Don Terrill’s Speed-Talk

As the title states, I am looking for help with calculating motor oil flow through an orifice. In this case the orifice is a standard carburetor jet. The purpose is to determine the flow capacity requirement of a small gear pump to lubricate a turbocharger in a closed loop system. General guidelines for a sleeve bearing style turbocharger is an .065" restrictor at the oil inlet at normal engine oil pressures. I can find orifice calculators online and the specific gravity of a synthetic oil of .85 but there isn't an input for viscosity. The result is roughly .42 gpm. using a pressure drop of 50 psi. I do realize the idea may be totally impractical but right now this is just theory for an approximate temperature range of 0*C to 100*C.

You'd need to know what the 2nd orifice size is in order to calculate it, the turbo brg system itself is the 2nd orifice, also the pressure drop due to line length/fittings. Best bet is to just put a pressure gauge on it shoot for 40 PSIg at the turbo inlet at temp and full load for a journal brg std thrust brg system. Around 10cc/sec flow rate. Halve that for ball brg.

For midframe sized turbos an orifice size of .040"-.050" will have about a 50% pressure drop from supply pressure on 20w-50 at operating temp of near 100c.

The reply is much appreciated. I realize the actual flow rate would be lower than just the orifice due to bearing clearance but without actually having a complete assembly to test, I was looking at the maximum possible flow rate to search for an appropriate pump. If my math is good, 10/cc per second is about 0.16 gpm? I will try a bench test of orifice/bearing setup per your suggestions although I don't know of the validity due to the lack of shaft rpm.

Set the engine to a fast idle and catch the oil coming from the turbo drain line . . . after the oil is warm of course.

-jim

If the system was together, I would do just that. This is for a possible rear mount setup using a brand new, but very old Garrett turbocharger. This will be for a self-contained oiling system, not the typical engine oil plus scavenge pump.

If its electric pump you should be able to preheat the oil and static test it. Does it have both a scavenge pump and a pressure pump? Oil coming out of the turbo will be heavily aerated, single stage setup is not ideal, need a gravity fed sump under the turbo with a vent and oil/air separation baffles.

I don't have a pump yet, that was the primary reason for the initial post. I do have a small 12v hydraulic pump that may be usable, although the motor isn't designed for continuous duty, but would probably be okay for a test per suggestion. The intention is to be pressure pump only with a combination reservoir/sump for the turbo drain. There will be a cooler in the pressure feed, possibly fan cooled. Maybe all a pipe dream but I already have all of the parts required except the pump itself. The suggestions are all appreciated.

Most turbo manufacturers will recommend a pressure for the oil supply. If you buy a pump with an adjustable pressure regulator you should be set. Regulating pressure is better than an orfice, as there is less possibility for the supply line to get blocked by debris.

-jim

4sfed wrote:Most turbo manufacturers will recommend a pressure for the oil supply. If you buy a pump with an adjustable pressure regulator you should be set. Regulating pressure is better than an orfice, as there is less possibility for the supply line to get blocked by debris.

-jim

DOH! Could you make that sound more complicated so I don't feel like I missed the obvious

A regulator IS an orifice, it just ain't fixed.

Grocerius Maximus wrote:A regulator IS an orifice, it just ain't fixed.

10-4 on that.

This calculator should get you close:

http://www.efunda.com/formulae/fluids/c ... wmeter.cfm