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HIGH FLOW Fuel Injectors
( fuel injector tech 101 )

When do you need larger injectors?

When you increase boost above 16 psi or above 500 HP we have found that the factory fuel injector become inadequate. The fuel injector flow must be matched to the airflow requirements of the engine over the entire rpm operating range. The injectors must be able to supply a large amount of fuel at wide-open throttle to prevent high rpm lean out, and transitional amounts to cover all of the operating conditions in between. Supercharged engines in particular place even more rigorous demands on an injectors range because of their increased airflow capability.

Choosing the Correct Fuel Injectors

Electronic fuel injectors have two masters to satisfy. They must accurately match the fuel demands of an engine while meeting the electronic commands of the engine management computer. Obtaining the correct fuel flow amount from a group of injectors in an EFI system is similar to determining the right size jets for a carbureted engine. The fuel flow of both systems must be matched to the airflow requirements of the engine over a broad rpm operating range. The injectors must be able to supply a small amount of fuel to support engine idle, a large amount at wide-open throttle to prevent high rpm lean out, and transitional amounts to cover all of the operating conditions in between. Turbo/superchrged engines in particular place even more rigorous demands on an injectors range because of their increased airflow capability. Just as the wrong-sized jets in a carb can cause driveablity problems such as rough idle, surging, poor throttle response or even high-rpm lean-out causing scattered engine parts, so can incorrectly sized injectors. The following is a guideline equation for approximating fuel flow per injector based on estimates on engine Horsepower (HP) and Brake Specific Fuel Consumption (BSFC). Engine HP must be a realistic estimate of engine output. BSFC is determined from engine dynamometer measurements. It typically ranges from 0.4-0.6 for gasoline powered engines. A BSFC of 0.55 is a reasonable initial estimate for a supercharged engines. The 0.8 multiplier of the "Number of Injectors" helps us derive a practical, maximum "Injector Flow Rate" for each injector based on an effective real world injector operating pulse time and fuel flow. It's unrealistic to establish the fuel flow to the engine based on an injector operating pulse time of 100% (wide open all the time). This formula uses an injector operating cycle based on 80%. Some full race engine management systems may operate at 85-95% duty cycle, but doing so for some time increases the likelihood of overheating the injectors which may cause irregular fuel rates or a decrease in low rpm operation. Injector Flow Rate (lb/hr) = Engine HP x BSFC Number of Injectors x 0.8 For example, to calculate the individual injector size for a 650 HP V8 using 8 injectors and a BSFC of 0.55 Injector Flow Rate (lb/hr) = 650 x 0.55 8 x 0.8 = 55.85 lb/hr Using the formula above injectors with a flow rating of 56 lb/hr static flow at 43.5 psi (3bar) fuel system pressure would be an adequate injector selection. If you have a known injector fuel flow rate you can solve the above equation for a rough estimate of fuel system capacity like this: For example, using the same estimated values from above: Engine HP = 50 x 8 x 0.8 0.5 = 640HP Injector Size HP MAX. Application Price 60/62-Lb (EV6) Forced-Induction HP 816 hp @ 85% Duty Cycle Naturally Aspirated HP 628 hp @ 85% Duty Cycle USCAR Design 60/62-Lb Fuel Injector (high impedance) USCAR Design Conncetor Injectors are Packaged in sets of (8) EV6 Connector type $ 410.00 42-Lb (EV1) Forced-Induction HP 751 hp @ 85% Duty Cycle Naturally Aspirated HP 439 hp @ 85% Duty Cycle Jetronic/Minitimer Design 42-Lb Fuel Injector (high impedance) JETRONIC/MINITIMER Design Conncetor Injectors are Packaged in sets of (8) EV1 Connector type $ 320.00 39-Lb (EV6) Forced-Induction HP 530 hp @ 85% Duty Cycle Naturally Aspirated HP 408 hp @ 85% Duty Cycle USCAR Design 39-Lb Fuel Injector (high impedance) USCAR Design Conncetor Injectors are Packaged in sets of (8) EV6 Connector type $ 360.00 The above calculations assume a fuel pressure of 39.15 psi. If you raise fuel pressure the maximum horsepower numbers will increase. RPM Seris Fuel Injector Wire Harness Adapter Adapts USCAR style harness to JETRONIC/MINITIMER style injector Exclusive Stanless Steel Positive Locking System Packaged in sets of (8) $ 30.00 RPM Seris Fuel Injector Wire Harness Adapter Adapts JETRONIC/MINITIMER style harness to USCAR style injector Exclusive Stanless Steel Positive Locking System Packaged in sets of (8) $ 30.00