Yeah, that's my thought, too. Even if we allow a generous 25hp.Hardly seems worth the effort to retool and deal with the logistics of tracking different cams, etc. for a 1-2% gain.
That's an interesting idea. I had no idea roller followers were even around yet.The Allison might have been improved by the much faster valve action of a race type roller cam follower setup. In aviation, roller cam followers were used in most radial engines (because of high cam surface velocity rather than to permit rapid actuation.
Just for giggles - what if Allison looked at their maturing 1937 engine, looked at developments in Germany and at their round-engine competitors, and somehow (rohypnol?) persuaded the Air Corps that continuing development but in V-2150 form would be Just The Thing to ensure a technical lead?1931 was the Allison's first run and 1937 was the first time an Allison engine lasted 150 hours and the Allsion only went into full production in 1939/1940.
The Merlin for comparison was first run in 1933 and passed a 150 hour test in 1935, went into full scale production in 1936.
Just for giggles - what if Allison looked at their maturing 1937 engine, looked at developments in Germany and at their round-engine competitors, and somehow (rohypnol?) persuaded the Air Corps that continuing development but in V-2150 form would be Just The Thing to ensure a technical lead?
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The approach I would have taken if with one of the engine companies in, say 1934, would have been to lay out a narrow angle V-8, with bore and stroke perhaps 10% larger than Allison or Rolls. This would go from a nominal 5.6" bore and stroke (1655 cubic inches for 12) to a 6.25" cylinder for a 1534 cube light weight V-8, 2300 cube V12 or, with two V-8s a contraprop ready V-16 of 3070 cubes, patterned loosely on the Ford V-1650 and Chrysler IV-2220. Aluminum crankcase and blocks cast as a whole, blowers on the sides- possibly underneath as well. Two big valves per cylinder, in line with single overhead cam and roller lifters. Constant flow port injection. Wet liners. Two rods per crank throw. And hire Leo Goosens for the layout drawings! Guarantee 1.2 HP/cubic inch on grade 100/115 fuel and see what happens.
Dynasoar
The approach I would have taken if with one of the engine companies in, say 1934, would have been to lay out a narrow angle V-8, with bore and stroke perhaps 10% larger than Allison or Rolls. This would go from a nominal 5.6" bore and stroke (1655 cubic inches for 12) to a 6.25" cylinder for a 1534 cube light weight V-8, 2300 cube V12 or, with two V-8s a contraprop ready V-16 of 3070 cubes, patterned loosely on the Ford V-1650 and Chrysler IV-2220. Aluminum crankcase and blocks cast as a whole, blowers on the sides- possibly underneath as well. Two big valves per cylinder, in line with single overhead cam and roller lifters. Constant flow port injection. Wet liners. Two rods per crank throw. And hire Leo Goosens for the layout drawings! Guarantee 1.2 HP/cubic inch on grade 100/115 fuel and see what happens.Dynasoar
I wonder if it's occurred to them, yet, to want a burn that's as spherical as possible, & so dished pistons, rather than domed. (Heart-shaped combustion chambers, to induce swirl, seem extraordinarily unlikely.)Understanding of combustion chamber design was progressing rapidly in the late thirties, both in aviation and automotive engines. In the absence of computer technology such approaches as casting top dead center volume in plaster, then spherically milling material away at constant radius from the sparkplug to create models of non-turbulent combustion propagation, then correcting for mixture turbulence (visualized by other equally primitive means), and guessing at the effects of surface quenching, resulted in knock-free combustion at increasing compression ratios. Combustion chamber evolution was not needed in aviation engines beyond WW2, but progressed very effectively for automobiles in the late forties/early 50s.
The technology for the creation of smooth combustion in larger aircraft engine cylinders was there for the taking in the thirties but no one (with the possible exception of Sir Harry Riccardo) did much analysis.
I know the Germans tended toward larger, more lightly built, lower BMEP engines, and the American emphasis, for some time, was concentrated on small cylinders operating at high BMEP.
The approach I would have taken if with one of the engine companies in, say 1934, would have been to lay out a narrow angle V-8, with bore and stroke perhaps 10% larger than Allison or Rolls. This would go from a nominal 5.6" bore and stroke (1655 cubic inches for 12) to a 6.25" cylinder for a 1534 cube light weight V-8, 2300 cube V12 or, with two V-8s a contraprop ready V-16 of 3070 cubes, patterned loosely on the Ford V-1650 and Chrysler IV-2220. Aluminum crankcase and blocks cast as a whole, blowers on the sides- possibly underneath as well. Two big valves per cylinder, in line with single overhead cam and roller lifters. Constant flow port injection. Wet liners. Two rods per crank throw. And hire Leo Goosens for the layout drawings! Guarantee 1.2 HP/cubic inch on grade 100/115 fuel and see what happens.
The advantage of a V12 over a V8 for A/C use is that it is a natually balanced engine design with very little vibration. V8's can be made smooth (90* bank angle, cross plane crank, and/or harmonic balancers, etc.) but that all adds complexity and rotational weight. For smooth power delivery it is hard to beat a V12.You might be right about big V8 rather than V12, for less parasitic loss.
With OHV/OHC (1/bank), IMO you've got about as simple a valvetrain as you're going to get. About the only gain I see there is in changing from a 30deg valve seat angle to 22deg, & I expect that's beyond the known tech.phx and EverKing,The intent of using two larger valves rather than four smaller was, primarily to provide piston top area for a relatively large quench/squish region to promote strong turbulence while increasing detonation margin. The reduction of valve area and perimeter would not be a 2 to 1 loss by any means and the combustion chamber shape is intended to permit operation at relatively high boost and increase intake flow.
Simple valve gear would lighten things, tho the cylinder offset from bank to bank to permit simplified rods might introduce some shake.
I would agree completely; I only meant, if we accept the V8 is preferable, it has the advantage of lower parasitic losses.For smooth power delivery it is hard to beat a V12.
I think for 1940's tech a V12 is still the way to go.