The best engine in the world is nothing more than an expensive boat anchor if it cannot get the proper amount of fuel. An engine that could twist the dyno out of the floor is crippled if fuel delivery is compromised. The best carburetor in the world is useless if it is choked by inadequate fuel delivery. If the fuel delivery system is critical, where do you start to ensure you have the right components and the proper layout?
The decision to race with gasoline or alcohol will be a significant determining factor in selecting the pump, filter and fuel line. If alcohol is the fuel of choice, remember it requires roughly twice the volume of alcohol to equal gasoline, so all aspects of the fuel delivery system should be capable of delivering this increased volume.
But once you make your decision on fuel, the task of choosing the right components and installing them correctly is your challenge. There are several options available to racers, according to the folks at Barry Grant Inc., manufacturers of BG Fuel System products and Demon Carburetors.
Plumb It Right ... The First Time!
One of the first things that should be done is to make sure the fuel cell bladder and the foam within are in good shape. Over time, the fuel can cause the quality of the foam to decrease, which causes many problems in terms of clogged fuel filters.
Sizing the fuel line from the tank to the pump is very important. Lose volume here and everything else is a waste of time. Technicians at Barry Grant, Inc. recommend plumbing a car less than 500 hp with -8 AN line between the pump and the carburetor. Late Models and other high-horsepower applications (more than 500hp) should use a -10 AN line from the fuel cell to the pump and an -8 AN line from the pump to the carburetor.
On an alcohol car, the need for increased fuel delivery means you’ll need a larger fuel line. Use a -10 AN line between the fuel cell and the pump, -8 AN line from the pump to the carburetor and a -8 AN line from the bypass to the fuel cell, unless the component manufacturer recommends otherwise. Always use radiused fittings (hose ends) with the least amount of radius needed to do the job. Think of the plumbing as air moving between the carburetor and the intake valve. You wouldn’t have a sharp turn in the intake runner, so why would you do it with fuel-line plumbing?
Push-Lok and braided stainless steel hoses are the two most prevalent types of fuel lines currently in service. The quick assembly feature of the Push-Lok hose fittings makes this style of plumbing popular with circle-track racers. The hose-end fittings are available with swivel ends, which are easy to install and the finished hoses are less expensive than the braided stainless steel variety. Push-Lok lines are constructed with a braided nylon inner carcass and a protective rubber outer shell.
However, the braided stainless steel line is a standard of the industry, with higher abrasion resistance. The lines and the aluminum AN fittings are readily available and have higher burst and operating pressure ratings. Properly installed braided stainless steel lines will not leak, resist collapsing or kinking, do not cut easily and will accept much abuse. Check your rule book to see if there is a hose type specified before you order!
When you are routing lines, keep them as far from electrical wiring (including battery cables), as possible. Use high-quality plumbing brackets throughout the installation. Always plumb your car as the rules mandate. Never pass the fuel line through the cockpit area. If the fuel line needs to pass through a chassis bulkhead, always use bulkhead fittings of the correct size. Never cut a hole and pass the fuel line through the bulkhead.
Keep the fuel plumbing away from the driveshaft and the suspension. Pay attention to the suspension travel—the last thing you want is the fuel line being pinched when the rear axle housing or the control arms are in full compression. The same amount of common sense should be used when passing near the exhaust system—keep away from it! Keep the lines well above the lowest portion of the chassis framerails, and they should be mounted well inboard and never near the jack points or where jackstands might be used.
Plumbing Safety
“Break-away” shut-off valves are an important safety device that should be on any race car. In case of a crash in which the fuel line is ruptured, these valves are designed to close on the loss of pressure and completely seal both halves of the fuel supply automatically.
Fuel Filtration
Many racers feel if they put clean fuel into the fuel cell, there is no reason to filter the fuel after it leaves the tank. They are wrong. Over time, additives in racing fuel may break down the fuel cell foam material or the fuel line, putting small pieces of foam or rubber into the fuel. Always have a filter on the fuel cell breather to keep bits of rubber, dirt and other track debris out of the fuel system.
A fuel filter with a replaceable element can save pumps and loss of pressure. Paper filtration material is fine for gasoline, but for alcohol applications, a steel mesh filter is preferred because alcohol will cause the paper element to swell and choke off fuel.
Pumps
Mechanical and diaphragm fuel pumps are the standard of circle-track racing. Electrical fuel pumps are generally prohibited for safety reasons, although some fuel cells have submersible electric fuel pumps located in the cell itself (see separate story on ATL’s new cell for the ASA series in this issue).
