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Was the R-2800 really so super-engineered, or the graph from the book is wrong?
The R-2800 was not any more engineered than other engines but probably well suited for a war time airframe of that era, although use of the R-2800 continued on airliners well into the 1970s.
The introduction of 150/100 gas and water injection allowed higher outputs.
Its also a relatively large radial engine that lent itself well to water injection and high manifold pressure, however even with out an ADI system, the R-2800 still produced 2000-2100 hp with 130/100 gasoline.
Consistency also depended on turbo/supercharging which would also contribute to changes in full throttle height.
The engineering of the engine to handle water injection also took time to develop and understand, mostly dealing with changes in timing and engineering of inlet parts to handle higher pressures. The basic engine was still the same though changes from variant to variant probably differed depending on use, such as parts engineered for turbo or supercharging, reduction gear ratio, prop disc, endurance....etc.
I've only seen a handful of charts that deal with the subject of water injection. They all differ depending on the day the testing took place. I would not question whether a chart is wrong, but what the conditions of the test were and most publishers fail to or lack those details when they choose to include charts.
Bill