Stuart, please read your sources again on condition of typical eastern front airfield (be it German or Soviet).
Conditions on average eastern front airfields were way worse including horrible amount if dust during summer and way lower temperatures then in west Europe during winter.
1st one killed filters and carburetor quickly, low temperatures played hell with rubber seals and even if aircraft survived winter it would start leaking as soon as temperatures raised again, or worse as soon as it warmed enough after starting engine...
There was also large lack of spare parts of any kind (both with Germans and Soviets) due the problem of regular delivery to frontal airfields due the distance involved (and partisans in German case). Sometimes units would be low on ammo and only some of aircraft guns would be loaded (Germans often did not load outer 20mms on 190), or short on bombs when local armorers would improvise from captured bombs or adopted captured mortar/arty shells. Both happened often in 1944. on Soviet side as amount of ammo used during Bagration was staggering. At one moment there was a prohibition of strafing ground target by fighter units, situation with ammo delivery being that bad...
Bojan, Im not as ignorant of conditions on the Eastern Front as you think. It got dusty, I know, but is there any reason why tropical filters couldnt have been improvised? They could have asked the RAF to have supplied them with that mod if it was such a problem. It got cold, well yeah Im perfectly aware of that too. The Me109 would have had identical problems to Merlin engined airframes, and whilst the solutions were dramatic (huts, lighting fires under the airframe etc) there is no evidence to my mind similar methods couldnt have been similarly improvised for Western supplied aircraft.
The spare parts also is a fair point, but why wouldnt it have affected any Western supplied aircraft? A p39 is hardly going to be immune to exactly the same supply problems. Indeed its hard to see why they wouldnt have had similar reliablity as the P40 which had exactly the same engine.
Ultimately we have to accept an Allison engined aircraft was superior in reliability and performance to Merlin powered airframes. And frankly thats the bit im struggling with. Its not patriotism or bloody mindedness speaking here, its just contary to everything ive read about the Hurricane in British service. I mean, it was used on carriers in the north sea, yet only seems to have a problem with the cold in Eastern Europe?