Thought i better post this one in the holden section. I'm not sure on the oiling paths for other marques.
After deburring the block, I looked at other ways of getting the oil from the heads to the sump. The next obvious place to look was the heads.
Holden V8s have a history of oil leaks from rocker cover gaskets due to too much oil in the heads when a high volume oil pump is used, so we'll explore why it is so. (apparantly not due to the glass and a half of milk).
The heads have only 4 X 10mm holes to drain oil from the heads back to the sump via the valley. These holes sit almost horizontal when the heads are on the motor, so gravity is not your friend.
and here's a picture
I drilled the holes out to 7/16", which is just over 11mm, because it's what I had. It still leaves over 2mm of metal between the oil return hole and the water galleries.
Now, enlarging a 10mm hole to approx 11mm doeasn't sound like much, but it gives an increase in area of 21%. The 7/16" bit i used gives an increase of 23.4%.
I'd be greatly appreciative if somebody has the flow rates for standard and high volume pumps
And here's a picture of the drilled gallery
A pic of the top of the heads showing the difference. The unmodified head is on the left.
Pic from the bottom with the unmodified head again on the left.
The holes have to be drilled from the bottom of the heads.
VERY CAREFULLY. I put half a dozen layers of thick, silver tape over the hole and drilled through that. Slowly, slowly, wins the race. Even taking your time, it only takes about 2 minutes per hole.
Clean up with a die grinder and chamfer the holes and you're away
All that's need now is a quick shave to clean up any dags and ensure the surface is flat and then it's time to put it all back together.