Forum » Understanding AFR » Calculating de 2,5% variation on fuel copensation.

Calculating de 2,5% variation on fuel copensation.

Understanding AFR

Discussion and questions related to the course Understand AFR

= Resolved threads

Page 1

Hi Guys!!

Been trying to get to the 2,5% for every 10ºC. But I always get do something close to 3.

Since the formula for air density is p=P/RT and considering the same pressure ir we vary te temperature from 0ºC to 10 ºC will vary the Kelvin temperature to 273 to 283, wright?

If my calculations are wight, we would get to something close to 3,6%.

Where did I get this wrong?


Ricardo Campos

I apply a little rounding here along with some experience with how engines actually respond. I find that if you use the specific corrections as calculated you tend to over compensate and go leaner as the IAT increases. 2.5% has worked pretty well for me but you also need to understand that it's only a starting point. There are many other factors that will affect the compensation since we're measuring air temperature at the sensor rather than charge temp as it goes past the valve (which is what really counts).

As Andre said, it isn't a pure relationship - the air in the charge will be picking up heat all along the intake tract and even inside the cylinder - this will skew the actual values against the theoretical.