Between March 42 and November 43 the Merlin company wanted increase performance and run time capability of Merlin engines. The test was 3000rpm and max boost for the given engine. In the beginning it was 1 hour continuous along with take off load tests. Then by mid 43 it was a 50 hour test with a Merlin 66 3000rpm 18boost. Then before the end of November 1943 a 100 hour test at 3000rpm 18 boost.
The engines along the way had problems and ultimately strengthened to achieve the 1943 100 hour test. Oh, and the final 100 hour test engine was then mounted into a spitfire for another 100 hours of testing. This is where a 200 hour Merlin 66 test reference comes from in some documents.
Here are the components that had to be strengthened: Crankcase, main bearings, end oil feed crank shaft, and deep top land pistons.
Republic did an 8 hour run at WEP on a stand with an R2800. Then mounted it in a P47 and ran it for 110 hours as a test plane. Military engines could be run at full rpm and boost for long periods continuously. WEP and other running limitations were to extend the useful life span so you were not consuming engines and needing replacements which on many fronts during WW2 were a scarce commodity.
While a piston engine aircraft is on the ground sitting or taxiing, isn't that the hardest time on engines due to not having enough air flow to cool the engine? And so would require the greatest attention to engine management settings? Used to fly with my father at times when he flew cargo in a Beech 18. He was most worried about engine management and over heating while on the ground since it had two radial engines.
