odonnell

This is a bit of a weird post - I'm doing a project for a fluid mechanics class I'm taking, and decided to plot a 3D surface of oil flow rate through a 944 main oil gallery (as a function of engine RPM as well as oil temperature). If you think that's super nerdy, you're right. I just wanted to choose a topic that I actually cared about.

For the project, I want to model the 944 oil pump geometrically, so I can give a rough estimate of how much oil it moves (volumetrically) per revolution of the crank. Anyone have the dimensions handy?

After that, I'll be using PDE's and Navier-Stokes equations to calculate the theoretical pressure post-pump pressure. I will plot this RPM-versus-pressure curve across different temperatures, because I can get temp vs. viscosity data online.

So basically, it's not for a practical purpose - it's just for a research project and I'm looking for any pointers as far as modeling the pump-to-gallery control volume. All dimensions and insight are welcomed - I'm still learning

Perhaps the most helpful (by far) would be some numbers for your oil pressure at given RPMs, at operating temp. I understand that varies depending your oil, and things like bearing wear. I'll end up averaging them out anyway. I'm looking for "X pressure at Y rpm" for 1000 RPM, 1500 RPM, etc... to 4500 RPM or so. The interior oil pressure gauge will have to do - don't want to overcomplicate things.

I apologize if this is too off topic...

V2Rocket

with warm oil, 20W50 conventional, in ~85* weather, my oil pressure is 3.5 bar at idle (1000rpm), 4 bar by 2000 rpm and 5 bar+ (max on gauge) by 3000.

50,000 miles or so on totally rebuilt engine, 85.5 style engine factory installed in 85.0 car. maybe someone could lend you a spare oil pump.

Dougs951S

Michael, wish I had a spare pump on had to give you an internal volume, that's what you really need since it is a positive displacement type device. Running synthetic 20w50 I see 3 bar at hot 1000 rpm idle, 4 bar by 1900ish rpm and 5 bar by 2600ish. You know the condition of my motor.

Hope that helps, sounds interesting but thats probably because I'm as much of a nerd as you are. Worth noting that on cold starts when the OPRV is bypassing much of the flow, the pump is putting out roughly 5.5 bar and above 2k rpm when cold that pressure can reach 7 bar.

Van

Pressure and flow are very different. Think of two hoses, one that's a small diameter, like a garden hose, and one that's a large diameter, like a fire hose - you can have 5 bar (~65psi) in each one, but the flow out of the fire hose will be a lot more than the flow out of the garden hose.

Also be aware that there are early and late oil pumps - the later pumps have a thicker gear set (meaning the volume of each tooth spacing is larger) and pump more volume.

Now, for pressure, and trying to average together people's pressure reading, remember that we all have an OPRV (oil pressure relief valve) that's spring loaded so the system doesn't go higher than 5 bar.

What you need is a good picture or measurements of the gears inside an oil pump, so you can calculate the volumetric space of each tooth. Then, you can figure out the number of teeth that move per revolution, and then you'll have your flow rate for RPM (which will be linear).

How much bleeds past the OPRV? I don't know. But, if I had to guess, I say 25%-50% of the flow when the pressure gauge says 5 bar. (Meaning, if the engine is hot, and at 2k RPM it shows 4 bar on the gauge, nothing is going past the OPRV, but at 4k RPM, if the gauge is 5 bar, then *something* is going past the OPRV.)

odonnell

Thanks for the info guys!

I decided that since the point of the problem is to solve an unknown, I might solve the pump flow rate as a function of RPM and oil temp, assuming 20w50 properties. I'll use the assumption that sender reads the static post-pump pressure, and given some gallery dimensions and minor loss coefficients for bend and valves, be able to give an approximate relationship. Then, I can compare that to geometically calculated pump flow.