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I was curious of what the top speed of the P-47 would be without wing pylons. I found that the Fw-190 found a 8-10kph increase in speed with the removal of its ETC 504(Which is located under the fuselage. By using common sense, it would only make sense if the P-51 had a better increase of speed because the Mustang has 2 pylons under each wing of roughly the same size of the Fw-190's ETC 504. I found a 20kph increase in speed with the removal of the P-51B's pylons. So knowing that the P-47's pylons are nearly 3 times the size of the P-51's pylons; what would be the speed increase if we were able to remove the pylons on the P-47. Or are all tests on the P-47 completed without wing pylons.
Thanks
The P-47s built with a larger 'C' series Turbo — which entered service in 1945 — could maintain 2800 bhp up to about 32,000 feet. However that rating was just an official safety limit approved by the USAAF. With more advanced fuels and additional ADI fluid, the R-2800 engine, including the older 'B' series, was capable of producing higher boost pressures and more power:
" An interesting footnote in the development of the R-2800, during World War II Frank Walker was charged with the task of testing the ADI system developed, in an emergency, for the R-2800. During the same time period Pratt Whitney was testing early development versions of the R-4360. Frank regarded the R-2800 as his baby and consequently wanted to prove to the world there was still life left in it. He made it a personal goal to keep up with the power output of the R-4360 with "his" R-2800. When reports came through that 3000 horsepower had been achieved with the R-4360 he met that challenge by boosting the R-2800 to ever higher manifold pressures and feeding it additional ADI fluid. With these changes, Frank met the 3000 horsepower challenge.
Then the R-4360 reached 3500 horsepower. No problem, Frank ran his R-2800 up to an amazing 140 in. Hg manifold pressure and fed as much ADI fluid as the engine could tolerate. Again, he matched the R-4360s 3500 horsepower.
When the 3800 horsepower threshold was achieved by the R-4360, Frank ran his R-2800 to a stratospheric 150 in. Hg to match the 3800 horsepower benchmark. However, Frank had to call it quits at 3800 horsepower; it would have been a difficult explanation to make to his superiors if he had blown up his R-2800 in the test cell.
What makes this story even more remarkable is the fact that Frank's R-2800 was a lowly "B" engine! And as Frank found out, not unnaturally, there is no replacement for displacement. Even so, for a while he gave the R-4360 and its development team a good run for its money. It would be difficult to imagine this kind of friendly rivalry and comradery in today's corporate, "design by committee" environment.
As a further endorsement of the R-2800's sound and rugged design, Frank made regular test runs of 3000 horsepower for one hundred hours."
See p.218-219
White, Graham. R-2800: Pratt Whitney's Dependable Masterpiece. SAE International, 2001.
The post above, from the US government, indicates that the R-2800 produced 2840HP with 70 in. Hg of boost. That implies that the R-2800 would require about 110 in. Hg of boost to produce 3800HP.
If you refer to P-47D AAF No. 42-26167, the USAAF engineering report for 70" Hg @ 2700 rpm indicates 2840 bhp at 10,250 feet and 2790 bhp at ground level. The chart does not indicate if the numbers are specific to the engine installed, or generic figures based on previous testing.
Frank Walker's R-2800 was run on a test stand at Pratt Whitney. I know where the Turbo is on a Thunderbolt but I have no idea how Walker set up his boost system in a shop environment. It was not explained by the author. Presumably, the test engine was not spun higher than the usual limit of 2700 rpm to obtain readings. I don't understand how you calculated for the possibility of 3800 bhp at a lower manifold pressure than 150" Hg, so I can't comment on that score.