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Being "past its prime" is the whole point of trying to improve performance in the first place.By the time the G models were running on the test stands the P-40 was not only past it's prime, it was beyond "stick a fork in it, it's done". It was throw the scraps to the dog, done...Upping the compression ratio is definatly the WRONG way to go if you are looking for power and not economy.
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1. The single stage supercharger just doesn't work that well over 20,000ft now matter how many gears or what gear ratio you use or drive it with. The late model Allisons used higher pressure ratios at take off than the early versions (mainly becaue they could use improved fuels), the -73 vesion in P-40K ran at 51in of boost for take off and 1325hp and 60in of boost at war emergency for 1550hp at sea level for pressure ratios of 1.7 and 2.0 respectfully. going to even 20,000 feet at those power levels means you need pressure ratios from your supercharger of either 3.4 or 4.0. The higher the pressure ratio the more power it needs to drive it AT ALL altitudes and throttle settings. Two stage superchargers can give the same pressure ratios with less power input and less heating of the intake charge. Or even more boost for the same drive HP.
Not necessarily. Higher altitude performence can be gained at the COST of poorer low altitude performance if you use a larger impeller. I now believe that the engine change wasn't necessary so much as putting one production line to work making "Interceptor" Hawks built for high altitude supercharging and maximum weight savings for rate of climb wherever they could get it.
Thus my suggestion for the adapting a second gear to the existing supercharger setup.That may be true but how much low altitude performance do you want to give up?Clay_Allison said:Higher altitude performence can be gained at the COST of poorer low altitude performance if you use a larger impeller. I now believe that the engine change wasn't necessary so much as putting one production line to work making "Interceptor" Hawks built for high altitude supercharging and maximum weight savings for rate of climb wherever they could get it.
You still have to take-off and climb to combat altitude.
Some of the later P-40s did trade 125hp at take-off for an extra 100 or so hp at 20,000ft. if you want several hundred HP than that several thousand feet higher then you are going to loose several hunderd more HP at sea level. Take- off and low altitude climb using less than 1000hp isn't going to impress too many peaple.
Thus my suggestion for the adapting a second gear to the existing supercharger setup.
This way you don't loose anything down low and gain some up on top.
Bumping the c.r. only aids overall engine efficiency across the engine's entire powerband, but my main point (before bringing up the c.r. issue) was that the addition of a second gear would help the plane perform better at altitudes above 12K-15K feet.
Elvis
...something else that just struck me, but I've heard from others in the past.
What if a two-speed/two-stage S.C. were added to the Allison? (I'm thinking about the "-81" and "-99" engines, in this particular case)
Would that be a more "compact" system than re-installation of the turbo that was used in the P-38?
Elvis