The “golden ratio” of combustion is the precise balance of air and fuel. As performance modifications increase the amount of air an engine can ingest, the fuel system must be upgraded to match. Without adequate fuel delivery, even the most sophisticated forced induction system will fail to deliver its potential. In this guide, we’ll explore modern fuel system components and how to properly size them for performance applications.

The Fuel Pump: The Heart of the System

The fuel pump is responsible for moving fuel from the tank to the engine at the required pressure and flow rate. Without sufficient flow, the engine will suffer from fuel starvation, especially under high-demand conditions.

Function

Fuel pumps must overcome several challenges:

• Moving fuel through filters, lines, and rails to the injectors
• Maintaining consistent pressure despite varying engine demands
• Providing adequate flow at all engine speeds and loads
• Operating reliably in a wide range of temperatures

Metrics

The key performance metric for fuel pumps is Liters Per Hour (LPH). This measures the volume of fuel the pump can move in one hour under specific conditions. Stock pumps are sized for the vehicle’s original power output, and adding forced induction or other modifications can quickly overwhelm them.

For example, a stock fuel pump in a typical 200hp vehicle might flow 120-150 LPH, but a modified engine making 400hp may require 255 LPH or more. It’s critical to calculate your fuel needs before making modifications.

Upgrades

Popular upgrade options include:

• Walbro 255 LPH: A popular “go-to” upgrade that can support approximately 400-500hp depending on the application.
• AEM 340 LPH: A higher-flowing option for more substantial power increases.
• Carter Competition Pumps: High-flow options for extreme applications.

It’s important to note that upgrading the fuel pump often requires supporting modifications:

• Wiring Upgrades: Higher-flow pumps draw more current and may require upgraded wiring to prevent voltage drop.
• Relay Upgrades: Stock relays may not be able to handle the increased current draw.
• Fuel Lines: Larger diameter lines may be needed to support increased flow.

Fuel Injectors: The Gatekeepers

Fuel injectors are the final component in the fuel delivery chain, responsible for atomizing fuel and metering the precise amount needed for combustion.

Function & Sizing

Injectors atomize fuel by forcing it through a small orifice at high pressure, creating a fine mist that can burn efficiently. The size of an injector is measured in cubic centimeters per minute (cc/min) or pounds per hour (lb/hr).

To calculate the required injector size, you can use the following formula:

Required injector size = (Max HP × BSFC) / (Number of cylinders × Max duty cycle)

Where:

• BSFC (Brake Specific Fuel Consumption) is typically 0.5 for naturally aspirated engines and 0.6 for forced induction
• Max duty cycle should be limited to 85% for safety

For example, a 400hp turbocharged engine with 6 cylinders would require injectors sized at:

(400 × 0.6) / (6 × 0.85) = 47 cc/min per injector

Injector Duty Cycle

Injector duty cycle is the percentage of time an injector is open during each engine cycle. It’s a critical tuning parameter:

• 100% duty cycle means the injector is constantly open
• 0% duty cycle means the injector is never open
• Aim to stay below 85% duty cycle for safety and longevity

Running injectors at or near 100% duty cycle can cause several problems:

• Overheating of injector components
• Poor atomization at extreme duty cycles
• Inability to increase fuel delivery if needed

Technology

Fuel injector technology has evolved significantly over the years:

• Saturated Injectors: Older technology where the same voltage is applied throughout the injection pulse. Simple but less precise.
• Peak & Hold Injectors: Use a high initial voltage to open the injector quickly, then reduce voltage to hold it open. More precise and responsive.
• EV6-Style Injectors: Modern high-impedance injectors with even more precise control and faster response times.

Supporting Cast

A properly functioning fuel system requires attention to all components:

• Fuel Pressure Regulator: Maintains consistent fuel pressure relative to manifold pressure. In return-style systems, it returns excess fuel to the tank.
• Fuel Rails: Distribute fuel to each injector. Upgraded rails may be needed for high-horsepower applications to prevent fuel starvation.
• Fuel Filters: High-flow applications may require larger or additional filtration to protect expensive components.

Conclusion

The fuel system is often overlooked until it becomes a limiting factor. Properly sizing and upgrading fuel components ensures that all the air being forced into the engine can be properly matched with fuel. Whether you’re adding a turbocharger, supercharger, or simply extracting more power from a naturally aspirated engine, adequate fuel delivery is crucial for both performance and reliability.