×

Sale ends todayGet 30% off any course (excluding packages)

Ends in --- --- ---

# Fuel Flow Based On Air Flow

### Tech Articles

Discussion and questions related to the course Understanding AFR

I am trying to figure out a formula to calculate fuel flow in L/h that takes into account theoretical air flow calculated from number of cylinders, valves per cylinder, displacement, and theoretical VE that cam profile will provide. Then calculate the fuel flow based off the output of the aforementioned formula, and adjusting based off of WOT Lambda target.

Does anyone know how to calculate that?

In theory, it's possible to do it, but I don't think you've quite grasped the degree of difficulty involved.

For example, regarding VE (the real use of), the valve arrangment isn't required as that will come under the airflow numbers for the head being used, the camshaft breathing characteristics will change through the rpm range (why torque curves aren't flat), induction and exhaust designs and limitations will also affect overall VE.

In practice, you will only be able to make a rough approximation and will need to fine tune it on a dyno'. You cannot tune effectively by using a specific lambda 'target', because different engine combinations may work best with different values. It's easy to throw away 10%, or more, giving the engine what you think it should get, rather than what it actually wants. You may luck out and hit it just right, but the odds aren't in your favour.

Hi Gord,

Thank you very much for the response. Your answer makes perfect sense. My intention is not to use the calculation to specifically tune an engine. I am trying to model fuel flow requirements for a application using theoretical airflow calculations instead of relying on BSFC. I have heard on here and other places that BSFC is very error prone and shouldn't be used to estimate the size of the injectors or fuel pump for an application. Is that assessment correct or am I misunderstanding?

Just trying to figure a reliable way to calculate what I will need when I am building my Rally cars.

We usually reply within 12hrs (often sooner)

#### Need Help?

Need help choosing a course?

Experiencing website difficulties?