kool kitty89
Senior Master Sergeant
If that was a V-1710-33 pushed to 3400 rpm on standard 100 octane fuel and 75" MAP, that would seriously imply the detonation limits with that supercharger weren't as extreme as Allison's documentation later implied with the 9.6:1 engines. A 7.48:1 ratio engine would be running too slow at 3400 RPM to push 75" at SL, but maybe there's more context here or it was an 8.1:1 supercharger used? That or the 75" MAP and 3400 RPM runs weren't used in conjunction.Ho Kool Kitty,
I worked at an Allison shop for about 2 years and it is VERY possible, standing still on the ground, mounted to the back of a Ford truck, with a Hamilton Standard club prop. Gen (Ret) Davey Allison came by several times and told us how he sold Chenault on the P-40. It involved demonstrating it at 75" MAP. When you did that, the P-40 sort of "woke up" and flew just great, according to General Allison.
Gen. Allison mentioned 3,400 rpm as his demo setting. He passed away about 3 weeks after his visit and we were glad we had an Allison ready for test that we could let him start up and help break in. Out break-ins were generally about 4 - 8 hours at 1,200 - 2.700 rpm and idle upo to about 48" or so.
Pushing 3200 RPM at 75" MAP without ram would result in something close to 1800 HP at SL with the -33 going by the chart on Peril's site (and approximating the 3200 RPM curve). I could see that sort of strain being used for demonstration purposes, but if the AVG ever used that as emergency power on their P-40Bs it's no wonder they stripped reduction gears and burned through engines. There's obviously a ton of middle ground between the conservative military rating used by the USAAF and full-out overrev AND overboosting especially on those early engines.
With that sort of engine abuse, those P-40s would have been screaming at low altitude, though and should have smoked Spitfire Mk.Is and IIs in WEP ... or Mk.Vs for that matter. (might have nearly matched Spitfire Vs in altitude performance with that overrev -plus the P-40B being substantially lighter than later models) Using overrev only at altitude would have been a lot easier on the engines too.
If it genuinely had been acceptable to overrev the engines for WEP as routine, then the 8.8:1 supercharger ratio wouldn't have been that big of a limit either and both the backfire screens and kink/bottleneck in the intake manifold would have been bigger priorities for supercharger efficiency improvements.