acascianelli

Inside each intake runner on the 3V 4.6L (I believe the 4V 4.6's have them too) there are butterfly valves that will restrict airflow to the cylinder. The purpose of these valves is to get better fuel burn and they also help with low end torque. At around ~3000rpm under WOT, these valves open up to allow full flow through the runner. Even when the valves are opened, there is a small cross-section that still block some airflow. Eliminating these valves altogether is thought to free up a little power in the higher revs because of the increased airflow. If you remove the valves, you can expect a little loss in fuel economy and possible a loss of low end torque. Some tuners have been able to tune that out, and other people just install them at the same time as a complementing mod such as a UDP or headers to make up for the loss. A tune is required for delete plates because it recalibrates the engine for the extra air when the valves aren't close, and it will disable the motor that actuates the control valves.