Hi Pete, I recall (getting older now….) a RR engineer on a programme long ago, possible Robby Coltranes trains planes and automobiles featuring black 6, who on being asked about the DB601’s multi-point fuel injection efficiency vs the single point on the later Merlins, stated that as it was injected into the eye of the supercharger (Merlin), the increased charge density resulting, was much more efficient than when directed at the inlet, evolving much more power and efficiency as a result?

Any ideas?

Yes, putting it simply, the fuel in the mixture evaporates as it passes through the supercharger and cools the charge quite significantly, like an intercooler. The result being you get more fuel air mixture into the cylinders for no more effort on the part of the supercharger, cooler mixture takesup less room, effectively. This is one reason why the DB601 is a larger displacement for the same power output as an early Merlin, combined with a less efficient supercharger. That’s not the whole story though, because the DB fuel pump is very efficient and the engine contains an amount of magnesium, making it no heavier than the Merlin. They were very closely matched around 1940.

Pete