Very interesting, and thanks.
So, we now have a case for both the Pennine and the R-R Crecy, as potential 'greatest ever piston engine design'.
We will have to see what the other knowledgeable folks out there feel.
The concept behind the Crecy started with Harry Ricardo, and it was to be a compression ignition engine, ie a Diesel. Around 1930 a lot of manufacturers were playing with Diesels because of poor fuel quality causing problems with petrol engines. It was as a Diesel that R-R started work on the Crecy, using one of Harry Ricardo's test engines.
Later in the 1930s the fuels had improved, and the idea was floated that the Crecy be developed as a short endurance high performance petrol engine. The Crecy used direct fuel injection with a chamber designed for a stratified charge. The intake air was pumped in through the ports in the lower part of the sleeve, the exhaust exited through the ports in the top of the cylinder - the sleeve didn't have ports for the exhaust, but the top of the sleeve uncovered the ports. The exhaust ports covered the entire circumference of the cylinder.
8 V2 test engines were made (they chose V2 so they could test the sleeve drive mechanism), and 6 main engines (V12 Crecys). Maximum power extracted was 1800hp at the power take off, or similar to what the Merlin was making on the bench at the time. It was expected that exhaust thrust would be equivalent to 30% of engine power. Fitted with an exhaust turbine to recover exhaust energy the power was around 2500hp. Problems with melting pistons were not overcome before the program's cancellation.
Ricardo continued to devlop his single cylinder engine, and managed to produce the equivalent of 5000hp in a Crecy.The Rolls-Royce Crecy
, from the RRHT (I'm sure I didn't quite pay that much for my copy!).
The Pennine was essentially a larger, more useful, version of the Rolls-Royce Exe that was built before the war. The Exe was an X24 cylinder aircooled sleeve valve engine. The reduction gear on the Exe was a simple spur gear type. The Exe was 22l (1350cid) in capacity, about the same as the V12 Kestrel and Peregrine. And it was more powerful than either, nearly as powerful as the Merlin of the time. It was heavy, however, and the small capacity worked against it. It flew around in RR's test hack for some time, quite reliably.
IIRC, the Exe was designed by AJ Rowledge when he was recuperating from illness.
Other versions of the Pennine were envisioned. One with a larger bore which took capacity out to 75l, an X32 version of the standard bore engine which gave 61l, and an X32 with the larger bore at over 100l.