Discussion and questions related to the course EFI Tuning Fundamentals
Hello, you have mentioned before that air ratio for fuel is 14.7 (1.0), why did you change it, is it okay to run richer in order to get better results (POWER)?
So in this case, is it okay to go up/down more than the standard ratio (14.7)? sorry for this noob question
14.7 is the stoichiometric ratio where you get complete combustion. It also happens to be where you have a balance between power and emissions. If you go leaner to say 1.05 lambda you will get better fuel economy but less power. This lean mixture will increase your cylinder temp raising you NOx emissions and reducing the amount of timing advance you can safely run. If you go the opposite direction and richen your mixture to say .85 lambda you will generally see better power but less fuel economy. This rich mixture will decrease you cylinder temp, creating a denser charge and allow you to run more timing advance. however you will see an increase in HC emissions. These are just general numbers though, each engine is a little different in the AFR they are happy with, but in general if your aim is to make more power you will want to richen your mixture from 14.7.
The AFR we chose to run will depend on the current load being placed on the engine. At idle and crusie we generally want good fuel economy and minimal emissions so a target of 14.7:1 is common. As we increase the throttle and hence ask for more power from the engine we target a richer mixture in order to make sure we make maximum power, and also to ensure we supply some extra fuel to cool and control the combustion chamber. For an N/A car this might be somewhere in the region of 13.0:1 for example.