what does the VAFC do exaclly?? i now it gives you more hp and connects to your ecu?

 

It lean's out the air to fuel (A/F or AFR) ratio. There is an ideal mixture of air to fuel which will generate the most power. There are many factors that impact that exact ratio, including gasoline additives, combustion swirl, etc. It's preferred to get as close to that ideal mixture without going over the threshold and running too lean, which can damage the engine. Car makers therefore set the A/F very conservatively to protect the engine from variations that might lead to a too lean condition...also, running rich allows unburned gasoline to coat the cyl walls and help with cooling, which also increases engine life.

But usually the manufacturer settings do not maximize power.

The VAFC corrects the ecu's imputs by a set amount at pre-determined RPM increments and forces the ecu to believe it can lean out the mixture. A good tuner can get a few more hp out of the car but leave enough of a buffer to ensure the risk of engine damage is low.

 

VFAC can also control vtec engagement point. many people choose to lower vtec a few hundred rpms, so it kicks in at maybe 5500rpm instead of ~6000 rpm.. based on your setup, this can give you some more ponies in that small range.