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This isn't hard to believe, because we can all document this is the case with the entire P-40 series, none of them have their maximum, say for the 40E 1470hp factory rated war emergency rating, they all have the "military rating" of 1150hp printed.
I think we have several things going on here.
1. What is WEP for different countries and times?
Foe instance before WWII the American P&W R-1830 was rated at 1200hp for take off but only 1050hp at max continous (or climb) there was NO military rating let alone WEP rating. Some earlier pilots manuals show a military "EMERGENCY" rating equal to the take-off rating for some engines. This is equal to the 'later' military rating but not WEP.
The R-1830 was allowed to use the take-off rpm and boost levels for "military" power but never received a WEP rating which would require even higher boost. Engines were rarely allowed to over rev to reach a WEP rating.
Given the problems in translating documents and the changing definitions of some terms (many engines had an 'international' rating before WWII, this rating disappeared postwar) I can fully believe that some Japanese planes were rated at max continous power and not at take-off or " military" power while having no WEP rating.
Please note that ALL British climb specifications are for max climb power and not max 5 min power.
I could be wrong on the Japanese engines but since different countries did measure performance in different ways or under different conditions trying to compare them gets tricky.
I have one book that gives the top speeds of many US Navy fighters at max continous power,quite a change from max power
Now if anyone can read Japanese I do actually have documentation from Nakajima factory listing complete specs on all their wartime engines. I can't read it, it's like a 30pg scanned book one of the Japanese enthusiasts I've been talking about emailed to me.
The one I think is the Sakae-12 says maximum normal power is 1100hp/2700rpm at +200mm (38"Hg) boost in low blower at 2550 metres altitude and 980hp/2700rpm at +200mm boost in high blower at 6000 metres altitude. It says the maximum war emergency power is +300mm (42"Hg) boost in low blower only (ie. at take off and under 5000ft or thereabouts only, presumably for carrier take off) is 1130hp/2750rpm/full rich.
Hey none of you can read Japanese can you?
The one I think is the Sakae-21 says 1220hp high blower and 1440-1500hp possible in low blower, same settings as the Sakae-12. I mean their only other 14-cyl radial has 1650hp so that can't be it.
I keep finding more stuff. Note that also Wright engineering dept. did an full tear down of a Kinsei 14-cyl radial (lower powered than Sakae-12, fitted to A6M1 original prototypes), they rate that engine for 850hp max climb and 1050hp for max take off. Surely the Sakae 12 is higher than that, by any convention, the Sakae made production versions for that reason (and two blower gears), but the USAAF initially rates the Zero-21 as worse than this engine stock specifications. That's in error, it definitely is.
But A6M1 had Mitsubishi Zuisei 13 not Kinsei. It had a smaller capacity compared to Sakae (contrary to Kinsei).I keep finding more stuff. Note that also Wright engineering dept. did an full tear down of a Kinsei 14-cyl radial (lower powered than Sakae-12, fitted to A6M1 original prototypes), they rate that engine for 850hp max climb and 1050hp for max take off. Surely the Sakae 12 is higher than that, by any convention, the Sakae made production versions for that reason (and two blower gears), but the USAAF initially rates the Zero-21 as worse than this engine stock specifications. That's in error, it definitely is.
Aviation Monthly, who did a full spread on the BMW 801 and DB601, it was really cool, stripped down to the bearings. Those roller bearings on the Daimler by the way are seriously trick, that's like a modern 25-grand race engine, no kidding.