Here is a pic of the data plate from the Dyak engine at Mascot, Sydney, AU

DB CR’s

There is a direct reference to this matter in a report that was written by Rolls-Royce engineers following a visit to Germany shortly after the end of the War.
The DB engineers they spoke to made two points, 1/ that they were required to build their V-12 engines inverted even though it was against their better judgement and
2/ the use of the differential CR’s in the DB 600 engines was to combat the effects of uneven oil consumption in the two banks of cylinders.
The different CR’s had NOTHING to do with off-set superchargers or articulated con-rods (which these engines never had).
Read the posts by TempestNut – he knows what he is talking about!!

RM numbers

I think I understand. The Merlin 30 and 32 had reduced size impellers, presumably for better performance at lower altitude, but they are not called cropped because the engine was designed to have them. The Merlin 45M has a reduced size impeller which is called cropped because it is a modification to the Merlin 45.

In M&S there is a table of engine variants. One of the columns is headed MoS Experimental Nomenclature. Can you explain to me what is in this column. MoS = Ministry of Supply? The entries all begin RM for Merlins and RG for Griffons – Rolls Royce Merlin and Rolls Royce Griffon? What do the numbers that follow refer to? The size of the supercharger? Somebody told me that the cropped series 45 and 50 Merlins (M suffix) were not given RM values because they were modified engines but M&S list values for all the variants except the Merlin 66-68. Is this another mistake by M&S.
Many thanks.

The numbers after RM or RG refer to the RATINGS for the particular type of engine, eg ‘3’ means the third attempt to provide a particular performance standard for that engine.

DB 600 series differential compression ratios.

Attached is a copy of page 4 of a 6 page article I did on this topic some time ago.
This particular page quotes the only concrete reference I’ve ever come across pertaining to the matter.
The different CR’s were introduced because of an OIL CONSUMPTION problem, not off-set supercharger or articulated con-rods (which the DB 600 series engines never had).