You can jump to the 2:30 mark.
More cooling fuel on the Merlin
The 985 even has a rich mixture.
The design of the aircraft engines in most piston aircraft is a rich mixture for cooling the engine, the cylinder in particular - the valve overlap/lead and lag also help with cooling & make for an impressive light show at night! More so if no exhaust is fitted.
Anyone wish to rip the exhaust of a IO-520 and run it at night?