wmaxt:
WEP is often a throttle position that allows more power to be used. This position is presumed to be detrimental to engine life esp if it is used for more than 5 minuets.
Yes, on aircraft engines the rules change there, too hard for me to explain now, though someone else here might be able to?
Otherwise, running an engine hard is always going to shorten it's life.
The Tumansky turboprop for e.g.
The detramental issue might be overboost,
Unlikely, it's a switch usually so is deliberate.
They can grenade an engine though.
over revs (I've read that the extra force on con rods increased by 6 times with a rpm increase from 5,000rpm to 5,500rpm),
Yes, though if the engine is hand-built this shouldn't be too much of a problem?
This could be because of a lean mixture at WEP and/or high revs?
From the sound of things the Allison shouldn't have this problem?
Depending on the peace/war situation a limit on total hours was placed on an engine before mandatory replacement/overhaul. Interestingly the manufactorures tested Allisons to 2,300+ hp @ 105+ boost and PW ran the 2800 to 3,000hp( from memory does anyone have the right numbers handy?) range for 250hrs without trouble the numbers the AAF ran are substantialy lower.
Taking this into account, it is IMHO likely gonna be a NO2 problem causing a lean mixture, though:
1. Was NO2 even used?
2. The rules are different when in the air.
As for cam shaft timing for low rpm (>3,000rpm)emgines, tight overlaps are normaly used which would preclude cam timing as a problem.
Yes, they are nowdays, but what about then?
However with a supercharger to compensate, the cam timing becomes far more flexible, so, maybe.
A supercharger can cause/aggravate things like valve bounce or even force the valves open on poorly made/designed valve springs, this might be something?
Lunatic:
It should also be noted that (contrary to someone elses comment) that generally speaking if a 2 stage supercharger is being used the gearing not the staging is what changes with altitude.
I've heard that too, though I may have misread?
Another option is the variable-speed mechanical supercharger, which uses a fluid coupling to vary the speed of the 1st stage of supercharging as was done on most Bf109 variants. This has the advantage of allowing higher power over a wider range of altitudes, and minimizes power lost off the crankshaft. However it has the disadvantage of wasting power at all but the unit ratio (1:1 on both sides of the coupling) and as the fluid in the coupling heats (especially as it slips) the unit becomes less and less efficient.
Interesting, was that like a viscous coupling?