Red Bull boss Christian Horner has called for a rethink of F1's engine penalty rules after nine of the 20 drivers taking part in the Italian Grand Prix were hit with grid drops on Sunday.
Under the current regulations, each car is allowed to use four full power units per season before it starts incurring penalties. The power unit itself is divided into six individual elements -- internal combustion engine, turbocharger, MGU-H, MGU-K, energy store and control electronics -- all of which can result in a grid drop if a driver exceeds a tally of four for the year.