Rick360 wrote:That sounds way more complicated than it needs to be. Keep it simple.
I also don't like putting the relief far away from the vacuum pump line. Any relief air that comes in flows thru the engine that way - not good and carries more oil with it. Open the drain holes big enough in the block and heads and if your rings seal good you wont have enough air flow out of the engine to be a problem.
At high rpms, oil with air entrained in a moving engine rather than on a non-tilt dyno, is like soda water when it emerges from the bearings. Foam does not flow so easily as neat oil. I think there are many examples of "oil filling the heads" which are explained easily with increased bulk due to decreased density which are attributed to the drain holes not being big enough*. Drawing air down through the drain holes via the crankcase encourages the evacuation of the heads. Just like the suction water basins on airplanes.
The flow of oil to the heads is essentially a constant past a certain rpm. It will drain under gravity or with an assist. Put the vent on the left bank as you look at the crank pulley. This will actively work to combat oil being driven up the drain ports which is useful.
* Keep in mind that OEM testing includes hundreds if not thousands of hours cycling back and forth between peak torque and hp on a dyno. If the drains were not properly sized this problem would show up quickly. Oil pump flow only increases very gradually after the pressure relief is hit. Of course, if you have done something to deliberately increase flow to the heads that is another story. Often it is just the opposite in racing engines.
In addition, the head which has no venting will have more stress on the intake and exhaust valves/guides. Exhaust pressure will try to flow out and expel oil and fouled gas from the guide and being in local proximity/communication to/with the intake valve guide this will encourage more oil being taken in and burned in the engine but with unfiltered atmosphere to boot. For the changed local conditions to communicate with the vacuum-pump-with-close-proximity-relief-valve requires transit through the crankcase. So in trying to make something simpler the complexity of the system increases. By providing a properly sized relief valve, it should preferentially provide additional atmosphere to the interior of the valve cover and reduce the proclivity of the exhaust valves to provide same. This is all assuming excellent ring seal. There is no doubt that there are less expensive ways to do things but overall simplicity is not so straight forward to achieve as one might suspect.