Matt Karathanas20 April, 2017
You’ve spent hundreds, maybe thousands of dollars upgrading your engine. You’ve dedicated hours and hours of work and research to determine what aftermarket parts will give you the most horsepower gains. Now, what about fuel injectors? If any engine components or bolt-ons are being added, it’s probably a good idea to make sure you have the appropriate fuel injectors for your engine.
This goes doubly so for any components designed to increase airflow (intake, throttle body, turbo, etc.), as it is important to address fuel flow so that it is always matched to the airflow requirements of your engine. Increased airflow requires increased fuel flow to maintain a desired air/fuel ratio (AFR). But how do you know what injectors you need?
There is a rather simple equation to determine the appropriate fuel flow for a given engine. You will need to know your desired horsepower, BSFC, and duty cycle. First you must divide your desired horsepower output by the number of cylinders. Then divide the BSFC by duty cycle. Multiply the results, and you’ve got your ideal fuel flow rate. See the examples below.
(Desired HP / # of Cylinders) x (BSFC / Duty Cycle) = Flow Rate
Example 1: 700hp 8-cylinder engine, naturally aspirated
(700 / 8) x (0.50 / 0.80) = 54.6875 lbs/hr fuel flow
Example 2: 800hp 8-cylinder engine, turbocharged
(800 / 8) x (0.65 / 0.80) = 81.25 lbs/hr fuel flow
Glossary of Terms
BSFC (Brake Specific Fuel Consumption) | A measure of fuel efficiency, it is the rate of fuel consumption divided by the power produced.
Duty Cycle | The amount of time a fuel injector stays on, or open.
Typical operation is 80%.