cdrod

Can I open up the oil return holes on the ProComp aluminum heads? The lower passage in the head is much smaller than the upper section. I'd like to drill it out a little bigger but don't want to end up in a water jacket - that would be a bad day! Here's a pic.



Can I drill this bigger to help get the oil back to the pan faster?

olds 307 and 403

You can if you want but I don't see the point. On a 455, yes. A 350 stroker with a 7 qt pan, why?

Ozzie

I'm not familiar with those heads, so perhaps my comments should be disregarded. I would think that if the drains will be able to keep up with the oil flow it will be O.K. as is. Some stock heads with congested drains due to crud have made problems. Your photo appears to show some sort of a bushing in the hole. ??? I'm wondering how the drains compare to the factory heads. You might consider contacting the manufacturer with your concerns. If you can't "feel" where the wall is through a coolant passage proceed very carefully.

cdrod

Hey guys, thanks for all the advice. I compared the ProComp head to a set of '72 stock 7a heads I have in the garage. The drains are very similar in size, so I decided against any modifications. It will be a daily driver and shouldn't spend much time above 4500 rpm.

Rodney

joe_padavano

Personally, I am of the opinion that anything you can do to facilitate the flow of oil back into the pan is a good thing. Smoothing and slightly enlarging oil drainback holes can't hurt. At a minimum, allowing the oil to drain out of the heads faster will reduce the possibility of valve cover leaks.

lemoldsnut

I agree with Joe. I also have noticed that some head gaskets don't line up well and could use some trimming to do a better job. Check that too. Then the typical grinding here and there to get the block cleaned up to flow better is good as well.

Just my two cents

Larry

wr1970

I agree with Joe P. and lemoldsnut. You could smooth slightly and round out passage a little by beveling it. Also your pencil is pointing at lower side of head and the upper passage is the top. How big is the return in the block in relation to the head lowerside ?Got and measurement pics?Would like to see picture the head top passage way on the oil return as well.Nice picture you posted!

cdrod

wr1970:
Here is a pic of the upper side of the oil return hole in the ProComp heads. It's about 5/8" in diameter and 1" deep pretty much perpendicular to the deck (45˚ angle). The bottom of this passage meets with the smaller hole from my previous pic which travels almost horizontal and exits into the lifter valley of the block. The hole in the head gasket is larger than this smaller passage so its not a restricting the flow of oil to the lifter valley. I'm afraid I'll hit water if I drill out the smaller passage, so looking to see if others have good experience drilling the lower passage.



Upper drain back hole in the top of the head.