Found a spare P6B air cleaner to play with locally. More thoughts on the shape of the inlet 'cone' - Bernoulli's work says that when a fluid emerges from a pipe into a large space volume and its speed drops, the pressure goes up - makes me wonder about changing the shape of our inlet. Will the effect be significant? Only at high power output? The Penguin tests using an air cleaner with an enlarged inlet showed a useful increase in peak power, but I didnt register what happened lower down the curve.
The Hawker sea fury, with a large radial of some 3000hp, has a very large spinner, leaving what appears to be an annular gap of only a few inches to the cowling. This fits with Bernoulli, as there is a large space around the front casing of the engine in which the air slows and pressure increases before hitting the cylinders.