Hi Bill,
Most warbirds were originally built to operate on 100 octane fuel.
The Pratt&Whitney 985 Wasp Jr, Wright 975 Whirlwind, etc were much earlier being the genesis of the radial engine period and were designed when 73 and 80 octane were 1930's normal and 100 octane was experimental. See references of the P&W Wasp Jr of 400 hp, 420 hp and then finally 450 hp but for 1 minute for take off only. On 100 octane the max continuous power setting on the 985 is the same as take off power, 36 in hg and 2300 rpm, 450 hp. The engines are low compression at around 6:1 and the blower is fixed gearing with a very nominal maximum manifold pressure and single speeds around 8:1 or 10:1 so the available maximum tapers off as one climbs.
Later, warbird types had higher max manifold pressure, two speed gearing, etc but were still designed around 100 octane. Later and the closing of the war 100/130 and higher were available. After WWII the warbirds like the P-51 and B-25 that were used well into the 1950's in the USAF had their power settings increased as fleet experience and 100/130 was readily available and airliner/transports like the DC-6/Convair 440/L-1049 had their engines optimized and even higher manifold pressures using 115/145 octane. The reason for the high octane was to prevent detonation, and keep cyl head temps down at high power cruise as these airplane's gross weights were increased.
Typically a Packard Merlin and a Wright R-2600 will be able to use normal takeoff, climb and cruise power setting with 100 LL avgas available today. When B-25s were just old airplanes, many were victim of sitting for long periods of time, and when they were operated in the 60's and 70's they were operated with non-detergent oil. Low altitude flying did not require using the high blower, and the clutches would coke up when not excercised. If this went for a long period it was found to be prudent to not shift the blower to high because of the hard deposits from the clutches would break loose and cause lubrication problems throughout the engine. Mustangs are so expensive and their overhaul periods are so frequent the blower shifting operation is frequent and there is very little chance of that happening. Besides typically the fighters are cruised in high blower in the high teens so they can fly fast to their best practical range.
The turbochargers, however, on P-38s, P-47's, B-17's and B-24's are the only type of supercharging I've ever heard of being disabled (besides high blower selection, but still fully operable because it is an internal assembly). This must be what you are referring to. The fuel isn't the real problem, the ability to maintain the high speed, 75 year old GE turbos with their huge turbine wheels and low tech, old fashioned bearing systems is, however.
Much like the idea that the Thunderbolt was a low altitude fighter/bomber by design (it was designed as a high speed, high altitude interceptor in which in was), the Airacobra was a tank buster (it's cannon is way too small to penetrate armor, it was a good low level dogfighter for the Russians), or whatever WWII BS myth someone is spouting, 100 LL avgas is okay for warbirds, airliners need a power reduction all within the charts in the operating manual, and high blower gear selection is sometimes blocked out by operators. Only Turbos have been deactivated because of the reliability of the turbo itself.
Only racers using 2x to 3x the take off manifold pressures need the 115/145 and 160/170 octane fuels available from VP Fuels at the races. It takes a lot of temperature to dissolve those high levels of lead into plasma and even the Packard Merlin would start to foul plugs and if let go longer start harmful lead deposits in the combustion chambers if it wasn't periodically run at full power for a period of time when using more than 100/130 fuel in the 1950's ANG period.
Chris...
I've worked on a number of older warbirds and found that many have had superchargers disabled because of the lack of available high octane fuel. It can be found but is extremely expensive.
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