Oil drainback question

[jacksoni]

I am adapting a DOHC head to a 4 cyl GM block. Oil supply will be through an external feed line to the oil gallery in the head, diameter 15/64 to feed the cams and lobe oiling needs. Stock drainback on this head is through 5 approx 3/8 drain holes down through the original block to the pan on the down hill side and with a couple of breathers on the uphill side (originally a V8 head). I had planned to run external lines from the original drain holes to the pan or old lifter gallery (need some oil supply there for thrust bearings). It occurs to me that 1) there is no venting in this plan to the cam/valve gallery and 2) if there is any positive crankcase pressure- it is a dry sump engine so should produce some pan vacuum at speed but maybe not at low rpm's- that there will be no drainage from the cam gallery- it might be blowing the other way. My dry sump pump is 3 stage only with both suction stages plumbed to the pan. Should I run some sort of vent from the pan to the cam/valve area? Plumb additional suction lines to the dry sump pump ( I know putting a "Y" in the suction lines is basically a no-no) but maybe would work in this setting? Thoughts? Suggestions?

Thanks

[pamotorman]

make sure the drain back holes are not on the upward windage side of the crankcase. the wind generated by the crankshaft can prevent the oil from returning to the sump because the windage is trying to blow up the drain back holes . we had this problem when racing the vega engines

[jacksoni]

make sure the drain back holes are not on the upward windage side of the crankcase. the wind generated by the crankshaft can prevent the oil from returning to the sump because the windage is trying to blow up the drain back holes . we had this problem when racing the vega engines

I do have a crank scraper that may help that scenario but is a good point. Thanks.

[Kevin Johnson]

Add a standpipe to one or two of the drains wherever you want gases to communicate between volumes.

[BlitzA64]

I had drainage issues with my 4cyl do to exactly what you are saying. I bought a pump with an extra suction stage, it is a smaller stage and I used it to suck the head. You could just seal the engine (no vents at all) but I am not sure the 2 suction stages would be enough for vacuum all the time.

[jacksoni]

I had drainage issues with my 4cyl do to exactly what you are saying. I bought a pump with an extra suction stage, it is a smaller stage and I used it to suck the head. You could just seal the engine (no vents at all) but I am not sure the 2 suction stages would be enough for vacuum all the time.

Thanks, Blitz and Kevin. I think this is what I will do, add a stage to my dry sump to suck the head and some sort of balance pipe to be sure the head and pan are similar. Seal the engine.