Originally Posted by
Anilv
I seem to remember reading about RR scuppering work on other engine types on the basis that all resources should go towards improving the Merlin. I believe one casualty was an engine by Napier.
I don't think history supports that. RR were developing the Merlin and Griffon side-by-side and only abandoned the Peregrine because there was little point in developing the last stretch of a 21Litre Kestrel V12 when they had a better 27LitreV12 (the merlin) which had both more power and more growth potential - it might have made 1200bhp but there was no demand for such an engine. They also abandoned the Vulture and other X-configuration engines because they never did find a solution to the problem of lubricating 4 big ends on the same crank pin at very high power outputs. This didn't stop them following Napier's lead and producing the H-configuration Eagle II, whose twin crankshafts (and thus only two big-ends per crankpin) circumvented the lubrication problem, alongside the Merlin and Griffon.
The engine they DID abandon despite it's evident potential was the 26litre V12 2-stroke Crecy - an engine that could have delivered a Spitfire limited only by Mcrit (~500mph) with 3,000bhp plus 1200lbs of direct exhaust thrust being a very realistic possibility. But the Crecy was mainly abandoned simply because jets were already in development that offered even better performance.
Of course Napier spent pretty well 100% of their effort tinkering with the potentially superb but flawed Sabre. The shear amount of time and effort dissipated in their tinkering was a serious issue at a time when war-survival needs demanded efficient use of all resources. There was a point when they were threatened with compulsory nationalisation and being handed to Rolls Royce (who were a "trusted pair of hands") if they didn't get their act together. But I digress.
On the point of the original question - in the limit a liquid-cooled engine can always be run at higher specific power outputs than an air-cooled one because of the finer control over the thermal dynamics of the internals. High-power air-cooled engines need to have wider fits and clearances when cold to allow for the poorer control of running temperatures, which is one of the reasons why they often belch so much smoke (burned oil) during start-up and warm-up compared to liquid-cooled ones
£0.02 supplied,
PDR