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Designing the Optimum Fuel System

The first and most important term to focus upon comes from the title of this article. That word is “System”. The fuel system is just that, by definition—a system. Understanding what defines a system and the planning involved for a specific vehicle is the first priority.

-noun: “an assemblage or combination of things or parts forming a complex or unitary whole”
When planning a vehicle’s fuel system, first consider a short list of important factors before opening the wallet and randomly purchasing parts based upon advertising, friend recommendations, or some online article—including this one! Choosing the correct combination of fuel system components is imperative to optimum output, consistency, and reliability. Quality fuel system components are not inexpensive, and installing the wrong parts make the costs that much higher in the long run. Mistakes in component selection can cause component failure, power loss, inconsistencies at the race track, or permanent engine damage. Here are are few questions to consider;
  • How large is the engine?
  • How much horsepower does the engine produce?
  • Is this a street, street/strip, off-road, marine, RV/Towing, or race-only application?
  • Is the engine fuel injected or carbureted?
  • What fuel pressure is required (this is determined by many factors)?
  • Is the engine supercharged, turbocharged, or using nitrous?
  • Does the application use  gasoline or alcohol for fuel?
  • If class racing, what do the rules allow regarding component selection?
  • Is the available budget adequate to create the proper fuel system for the application?

Fuel Demand

When calculating fuel demand, engine size, horsepower, application and intended use, fuel type, and whether the engine is fuel injected or carbureted are the initial considerations. It is impractical to add a fuel pump that is too large for an low power engine, and detrimental to the opposite, when a fuel system that is too small or does not meet demand. Please read our Fuelish Tendencies article to help determine fuel pump size for a gasoline engine.
Fuel supply is based upon two parameters: pressure and volume. The volume of fuel must be matched to the requirements of the engine throughout the RPM range. A pump that is too small will starve the engine for fuel. The delivery pressure must meet component requirements to maintain correct air/fuel ratio, fuel atomization, and instant fuel availability (carburetor float bowls or fuel injector requirements).
On forced induction (supercharged or turbocharged) or nitrous applications, it is imperative to plan for the additional fuel demand these components require when experiencing boost or engaging the nitrous system. One segment of engine survival is directly related to proper fuel delivery. When an engine enters or builds upon a boosted state, or the nitrous system is activated, the capability of the fuel system is put to the test. It must instantly meet and maintain the additional fuel demand—efficiently, and repeatedly without fail. On applications that utilize nitrous oxide, it is best to have two independent fuel systems. One for the engine, and one specifically for the nitrous system.


Just because someone installed a clear, viewable $5.00 inline filter before the carburetor does NOT confirm the fuel system is adequately filtered! Common commercial underground fuel tanks hold plenty of dirt and particulates that we never see, and this contamination easily transfers to or exists inside of the vehicle’s fuel tank, so why take a chance with a basic filter? Proper filtering should begin before the fuel pump(s) on the vehicle and also before the final destination (carburetor or fuel injectors). The bare minimum includes a high quality canister-style or inline filter on each line before the fuel pump, then a cleanable screen inline filter before the carburetor, injectors, or nitrous system fuel solenoids. Any small particle contaminant that enters the fuel system could easily interfere with fuel flow or damage the fuel pump, regulator, or other components—and that does not include possible engine damage as a result. Here is a true story of one such catastrophe:

Many years ago an acquaintance installed a plate nitrous system on a pristine, original 1968 Camaro RS. He and another friend hastily installed the kit one afternoon so they could show it off at a cruising event and possible street racing later that evening. The install was quick and sloppy. A few days later, after repeatedly activating the nitrous during a few more test runs on a road outside of town, he parked the car at a friend’s home for a visit. It sat there for a few hours and later that evening when he returned to his vehicle—not realizing or really caring that he had left the nitrous bottle valve open—he went to start the car and go home.

