Originally posted by gwshaw
The P-38L had Allisons with the new 12-counterweight crankshaft. Allison cleared them for 3200 rpm/65 in Hg vice 3000/60 for the older 6-counterweight engines. Lockheed seems to have cleared the P-38L for that rating as well, but the USAAF didn't officially do so.
But, it appears much more common for USAAF and to a lesser extent USN/USMC pilots to exceed the official ratings than it was for the RAF or Luftwaffe. In part that was because the USAAF was a lot more conservative with ratings than the RAF was. And also because the much greater manual control required of US engines allowed the pilots do do so with ease. I would expect that it was pretty comon for the L-5 to be running at 3200/65 when it came available.
Greg Shaw
The 12 counter weight crank was developed for the P-82 engines, which combined with the turbo setup on the P-38 would have been real killers.
I think (last time I looked anyway) we have 60" and 3000RPM on the J and L models.
I've seen and heard of Lockheed authorizing as much as 72" on the "dash 30" engines in the L models. I know a few pilots who used it (72" and 3200RPM), and a few who did not. Mostly they said they used it rarely, as in only when they needed it to survive or to run down an escaping enemy. Many I know say they exceeded the RPM limits of 3000, but not so many say they went for 66"-72"+ of boost.
You are correct, to their credit, the RAF would begin pushing to exceed the limits the minute they found an engine was pretty reliable at the lower limits.
The USAAF however did not often do this. This was especially true in the 8th AF with the P-38, as the British fuel did not work well at all in the P-38's, especially the pre J models with the leading edge intercoolers in the outer wings. The mid to late J models and the L's got not only a better intercooler, but a redesigned intake manifold that alleviated much of the detonation issues found in the earlier models with lesser quality fuel.
The fuel situation in Europe was bad enough that Doolittle, who was a Shell employee in peacetime, got Shell to go all out to fix the problems. It was not only a problem for the P-38, but for other planes as well. It just happened that the P-38 "seemed" to be more affected than some others.
We got a hold on a couple of the P-82 Allisons back when I worked on pulling tractors. They were just plain nasty with only the crank driven supercharger. We found out from an Unlimited Hydroplane team that combined with the turbocharger from a P-38 they were just incredible. He 9the machanic for the hydro team) told us he got his from a guy who had a P-38 at one time. It seems the guy with the P-38 tried them, and the Curtiss props just could not deal with the power, they cavitated badly, and became very unreliable. Evidently, the P-38 owner never figured out how to get different props on his P-38.
