Among the innovative and/or unusual design features of Itala’s Grand Prix car, perhaps the most radical was the method of induction of the charge into the cylinders. Here are two contemporary descriptions:
The Autocar, 25-6-26
…Another interesting feature of this engine is the method of supercharging and of scavenging the cylinders. On the rear of the mainshaft is a Roots blower, driven through a flexible coupling, which draws air through a filter, and is in tandem with the Bosch electric lighting generator. The blower, however, is independent of the carburettors, and is made use of merely to supply compressed air to the cylinders, through ports at the bottom of the cylinder barrels, uncovered by the pistons at the end of the stroke. Compressed air entering at the end of the firing stroke scavenges the cylinder, and, at the end of the induction stroke, air is admitted to dilute the mixture to the correct degree.
Automotive Industries, 15-7-26
....Another unusual feature of the engine is the supercharger arrangement. Driven off the rear of the crankshaft, through a flexible coupling, is a Roots blower which takes its air through an American cleaner. Instead of being connected up with the carburettors, the blower supplies compressed air to the cylinders through ports uncovered when the piston is nearing the bottom of its stroke. The air driven into the cylinders at the end of the firing stroke forces the spent gases through the exhaust valves, while the air admitted at the end of the intake stroke dilutes the very rich charge supplied by the carburettors and changes it into an explosive mixture.
Comment:
Scavenge ports near the bottom of the liner are standard practice in the modern low-speed, two-stroke marine diesel, though in this case exhaust valve(s) only is/are provided at the cylinder head, thus giving “Uniflow” scavenging (as opposed to earlier schemes of cross-flow or loop scavenging). Such ports on a four-stroke engine, which is also provided with normal valves in the cylinder head, are surely unique.
But this also means certain difficulties. When the piston is in the upper part of its stroke, preventing the supercharge air from entering the crankcase is problematic, unless the piston is inordinately long, and equipped with one or two rings low down on the skirt; naturally the liner must also then extend a long way down, which in turn, necessitates a very long connecting rod. Which of course means a tall and heavy engine.
Also, since the supercharger delivers air to the cylinder twice in every cycle, it could consume more power than the usual, in which only one delivery per cycle is provided. This is not insignificant: power consumption of the mechanically driven supercharger is known to be of the same order as the net power output of the supercharged engine, hence there might not be a net benefit in this case.
There would also appear to be difficulty in charge preparation: thorough dispersal and evaporation of the fuel droplets, which would naturally be larger and more plentiful in the very rich mixture, as would be drawn through the carburettor. And with very little time, within the cylinder, to achieve this. That’s in addition to low volumetric efficiency, because the inlet valve open period would necessarily have to be restricted, to allow for the scavenge port open period. The unusual valve arrangement, with their axes at right angles to the cylinder axis, could not have helped in this respect, either.
Much of this speculation could be resolved by a cross-sectional drawing of the engine, and some more by a port/valve-timing diagram: does anyone have one which can be reproduced here without breach of copyright? Or even a description that provides more detail than those I have quoted above? Incidentally, the content and sequence of both these, betrays their origin: surely from a press release by the company.