To be clear, leaving the bottle valve open is not too serious of a problem—if a system was installed correctly. However, the fact that they did not install a filter (screen fitting) in the nitrous feed line before the nitrous solenoids was a problem. Days later, the excuse was that the person helping, A) did not feel it was necessary, and B) what they had was not the proper size. Debris accumulated in the nitrous feed line during installation and entered the nitrous solenoid enough to prevent the solenoid from fully closing.

Over the time he was visiting the other friend, the nearly full nitrous bottle slowly emptied into the engine. Although nitrous does not ignite by itself, when attempting to start a now-stubborn engine, the pin (using a grenade analogy) had been pulled. Thinking it was starving for fuel he pumped the throttle a few times before experiencing the best ignition of his life. When the engine fired, the residual nitrous and cold-start fuel ignited, or better stated—exploded. The short list of damages included:

– (2) broken pistons
– (1) bent connecting rod that partially exited the cylinder wall
– (1) pushrod through a valve cover (this was one of the most interesting to see)
– Various broken rocker arms
– A few bent valves
– Camshaft broken in two
– (2) destroyed (shattered) spark plugs
– The nitrous plate was broken in half
– Carburetor base plate cracked and throttle blades bent upward around the cross shaft
– One mounting boss on the intake for the carburetor broken off
– One muffler launched right off the exhaust piping
– Various broken bolts
– And, a dented hood and inner fender on an otherwise pristine Camaro RS

I was working at a local automotive machine shop at the time and although I had heard about this event immediately, it took him a few days before he brought in the boxes and buckets of various parts from what was left of his engine to see if we could salvage anything. All that damage because he and a friend were not cautious and responsible during installation. Ignoring or taking shortcuts related to necessary safety precautions can get expensive quite quickly. A simple filter screen on the nitrous line could have saved that engine and a costly hit to his wallet.
It is important to note this result was unique. An abundance of nitrous entered the engine and the explosion occurred while cranking a cold engine. It was initially difficult to fathom so much damage could occur.

Proper filtering of the fuel itself is just as important. If an engine goes lean (lack of adequate fuel pressure or volume), engine damage can and will occur. The more powerful or modified the engine, the more important this becomes, and greater the chance of catastrophic failure.

Intended Use of Vehicle

Different uses require slight changes to the fuel system design. On a drag race application, design a system that is optimized for drag racing. The same holds true for circle track or road racing, street, or off-road. Drag race applications operate for seconds at a time and must fend off the g-forces created during acceleration. Circle track applications must operate at full fuel delivery for hours at a time (different angle of g-force). Off-road applications are subject to extreme shock abuse, and street applications have to function efficiently over a wider operating range, dealing with heat, emissions, and other concerns. All system variations demand high attention to safety and reliability.
For most circle track applications the rules mandate mechanical style pumps. For these applications a belt-driven pump is more efficient because of the run time. Drag racing applications must fight g-forces at launch and save as much weight as possible. Plus, a drag race engine is not operating at near steady-state RPM as a circle track car. The acceleration of a drag car mandates larger output pumps, and higher instant demand. Off-road applications need to survive jumps and odd travel angles from the terrain, causing various delivery concerns. Street applications are abused by heat, road debris, the dirtiest fuel, and have to be relatively economical, emission-compliant, and operate through a wide RPM range.

Fuel Pressure Regulation

Proper fuel pressure is important for a variety of reasons. We detail the differences between dead head (blocking) style versus return (bypass) style regulators in our Fuelish Tendencies article. Maintaining correct fuel pressure is important to the consistent and efficient operation of every engine. Too little or too much fuel pressure can cause air/fuel mixture problems, component damage from lean conditions, lost power, lowered efficiency, higher emissions, and shorter engine life. Example:

POOR System — (one large system with two regulators in series “not recommended” … and no filters after regulators)

Poor design fuel system

Good Street and Street/Strip System … Return regulator system on carbureted applications. Note however that it is missing a filter after the regulator. Oops!


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Please review other Fuel System related tech articles