Engine vs Filter Restriction Ratio

[SuperBusa]

What would you say the typical oil flow restriction ratio is between engine & filter?

I’m coming up with 15:1 – meaning the engine is 15 times more restrictive than the filter.

This is based on max oil pump supply pressure of 75 psi (relief setting) with a max measured engine oil pressure of 70 psi on my LS6.

Sound about right? Anyone got better data?

 

[SuperBusa]

I know Gary must have some data or info on this.

 

[Gary Allan]

If your LS oil pump is loose by design, then it's a YMMV situation. If you recall the guy with the high volume deal, he was using 5w-40 which just happened to have his idle pressure at his relief of (iirc) 45psi. He's the one that saw 5psi drop with using (again, iirc) M1 vs. K&N. If he had done the same comparison with 10w30 in the sump, then it could have been differentiated between a pump that was truly in relief ..or one that just was "loose" in terms of efficiency.

 

[edhackett]

Based on the Purolator data for hot oil flow earlier, I come up with 16:1 for a turbo Subaru.

Ed

 

[hofcat]

I am not sure just where oil pressue is meassured in most cars but if you can get a pressure reading in the oil supply line before the oil filter and another between the filter and the engine, that would give an indication of the relative restriction between the engine and oil filter. The difference between the two readings would aproximate the filter restriction and the reading between the filter and the engine would approximate the drop across the engine. Take the ration of those two numbers. This is assuming the oil sump is at or close to being at ambient pressure.

 

[Gary Allan]

 

[mechanicx]

Gary is that saying 4 psi pressure drop across the filter at 50 psi and full operating temperature or something else? I was curious about the oil, filter and application this is. and what kind of pressure drop do you see at cold start?

 

[SuperBusa]

Originally Posted By: hofcat
I am not sure just where oil pressue is meassured in most cars but if you can get a pressure reading in the oil supply line before the oil filter and another between the filter and the engine, that would give an indication of the relative restriction between the engine and oil filter.


Exactly right - that's how I see it too. Most cars have the engine's oil pressure sensor located between the filter outlet and the engine inlet. The oil inside the engine swirting out of all bearings and parts being lubricated and draining back to the sump is at zero gauge pressure (ie, ambient pressure) for all practical purposes.

Originally Posted By: hofcat
The difference between the two readings would aproximate the filter restriction and the reading between the filter and the engine would approximate the drop across the engine. Take the ration of those two numbers. This is assuming the oil sump is at or close to being at ambient pressure.


Yes, I agree. This is basically how I came up with the ratio in my first post, based on the fact that I know the oil pump's pressure releif valve is set to 75 PSI, and I see 70 PSI max (when the pump is in pressure relief at 75 PSI max) with hot oil when at sustained near redline RPM. I'm pretty confident the pump's pressure releif valve keeps the max near 75 PSI, even though there is no gauge before the filter to confirm this.

Based on the 5 PSI difference between the pump's 75 PSI max pressure relief setting, and the 70 PSI oil pressure sensor reading between the filter & engine, then this means there is a 5 PSID across the filter, and the pressure drop ratios become:

Filter PSID/Pump Max Press = 5/75 = 0.06667
Engine PSID/Pump Max Press = 70/75 = 0.93333

0.93333/0.06667 = 14:1

Engine is 14 times more restrictive than the filter.

So, looks like an engine is typically in the neighborhood of 14 ~ 16 times more restrictive to flow than an oil filter.

Originally Posted By: edhackett
Based on the Purolator data for hot oil flow earlier, I come up with 16:1 for a turbo Subaru.

Ed


Thanks for you date point Ed.

 

[Gary Allan]

Originally Posted By: mechanicx
Gary is that saying 4 psi pressure drop across the filter at 50 psi and full operating temperature or something else? I was curious about the oil, filter and application this is. and what kind of pressure drop do you see at cold start?


Typically it was 2psi or less. I don't recall the exact conditions of the one with the temp gauge included, but given the readings I'd say that it was a 15w40 after about 10 miles of driving and at a decent road speed. At idle that visc would probably ( again from fading memory) be something like 13-15psi. 30 weights produced 9-11 ..20's 5-7 and 10 weights showed near zero.

Here was one caught on the upswing to the relief limit. The lower gauge just starting to hang up ..and the upper (engine side) continuing on to the relief limit. As the relief eased closed, the differential compressed to the typical 2psi or less. This 2psi or less was maintained constantly (clean filter) as long as the relief on the pump was closed. That is, anything below 82psi. I don't know the volume capability of the oil pump.

By geeaea

 

[SuperBusa]

Originally Posted By: Gary Allan
If your LS oil pump is loose by design, then it's a YMMV situation. If you recall the guy with the high volume deal, he was using 5w-40 which just happened to have his idle pressure at his relief of (iirc) 45psi. He's the one that saw 5psi drop with using (again, iirc) M1 vs. K&N. If he had done the same comparison with 10w30 in the sump, then it could have been differentiated between a pump that was truly in relief ..or one that just was "loose" in terms of efficiency.


I think the LS1/LS6 oil pumps are pretty good performers and relatively high volume (10 - 12 GPM at max engine RPM). This engine only has 20K miles on it too. Other Vette guys have verified the typically see 70 psi max on their oil pressure gauges at high RPM, so it sounds like the pressure relief valves work fairy constantly on them too.

I haven't tired any other oil weights in this engine, only run the recommended 5w30 Mobil 1 ... but have used many different filters (WIX, Amsoil, PureONE) and see the same oil pressure with all of them).

 

[Gary Allan]

Then I'd imagine that there is no appreciable psid difference between filters if your indications are accurate. This pretty much parallels my observations.

The one guy's HV oil pump (for some odd reason) had some lower relief limit. He still reached higher pressures (like yours), but that had to be due to the relief port limits vs. the gross volume production from the pump.

 

[SuperBusa]

Originally Posted By: Gary Allan
Then I'd imagine that there is no appreciable psid difference between filters if your indications are accurate. This pretty much parallels my observations.


Yep ... if there were any differences between the various filters I've used, it was probably only +/- 1 PSI and I can only see 1 PSI increments on the digital oil pressure readout on the car. Any filter PSID differences were in the noise level.

Originally Posted By: Gary Allan
The one guy's HV oil pump (for some odd reason) had some lower relief limit. He still reached higher pressures (like yours), but that had to be due to the relief port limits vs. the gross volume production from the pump.


I don't recall exactly the details on that thread ... but yes, it was an odd situation. I agree that his HV oil pump was probably "over powering" the relief valve design.