[djustice]

I got the chance to borrow a garage with a pit for a day. so i did some testing. started car fully warmed up til fans kick on .

At idle there is no leak at all . i got a person to stay in the car and press the throttle, after about 30 seconds at about 2-3000 rpm i could see a tiny amount comming from the lip on the hump running back towards the centre rubber nub and collecting around that nub, but very slowly.

I removed the pan all pan bolts. and found that i had used silicone against the rear main camp, but no silicone between gasket and oilpan hump, so i brake kleened the hump on the pan about 4-5 times and i also got a q-tip with brake kleen barley op to scrub the gasket for oil.
Used a liberal amout of RTV ultra black let it set up for a little while then loosley tigthend the oilpan bolts, let is sit for just under 1 hour.

Repeted the same test again with no leak. for good mesure i backed the car out and took it for very short but spirited drive up to about 5000 rpm (1.st gear since i was drivng to densly populated area. Back on the inspection pit i found it had started leaking.

From this i can only assume i am not pulling a vacuum in the crank case with my current pcv system. I am heading up the later today with a vacuum gauge (messures both vaccum and pressure) so wil do some testing with a fixed orifice valve i made myself with a 0.100" opening and a standard motor PCV Valve V112 . After doing some reading on this forum it seems the old stock valve for a pontiac 455 i guess flowed about 4.5 cfm.

To find out what orifice size is needed at any given vacuum i found an intresting chart at an aircompressor site:

Vacuum Flow Through Orifices
Figures in body of chart are in air flows in SCFM (Standard cubic feet / minute)

Orifice Diameter (In)” Vacuum in inches of mercury
2″ 4″ 6″ 8″ 10″ 12″ 14″ 18" 24″
1/64″ .018 .026.032 .037.041 .045 .048 .055 .063
1/32″ .074.100 .128 .148 .165 .180 .195 .220. 250
1/16″ .300. 420. 517 .595 .660 .725 .780.8801.00
1/8″ 1.20 1.68 2.06 2.37 2.64 2.89 3.12 3.53 4.04
1/4″ 4.78 6.74 8.25 9.52 10.6 11.6 12.4 14.0 16.2

Source: https://trident.on.ca/engineering-in...orifice-table/