Italy usually get little attention in the alternate history discussion, but i want to put forward a little pet peeve of mine regarding italian engines and indirectly aircraft.
Some folks are keen to advocate german-japanese engine cooperation in WW2, arguing that japanese radials were so much better etc. I'm not particuarly keen on that, the germans had some excellent engines and the fact that they haven't fared better is mostly self-inflicted (cancelling the DB-603 or the Jumo-222 saga for instance), besides the japanese engine usually looked at, Homare and MK9, were far too late to be of any interest/help to Germany, even if on paper they seem considerably better than BMW-801 (debatable imo).
However, compared to Italy's radials, the japanese radials of the same era were really generations ahead, the japanese build tens of thousands of two-speed engines, and thousands of 1500HP engines, not to mention thousands of 1800-2000HP engines, although mostly unreliable due to the war situation.
Italy on the other hand, despite having some really promising engines actually conceptually ahead of the japanese, namely their big 18 cylinder radials, the AR-135, Piaggio PXII and Fiat A80 series, failed to build any meaningful numbers of either 2 speed engines or 1500HP ones. Really the only way they tried to increase power was by just blindly increasing displacement (which mortally unbalanced the engine) rather than rpm and supercharger improvements, but they were never successful. The only engine that barely approached the contemporary prewar japanese engines as far as HP/liter ratio, rpm etc is the 31,4 liter A74, it really is in the class of the 28 liter Sakae/Zuisei in power (840-870HP vs 900-950HP) but it's almost same size as the 32,7 liter 1000-1070HP Kinsei, which imo was the best Axis radial pre-war.
So rather than german-japanese cooperation on radials, how about ITALIAN-japanese cooperation on radials? I'll give some examples of what i have in mind if the italian engines were somehow crossbred with the japanese engines.
The Fiat A74 was almost as big as Kinsei but was never developed as succesfully. So image it crossbred with Kinsei-40, it can already be uprated to 950-975HP in 1939, and a two speed model equivalent to the 1300HP Kinsei-50 can give say 1200HP in 1942. If Italy stays in the war longer it can give 1400HP with water-methanol boost in 1944! This without increasing displacement or diameter at all.
Let's take the Piaggio PXI of 1000HP and 38,7 liter, the closest japanese equivalent being the 37,5 liter Ha-5. At first they were more or less equivalent, but then the japanese got the 1250HP Ha-41 in 1941 and the 1450 HP Ha-109 in 1942. The italians barely managed to get it to 1175HP in 1942 in the PXIX version. But a crossbred PXIX should easily do 1250HP in 1941, and a two-speed model 1450HP in 1942. Surely the Reggiane fighters will be greatly improved having that much more power, and i haven't even got into a potential later-war 1700HP water-methanol boosted variant, assuming Italy is still in the war by then.
We get now into the italian large 18 cyl engine which at first had no japanese equivalent.
The 1000 HP A80 was a 45 liter beast but running at a ridiculously low rpm, nearest japanese equivalent is the 1500HP 42 liter Kasei. A crossbred A80 then can easily do 1250 HP prewar, and 1500HP without breaking a sweat when fitted with a 2 speed supercharger, say about 1941-1942.
The Alfa Romeo 135 was a 49 liter 1500HP engine, but "nipponized" could easily do 1800 HP.
The Piaggio PXII of 53 liter and 1500 HP (really R-3350 or Ha-104 size), which also can do 1800-1900HP without effort.
Though one of the above should be dropped as there's too much size overlap, perhaps just keep the A80 and PXII famillies.
Finally, the completely wasteful and useless Isotta Fraschini air cooled inlines like the 26 liter Delta could be replaced by an italian equivalent of Zuisei or R-1535, then the initial 750-800HP rating could be increased to 950-1000 with a two-speed supercharger, a more reliable and dependable engine than the Delta ever was.
What the japanese could use from the italians is the idea of getting into big 18 cyl radials earlier, i was speaking about the 44 liter 1800HP Mamoru elsewhere, so instead of it how about an 18 cyl 48 liter early Ha-219 (it used Ha-5 family cylinders) also of 1800 HP, but of less diameter, less strain on the engine and excellent development potential.
I haven't touched the italian inlines, really they're just better off building as many DB-601/605 as they can in that respect. Maybe they could do something with the Asso but with DB around it will just be wasteful. If in this timeline the germans don't cancel the DB-603, build that one too (in OTL they did planned to build the DB-603 under licence, but never got that far)
So then the nipponized A74, A80, PXI and PXII families plus a small 26-27 liter Isotta Fraschini 14 cyl radial, in addition to DB inlines, should cover all the needs and give a huge boost to all the italian aircraft equipped with them.
