, (this builds the oil pressure,) and drive away.
6. Change the air filter at least the set number of times outlined in the owners manual, more if you drive in dusty conditions.
7. Have a regular engine check-up. Since the advent of computer controlled fuel injection, there is no such thing as an old fashioned 'tune-up' any more. At worst, you may be expected to replace spark plugs, oxygen sensor, the air and fuel filters.
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8. If your car was built since the mid-1980s, chances are it has an oxygen sensor in its exhaust system. It should be replaced just as you would spark plugs, following the manufacturer's recommendations. This little device trims the fuel delivery and has a profound effect on fuel economy in the process.
9. Driving in the highest gear possible without labouring the engine is a fuel-efficient way of driving. Driving at 60 km/h, a vehicle will use 25 per cent more fuel in third gear than it would in fifth. Travelling at fast rates in low gears can consume up to 45 per cent more fuel than is needed. If you have an onboard trip computer, you probably have an 'Instant fuel economy' setting. Watch this gauge and keep the litres per 100 kilometres as low as you can. The manufacturers have turned this into a bit of a game. The new Ford Fusion Hybrid has a leafy graphic display that sprouts leafs each time you reach a fuel economy milestone. I had the opportunity to drive one and each time we pulled into the driveway, my son would ask 'How many leaves on the tree, Dad'?
10. Think ahead! Drive smoothly. By applying light throttle and avoiding heavy braking, you can reduce both fuel consumption and wear and tear. Research suggests driving techniques can influence fuel efficiency by as much as 30 per cent.
11. Lighten your load. Think carefully about what you need on a journey. If you do not need something, do not pack it. Remove roof racks if not needed, as they create wind drag. The lighter the load, the lower the fuel consumption and emissions. An extra 100 pounds in the trunk reduces a typical car's fuel economy by 1 to 2 per cent. Carrying excess weight wastes gas.
12. Choose the right octane gas for your car. Check the owner's manual to find out what octane your engine needs. Octane ratings measure gasoline's ability to resist engine knock. But the higher the octane, the higher the price. Only about 6 per cent of cars sold need premium gas. Still, premium gas accounts for about 10 per cent of all gas sold. Resist the urge to buy higher octane gas for 'premium' performance.
13. Combining errands into one trip saves you time and money. Several short trips taken from a cold start can use twice as much fuel as a longer multipurpose trip covering the same distance when the engine is warm. Trip planning ensures that travelling is done when the engine is warmed-up and efficient.
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14. You can improve your gas mileage by one to two per cent by using the manufacturer's recommended grade of motor oil. For example, using 10W-30 motor oil in an engine designed to use 5W-30 can lower your gas mileage by one to two per cent. Thicker oil is harder to pump. This adds to parasitic horsepower loses.
15. Avoid 'revving' the engine, especially just before you switch the engine off; this wastes fuel needlessly and washes oil down from inside the cylinder walls. This is really bad thing for the next start up, as the cylinder walls will be dry.
16. Drive steadily. Slowing down or speeding up wastes fuel. Also avoid tailgating. Not only is it unsafe, but if affects your economy if the other driver slows down unexpectedly.
17. Do not rest your left foot on the brake pedal while driving. The slightest pressure puts 'mechanical drag' on components, wearing them down prematurely. This 'dragging' also demands additional fuel usage to overcome the drag.
18. Avoid rough roads whenever possible, because dirt or gravel can rob you of up to 30 per cent of your gas mileage. Every time the wheels bounce up and down, forward motion energy is removed from the vehicle. The best way I can describe this is to experience driving on a 'washboard' road. Not only is it very uncomfortable, the vehicle will actually slow down from the transfer of energy - and you thought physics classes would have no application later in life! This causes the driver to apply more throttle - wasted fuel.
19. Inspect suspension and chassis parts for misalignment. Bent wheels, axles, worn shocks, and broken springs can contribute to drivetrain drag, not to mention the unsafe condition they create.
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20. SUV owners should consider switching from an aggressive patterned off-road tread to a fuel efficient highway tread.
These are some of my observations and some of my responses to many questions about fuel economy. I'm sure you have your own and I would invite everyone that reads this to add their experiences on the comments tab of this story. And yes, this includes you hyper-milers out there.
Will we ever share Europeans' taste for premium-priced small cars? Fuel prices will be the determining factor. If they remain at current levels or even drop, then the push to small vehicles with European roots might be a flop