oil pumps and internal by-pass

[L89 chevelle]

Why do oil pumps by-pass oil back into the pick up and not into the oil pan. I am thinking of pluging the internal by-pass and venting back into the pan with the same size orfice. I would think this would be better and less chance for scatter or cavitaton.

Thoughts?

[old blue 75]

DV has info on that exact thing in one of his sbc books. You can buy a pump
already set up like that. They are from System One.

[L89 chevelle]

Originally Posted by old blue 75

DV has info on that exact thing in one of his sbc books. You can buy a pump
already set up like that. They are from System One.

Do you know what book that was?
The one from System One looks like the one I just built. Mine don't have the screen. I just moved the by-pass ahead and made a new one venting to the pan. Had to shim the psi spring now mine starts by-passing at 50lbs and is full by-pass at 55lbs. max psi is 60 to 65 with a drill wot spinning solvent.

Any thoughts DV

[old blue 75]

IIRC the screen is to stop the oil from shooting into the sump and bouncing
back into the spinning crank. I think it is in the budget sbc book.

[Lasse]

Originally Posted by L89 chevelle

Why do oil pumps by-pass oil back into the pick up and not into the oil pan. I am thinking of pluging the internal by-pass and venting back into the pan with the same size orfice. I would think this would be better and less chance for scatter or cavitaton.

Thoughts?

In that case you have to make bigger tube for pickup. Otherwise there is risk for pump cavitation. Take a look at Vizard's book Chevy Small Blocks On A Budget.

[L89 chevelle]

Originally Posted by Lasse

In that case you have to make bigger tube for pickup. Otherwise there is risk for pump cavitation. Take a look at Vizard's book Chevy Small Blocks On A Budget.

??? what bigger then a 3/4in?
Thats why we are by-passing outside rather then in the pick up tube to prevent cavitation.

[Lasse]

Originally Posted by L89 chevelle

??? what bigger then a 3/4in?
Thats why we are by-passing outside rather then in the pick up tube to prevent cavitation.

If you by-pass outside inlet of pump, so pump must get all the oil trought pick tube vs. by-pass is recirculating oil to inlet. That's why tube comes more restrictive. I recommend reading oil pumps chapter from Vizard's book, it is very good text.

[L89 chevelle]

Originally Posted by Lasse

If you by-pass outside inlet of pump, so pump must get all the oil trought pick tube vs. by-pass is recirculating oil to inlet. That's why tube comes more restrictive. I recommend reading oil pumps chapter from Vizard's book, it is very good text.

A 3/4" tube can't be more restrictive then a -12 or -16 pick-up on a drysump. no?

[Lasse]

Originally Posted by L89 chevelle

A 3/4" tube can't be more restrictive then a -12 or -16 pick-up on a drysump. no?

This is from Vizard's book:

"By externally bypassing oil, a problem can be created on the induction side of the pump as the demand through the pick-up pipe is increased greatly. This can cause the pump to cavitate and momentarily starve the bearings. To combat this, the stock half-inch pickup, which at best is marginal, needs to be enlarged to about 5/8-inch diameter"

So yours must be adequate, any way is it OD or ID. Sorry I didn't remember what was stock size of pick-up tube.

[L89 chevelle]

Originally Posted by Lasse

This is from Vizard's book:

"By externally bypassing oil, a problem can be created on the induction side of the pump as the demand through the pick-up pipe is increased greatly. This can cause the pump to cavitate and momentarily starve the bearings. To combat this, the stock half-inch pickup, which at best is marginal, needs to be enlarged to about 5/8-inch diameter"

So yours must be adequate, any way is it OD or ID. Sorry I didn't remember what was stock size of pick-up tube.

5/8 is stock, 3/4 is a std upgrade.