Alternative airborne guns

[Elan Vital]

main problem is the sort of lack of performance of the machine. You need a lot more power, which means bigger engines and more weight a redoing more stuff.
None of the 3 engines used were that good and a 10,000lb twin with 304sq ft of wing using roughly 700hp engines was having trouble. Once source says 242mph at sea level at normal gross weight (H-S engines?) 227mph at max gross weight. Roughly 300mph at 16,400ft but strafing seems to be a problem.
Redesigning the plane to use larger engines is possible but that takes time and money, and estimates get a lot more iffy.

Other than the versions with bigger engines, the only other path available was the GR 14S which was to the 14M what the GR 14R was to the 14N.

Then the sea level power increases from about 580 hp for each engine to 640 hp, and even 860 hp when the 14S uses the "overcharge" and 1000 hp at takeoff (14M only had a takeoff setting and no overcharge, though it can theoretically maintain that at 2900m to get 785 hp). At the rated altitude of 4000m or so, the 14M delivers 660 hp while the 14S delivers 680 hp at about 4250m, and 840 hp at overcharge.

So a direct calculation would give a sea-level speed increase of (cubic root(1280/1160)-1)*100=3.3% at sea-level and no overcharge and 14.9% with overcharge.

At the rated altitude, speed would increase by up to 8.4% using overcharge (speed would be only marginally increased if at all when the 14S is at normal power).

But the engine weight would increase by about 100 kg per engine and the engine cowling may change ever so slightly, so the increase would probably be less unless this was coupled with aerodynamic upgrades.

For a sea-level speed of about 375-390 kph, that gives new speeds of up to 387-402 kph using normal power and 425-445 kph using overcharge before arriving on the front.
At rated altitude the speed would be nearly the same when the 14S is running at normal power, and would increase from about 480 to 530 kph using overcharge.

Since the normal speed of 14S is 2700 rpm instead of 3030 rpm on the 14M, it's also possible that the 14S is more durable at normal power and would be able to maintain greater cruiser power than the 14M, so the benefit may be greater when looking at cruising speed.

Still, far from enough.

 

[Gilder]

Its an interesting point but Italy in 1926 had the Fiat AS.2 engine developed for the Schnider Race developing 800hp.

Clearly this was a one off design for racing but it would have given the Italian engineers considerable experience in how to develop a powerful engine and could be considered a missed opportunity.

 

[Shortround6]

Fiat built a lot of V 12 engines in the 1920s.
While this prolific range of engines gave a lot of experience it would not translate well into the 1930s, especially the late 30s.
The low octane fuel of the 1920s would support neither high compression or supercharging.
But since the pressures in the cylinders was low the strength of the parts (piston, con rods, crank and crankcase) could be low and thus the engine was light in weight.
They also used separate cylinders although they used one head for each bank of 6 cylinders. A 6 cylinder block is stronger for the weight but a lot harder to manufacture.
Racing engines don't have to last anywhere near as long as service engine.
The Napier Lion engine of 450-500hp in the 1920s was rated at 700hp in 1925 Schnieder cup racing and at 875-900hp in 1927. By 1929 they got 1350hp out of it with a supercharger and one of Mr. Banks exotic fuel blends.

Fiat built a few high-altitude engines using the "trick" of using high compression but not opening the throttle all the way until higher altitude was reached.
Germans were doing this in WW I with some of their engines. Pilots throttle had 3 'gates'. At low altitude the gate/slot for the handle restricted movement so that the carb/s would not fully open. At a certain altitude the handle would be handle would be pushed through an opening into the center gate/slot that allowed for more travel and at another altitude (higher) the process was repeated, and the 3rd slot would allow for full throttle. It might have also increased minimum throttle setting to keep from running too lean.
Using full throttle at 7.5 compression and poor gas could wreck the engine on take-off in the early/mid 1920s.

Steel and aluminum alloys made considerable advances in the 20s and 30s. As did valves, valve seats, valve springs.
Add casting and forging techniques all changed/advanced.