ORIGINAL: rxAxilleas
How did OS solve the problem with the oil drain at low throttle settings? (as the engines firing how it is possible to have increased suction on the nipple to drain the oil)
Axilleas,
The average pressure in the intake manifold is not dependent on the engine's firing...
When the engine fires, the manifold is separated from the combustion chamber by the closed exhaust valve.
The cylinder pressure may marginally and temporarily raise the pressure in the intake manifold, as the intake valve begins to open,
before the piston has reached TDC and also some residual exhaust pressure goes out the intake valve.
The pressure soon becomes strongly sub-atmospheric, as the piston begins to descend, sucking fresh mixture into the cylinder.
On average it is a strong partial vacuum, in all engines and in most engines, it never gets as high as atmospheric, even at full throttle.