In the quest for more horsepower, we add bigger cams, bigger intakes, and bigger pistons. Why is it then that we don't make provisions for the larger demands placed on the fuel system? We've seen guys have 8-71 blowers atop their RB engine, only to see a 5/16-inch fuel line with one of those glass surrounded screen fuel filters before the carb. Sure, most of us will never need a 3/4-inch fuel line with a 500-gph fuel pump, but the fuel system must be considered when upgrading your drivetrain. Heck, even if not increasing the cubic-inch displacement, the fuel system should at least be checked out to make sure it's functioning properly.
There are different kinds of fuel systems, and the one you use is directly proportionate to the engine's requirements. Whether you use a "dead head" system that consists of a fuel line with a filter and fuel pump ending at the carburetor or a return-style system that circulates the fuel from the tank to the carb with a bypass for excess fuel to go back to the tank, making sure all the components are working correctly is, or at least should be, a major concern. Pressures and volumes vary depending upon the kind of fuel used (gasoline or alcohol), and the type of fuel system employed. with routine maintenance, a good fuel system will pay dividends; yet many cars are fitted with fuel systems that fall below the necessary standards. With a little help from Barry Grant/Demon Fuel Systems of Dahlonega, Georgia, we have compiled a short list of the most common mistakes in fuel systems, and a guide to correct them.
Squeezing The Juice
One of the biggest mistakes made when designing a fuel system is choosing the incorrect line size. While a 5/16- or 3/8-inch line may be appropriate for a stock or mildly modified street vehicle, it is not suggested for an application designed on a racing fuel system between the fuel cell and the pump. Racers often joke about their first race car, and how the fuel line was so small it functioned as the main jet. Ensure the fuel is supplied through lines that are the correct size for the application. Push-Lok, stainless steel braided hoses, and aluminum tubing are the most common fuel lines used on race cars.
Right-Angle Hose-End Fittings From The Pump To Carburetor
Cars like the famed Six-Pack-equipped Road Runner used brass fittings to plumb the induction. Unless doing a restoration of one of these styles of cars, avoid forged 90-degree elbow fuel fittings as much as possible. Although they are inexpensive and readily available, they're restrictive and frequently cause fuel flow troubles. Hose ends with angles of 90 and 45 degrees should also be avoided, if possible. should it become necessary to use one, use radiused-style hose ends (90-degree bends) as they have much better rates of flow. They're manufactured from aluminum, equipped with swivel ends for a positive seal, and are easy to install.
Yep, It Fits
All too often, we see cars with too large a carburetor. we have even seen basically stock 318s with tunnel rams. Carburetors are designated by their venturii size. Having the proper venturii size for a given application ensures the carburetor generates sufficient air speed. Air speed creates the necessary depression (low pressure) to draw fuel through the metering systems and booster venturii into the air stream to be atomized. The Race Demon, which is equipped with removable venturii sleeves, boosters, and so on, overcomes most of the sizing problems. When choosing the right carburetor, engine size, camshaft characteristics, and heads play a critical role.
This comparison shot of these...
This comparison shot of these two fuel lines is of a stock 5/16-inch steel line and an upgrade to 3/8-inch going into a mildly modified street car.
The fuel filter is one area...
The fuel filter is one area that should not be overlooked. The absence of a fuel filter will cause more headaches than the supposed increase in flow by their absence. But what kind of filter is right for your application? Fuel filters come in two different configurations: paper and metal. A paper filter is a good option when dealing with standard automotive fuels. If you add alcohol or other fuels, a steel filter will be required. Not only is having a fuel filter a good idea, but maintenance of your filter is a must. Unless you want to experience problems with the way your engine runs, it will need to be changed from time to time. To protect the fuel pump and carburetor, use a good filter before the pump and filtered fittings at the carburetor.
The BG-5000 fuel filter features...
The BG-5000 fuel filter features billet aluminum construction and is compatible with both gasoline and alcohol.
The Race Demon with ConcentraCast...
The Race Demon with ConcentraCast venturii, removable boosters, billet metering-blocks, large capacity fuel chambers, and billet aluminum baseplate strives to achieve higher levels of consistent performance than conventional designs. Concentracast is a new die-casting technology employed by Demon Carburetion. It is the most repeatable method of producing concentric venturii without misalignment or core shift.
This inline fuel filter is...
This inline fuel filter is made of billet aluminum construction with a stainless steel element for use with gasoline or alcohol. A paper element is available for gasoline use only.
This six-valve mechanical...
This six-valve mechanical pump is available in two versions: 9-psi for gasoline or 15-psi for alcohol. With a capacity to deliver up to 130 gallons-per-hour, the six-valve pump requires a diaphragm bypass when used with gasoline and a throttle bypass for alcohol.
In a hypothetical case, let's say we have a 360 LA engine with 11.0:1 compression and a camshaft with .258-degrees of duration at .050-inch lift. Right off the bat, according to the carb selection charge at www.barrygrant.com, we can see a Road Demon 725-cfm vacuum secondary carb would be too small. On the other hand, a Mighty Demon 750-cfm mechanical carb would be ideal. Always get the manufacturer's suggestion when choosing a carb.
Finally, no fuel system is complete without placing some thought into the air that enters the carb. A quality air filter is a must, and advancements in filtration technology have made the air filter welcome on any performance engine due to its increased air-flow. Tests have proven that the right air filter shows negligible decreases in horsepower on the dyno.
Whether to use a mechanical or electric fuel pump depends on personal preference, and the demands that will be placed on the fuel pump. In the past, the prevailing thought was that you must use an electric pump for performance applications. Depending on how much performance you are looking for, that is true. But with the advancements made in fuel pump technology, a mechanical is now a viable option when a certain amount of performance is desired. Another consideration when using a high-volume pump is a regulator. If a fuel pump delivers more than 7 1/2 psi, it will overpower the needle and seat, and flood the carb. A regulator is an adjustable device that plumbs in the fuel system after the pump, and regulates the fuel pressure to the carb. Again, consult the manufacturer for their recommendations. If you do use an electric fuel pump, be sure to use a relay in the electrical system to ensure the pump is provided with the proper voltage in order to maintain proper fuel flow.
This Rush Air filter uses...
This Rush Air filter uses premium U.S. long staple cotton in a stable sandwich of aluminum mesh. Long staple cotton has much longer "whisker" fibers extending into the airflow than other competitive materials. As air moves through the filter that is treated with the specialty filtration oil, the longer whisker is more active as it waves back and forth, sweeping the air, seeking out and capturing the passing dirt particles as they pass through the filter. The longer, more active, oil-treated "whiskers" provide greater filtration surface to attract and retain engine-damaging dirt, while optimizing airflow over conventional paper filters.
When it comes to getting the...
When it comes to getting the fuel to the carb, having more than 6 1/2 to 7 p.s.i. will definitely cause headaches. The excess pressure will force the fuel past the needle and seat, and flood the engine. Definitely not something you want to deal with. These fuel logs will connect the carb to the fuel source, and they can be ordered with an internal regulator.