Sorry guys, I stand by the"nope" as the original question was.
How did British poppet valve or traditional (non-sleeve) valve radial aero engines compare to those of other nations?
Now perhaps I did infer a point in time of the late 30s or later from the "(non-Sleeve)" part of the statement
and
Was there any hope for British non-sleeve radial engines?
Pretty much eliminates Kestrel, Merlin and Griffon engines from the discussion as they are
not radials.
The Jupiter was great engine of the 1920s (and definitely pre sleeve valve) and was built under licence in 17-18 countries and maybe more.
However it used 146 X 190mm cylinders (or imperial equivalent) and as such was the direct ancestor of the Bristol Pegasus.
Bristol (meaning Fedden) started work on the Mercury in 1925 to replace the Jupiter and the short stroke Mercury allowed for higher RPM and smaller diameter. In 1927 they went back to the original stroke for the start of the Pegasus.
The Alvis engines were based off of Gnome Rhone engines which in turn were based of the Jupiter engine (they all used 146mm bore cylinders) which is one reason the ALvis engines went nowhere. There were others including perhaps politics.
The Mercury was a very fine engine for a 1520 cu in/ 24.9 liter engine but that size was just too small for the commercial aircraft market of the late 30s and the military market of the late 30s and WW II. Many Mercury's were built and used but
most planes powered by them were quickly moved to less than 1st line combat roles. Now the same could be said for the P & W R-1535 14 cylinder two row radial as it was quickly supplanted by the R-1830 (30 liters) and P & W refused to do any more development work on it. P & W also pretty much stopped developing the R-1690 Hornet (27.7 liters) in the late 30s because it was too small and also competed with their own R-1830. Don't forget that P & W started work on the R-2800 (45.9 liters) in 1936/37.
Wright was not only doing major work on the R-1820 (29.8 liters)( a number of generations of the engine that had little or no parts interchangeability from generation to generation) they were also working on the R-2600 (42.6 liters) and R-3350 (54.9 liters) (which had to almost start over again in the early 40s)
A 14 cylinder Mercury would have been 38.7 liter engine.
Perhaps Snowgrouch can answer this question much better than I can but it seems to me (and I could well be wrong) that the Bristol 4 valve cylinder head was a bit less than ideal.
Yes it had 4 valves, yes it had a pent roof (or at least sort of ) combustion chamber but the actual valve and port layout was bit odd. Instead of both inlet valves being on one side or slope of the pentroof and the exhaust valves on the other side or slope the Bristol engines put one intake valve and one exhaust valve in each side or each slope. I don't know if this hurts the gas flow or has no effect?
In any case as mentioned elsewhere the big American radials used Hemi heads or darn close to it with big valves, large angles and large ports leading to and from the valves.
In fact even some American trainer engines used some pretty good head design for the times.
The 4 valve heads on the Bristol engines
may have interfered with getting enough cooling fins in the head area?
The Deerhound may have worked, it might not have, I have no idea but it was 1-2 years away from production. The Deerhound I was 37 liters the Deerhound II was 42 liters and the Deerhound III was even bigger. Which basically means it was still in early development.
By the mid to late 30s the British poppet valve engine was in sorry shape development wise, however well the individual engine designs served in the first few years of the war. The potential was too little and promised to be too late had anyone wanted to shift back from sleeve valve engines.