Some folks are keen to advocate german-japanese engine cooperation in WW2, arguing that japanese radials were so much better etc. I'm not particuarly keen on that, the germans had some excellent engines and the fact that they haven't fared better is mostly self-inflicted (cancelling the DB-603 or the Jumo-222 saga for instance), besides the japanese engine usually looked at, Homare and MK9, were far too late to be of any interest/help to Germany, even if on paper they seem considerably better than BMW-801 (debatable imo).
However, compared to Italy's radials, the japanese radials of the same era were really generations ahead, the japanese build tens of thousands of two-speed engines, and thousands of 1500HP engines, not to mention thousands of 1800-2000HP engines, although mostly unreliable due to the war situation.
Italy on the other hand, despite having some really promising engines actually conceptually ahead of the japanese, namely their big 18 cylinder radials, the AR-135, Piaggio PXII and Fiat A80 series, failed to build any meaningful numbers of either 2 speed engines or 1500HP ones. Really the only way they tried to increase power was by just blindly increasing displacement (which mortally unbalanced the engine) rather than rpm and supercharger improvements, but they were never successful. The only engine that barely approached the contemporary prewar japanese engines as far as HP/liter ratio, rpm etc is the 31,4 liter A74, it really is in the class of the 28 liter Sakae/Zuisei in power (840-870HP vs 900-950HP) but it's almost same size as the 32,7 liter 1000-1070HP Kinsei, which imo was the best Axis radial pre-war.
So rather than german-japanese cooperation on radials, how about ITALIAN-japanese cooperation on radials? I'll give some examples of what i have in mind if the italian engines were somehow crossbred with the japanese engines.
The Fiat A74 was almost as big as Kinsei but was never developed as succesfully. So image it crossbred with Kinsei-40, it can already be uprated to 950-975HP in 1939, and a two speed model equivalent to the 1300HP Kinsei-50 can give say 1200HP in 1942. If Italy stays in the war longer it can give 1400HP with water-methanol boost in 1944! This without increasing displacement or diameter at all.
Let's take the Piaggio PXI of 1000HP and 38,7 liter, the closest japanese equivalent being the 37,5 liter Ha-5. At first they were more or less equivalent, but then the japanese got the 1250HP Ha-41 in 1941 and the 1450 HP Ha-109 in 1942. The italians barely managed to get it to 1175HP in 1942 in the PXIX version. But a crossbred PXIX should easily do 1250HP in 1941, and a two-speed model 1450HP in 1942. Surely the Reggiane fighters will be greatly improved having that much more power, and i haven't even got into a potential later-war 1700HP water-methanol boosted variant, assuming Italy is still in the war by then.
We get now into the italian large 18 cyl engine which at first had no japanese equivalent.
The 1000 HP A80 was a 45 liter beast but running at a ridiculously low rpm, nearest japanese equivalent is the 1500HP 42 liter Kasei. A crossbred A80 then can easily do 1250 HP prewar, and 1500HP without breaking a sweat when fitted with a 2 speed supercharger, say about 1941-1942.
The Alfa Romeo 135 was a 49 liter 1500HP engine, but "nipponized" could easily do 1800 HP.
The Piaggio PXII of 53 liter and 1500 HP (really R-3350 or Ha-104 size), which also can do 1800-1900HP without effort.
Though one of the above should be dropped as there's too much size overlap, perhaps just keep the A80 and PXII famillies.
Finally, the completely wasteful and useless Isotta Fraschini air cooled inlines like the 26 liter Delta could be replaced by an italian equivalent of Zuisei or R-1535, then the initial 750-800HP rating could be increased to 950-1000 with a two-speed supercharger, a more reliable and dependable engine than the Delta ever was.
What the japanese could use from the italians is the idea of getting into big 18 cyl radials earlier, i was speaking about the 44 liter 1800HP Mamoru elsewhere, so instead of it how about an 18 cyl 48 liter early Ha-219 (it used Ha-5 family cylinders) also of 1800 HP, but of less diameter, less strain on the engine and excellent development potential.
I haven't touched the italian inlines, really they're just better off building as many DB-601/605 as they can in that respect. Maybe they could do something with the Asso but with DB around it will just be wasteful. If in this timeline the germans don't cancel the DB-603, build that one too (in OTL they did planned to build the DB-603 under licence, but never got that far)
So then the nipponized A74, A80, PXI and PXII families plus a small 26-27 liter Isotta Fraschini 14 cyl radial, in addition to DB inlines, should cover all the needs and give a huge boost to all the italian aircraft equipped with them.
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