There are three styles of mechanical pumps: the block-mounted, cam-driven diaphragm pump used for decades, the gear-style, belt-driven mechanical pump and its cousin, the hex-drive gear pump.
The diaphragm pump is one of the most reliable high-volume pumps available and can be used for either gas or alcohol. Over the years, improvements have been made in the design, and many pump manufacturers offer more than one pump. Barry Grant’s Super Speedway pump, for example, is a high-volume pump that requires neither a throttle bypass nor a pressure regulator. This gas-only pump features enlarged ports for increased fuel flow and maintains the 7.5- to 8-psi pressures most gasoline carburetors require. The company’s Six-Valve pump is available in two pressure ratings: the 7psi version is for gasoline, which doesn’t require a throttle bypass or pressure regulator, and the 15psi pump can be used with alcohol or gasoline. The 15psi pump requires a two-stage, diaphragm-type pressure regulator for gasoline or a throttle bypass to return excess fuel to the fuel cell for alcohol.
The gear-style pump has grown in popularity over the past few years as racers demand greater control over the consistency of pressure and delivery for high-rpm, high volume requirements. The belt-driven and hex-shaft style (driven off the camshaft, oil or power steering pump) use two meshing gears turning toward each other (called counter-rotating or opposing gear) to pull fuel from the cell then push it to the carburetor.
Because gear-style pumps are manufactured to very close tolerances, a fuel filter must be added into the fuel system before the fuel enters the pump. Additionally, these pumps are self-lubricating and must not be run dry, or the assembly will seize.
The belt-style pumps are popular in pavement racing where debris is not much of a problem. However, the belt-style pumps have fallen from favor in dirt-track racing series because dirt clods or rocks could easily break the belt. The hex-style pump (using the standard Hilborn/Enderle-style three-point bolt mount) has replaced the belt-driven pump on dirt.
The tech team at BG Fuel Systems offers some recommendations for pump selection. Gasoline engines up to 650hp can use diaphragm pumps successfully. At more than 650hp, a belt- or hex-drive pump and a two-stage diaphragm bypass are preferred. Alcohol engines up to 500hp can use the diaphragm pump in conjunction with a throttle bypass. Over that figure, go with a gear-style pump and a two-stage diaphragm bypass.
Fuel Bypass
Because gear-style pumps have the capacity to deliver tremendous amounts of fuel (65-400+ gallons per hour) at high pressures (13-100psi), they require a means of returning excess fuel back to the fuel cell. The recommendation is to use a two-stage, diaphragm-style bypass.
The diaphragm bypass (regulator) will allow the pressure to be pre-set with the spring-loaded diaphragm, with excess fuel returning to the tank when the pressure exceeds the preset. When using a gear-style pump on gas, Barry Grant technicians recommend a two-step diaphragm bypass with an idle jet (pill) to provide the progressive fuel curve needed to meet the needs of the engine. By changing the size of the pill, you can raise or lower the fuel pressure at idle—larger pill, lower idle pressure; smaller pill, higher idle pressure.
Another style of bypass, the “poppet,” is for gear-driven pumps and uses a spring-ball-style check valve to release the excess fuel with a pill controlling the fuel pressure. This style of return valve does not react to pressure changes as rapidly as a diaphragm style and, for that reason, is seldom recommended.
For an alcohol engine up to 500hp equipped with a diaphragm pump, a throttle bypass system mounted on a plate beneath the carburetor is the desired setup. Recommended pressure settings are 3-5psi at idle and 9-11psi at wide-open throttle. Once the linkage is properly adjusted, the slot in the shaft where the throttle position arm is attached is the key to pressure adjustment. The factory setting is at horizontal, and moving the slot clockwise will increase the fuel pressure. Moving counterclockwise will decrease it.
Pressure Gauges
When establishing a fuel system, fuel-pressure gauges are a very useful tool. Pressure gauges should be mounted to check the pressure from the pump and at the fuel inlet to the carburetor. Barry Grant recommends a dampened movement-style gauge, which is not impacted by temperature or by vibration. A 15psi gauge is recommended for measuring the pressure in the carburetor inlet and a 30psi gauge for measuring the output from the pump.
Grant’s tech staff says rough fuel pressure settings can be made in the pits at idle or at part throttle. However, the true measurement of how the system is functioning can be made only on the track when the car is under load at wide-open throttle. The gauges should be placed in the driver’s compartment with the “normal” reading at the 12 o’clock position.
The overall health of the fuel system is critical to engine performance. It’s not just bolting on the latest stuff, filling the car with fuel and going out to race. Failure to provide a well-designed and executed system—from the fuel cell to the carburetor—can ruin a whole weekend at the track, or, just maybe, a whole season.
