from another post :

"The VAFC takes the voltage output from MAP sensor and modifies to add or subtract fuel. You can't really add fuel with a V-AFC in a boosted application as that is adding voltage which essentially shows the ECU boost. To add fuel in a boosted application you need to crank up the FMU and then use the V-AFC to remove that fuel in places where it is not needed."


My question is - if I dont plan on upgrading any fuel components that come with the Comptech kit, is a vafc necessary for proper tuning? It sounds like the vafc will accomodate for WOT rich a/f, and thats all. Yeah, it can change the vtec xover, but it seems like the 6000 spot is found to be best. I was only planning on going with the vafc so Im not running dangerously lean, and to get another 5% power out of a dyno session once everything is installed. I will be installing an simple a/f gauge, but that doesnt seem accurate in all circumstances. Any help is appreciated, thanks

Rob

 

I think the post that you cited explains it pretty clearly. The FMU aparently doesn't offer the fine tuning capability that is needed to optimize air / fuel ratios. The FMU would be used to make sure that it doesn't run too lean anywhere in the RPM range, then the V-AFC is used to remove the extra fuel where the FMU overcompensated.

 

I got it, thanks