EFI Fast facts

January 05, 2015, NASCAR.com

A quick guide to electronic fuel injection as used in NASCAR

In the past, Sunoco Green E15 mixed with air to power the engines at the carburetor. But with electronic fuel injection (EFI), that process changed. Now, multiple-port EFI injects fuel into each "intake runner" and mixes it with air. A combination of sensors and a Freescale/McLaren ECU (Electric Control Unit) makes the engine more efficient.

EFI: The setup
Laptop computers help crew chiefs and engine technicians read data provided by the ECUs before the race. During the race, the fuel injection system technology adjusts itself, eliminating the need for teams to monitor the data.

EFI: Restrictor plates
NASCAR requires EFI engines to use a restrictor plate at Talladega and Daytona. It is placed beneath the EFI throttle body and limits the amount of air available to the engine. Unlike carbureted engines, Sunoco Green E15 will not pass through a restrictor plate opening.

EFI: Key parts/partners

1. Freescale/McLaren Electronic Control Unit (ECU) -- The brain of the EFI system receives data from sensors to determine the amount of fuel to inject into the engine and when to fire the spark plugs.

2. Holley EFI throttle body -- The only thing passing through the Holley EFI throttle body is air, despite being similar in appearance to a carb. Four air valves are actuated by stainless steel throttle shafts, throttle levers and linkage designed for the extreme NASCAR racing environment.

3. Bosch O2 Sensors -- These sensors provide the ECU with key data so the system can adjust the air/fuel ratio to maximize horsepower and engine performance.

4. Other sensors -- A network of sensors provide the ECU operating information at a rate of up to 100 times per second.

5. Fuel injectors -- Each cylinder has its own injector that precisely sprays Sunoco Green E15 into the engine for ignition.

6. Ignition coils -- Eight individual ignition coils send electricity to the spark plugs making distributors obsolete.

7. Spark plugs -- Use electricity from the coils to ignite the Sunoco Green E15 and air mixture.