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Oil pressure at the head vs block

 
Old 06-28-2018, 02:40 PM
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Default Oil pressure at the head vs block

Hey guys I searched and couldnt find an answer. I know most everyone uses the block sending unit location for an aftermarket oil pressure gauge, with some kind of adapter like the trackspeed unit or similar. I was going to go this route as well, but the trackspeed unit wouldnt work with my sender for my prosport gauge. So I mounted it at the oil gallery port on the drivers side of the head that some people use for an oil feed for the turbo. I know there has been much talk of if this is a safe spot for an oil feed with some people saying because there is a restrictor you shouldnt use it, etc. I just recently installed my built motor, boundary stage 1 w/ 2 shims. Oil pressure off this port with 15w40 rotella dino for break in miles is 55-60psi cold idle, 15-20psi warm idle. 3k crusing i see 60psi cold, 30-40psi warm.

Curious if the head is showing less oil pressure than had I mounted this on the block instead but for anyone wandering what the OP at the head is thats what Im seeing.
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Old 06-28-2018, 04:12 PM
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Those numbers dont look too far off from what im seeing at the stock location with an innovate setup. I have a stage 2 pump with either 1 or 2 shims. 5W-30 break in oil. Obviously my setup is different than yours, but those numbers are certainly healthy.

My VVT isnt enabled yet so im sure my numbers will drop a bit when i do that.

Last edited by ridethecliche; 06-29-2018 at 09:07 AM.
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Old 06-28-2018, 04:43 PM
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I see those numbers with no shims in a BE pump on the stock location. My engine is also built a little loose too, on Royal purple oil. So numbers look good to me.
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Old 06-29-2018, 10:04 AM
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Its good to know Im in line with what others are seeing. I was thinking the pressure at the head might be less since its at the top of the engine and its flow restricted as well. I also have a small oil leak from what appears to be the hex screw on the oil pump, looks like its coming out of there and getting blown backwards when I drive. Feels wet also slightly behind that screw as well, I was second guessing myself and thinking somehow I forgot the pump O-ring but I know for a fact that I put that on there and i used RTV on every spot the FSM calls for. If I had forgot to install that O-ring I bet the leak would be VERY bad and my oil pressure would probably also be extremely low.
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Old 06-29-2018, 10:35 AM
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Pressure drop across an orafice is a function of flow. The pressure on both sides will be equal at zero flow. This is why IMO the whole turbo source from the head thing is .... bad

In a stock configuration, I don't think much oil is actually flowing through the head. I have no proof of this, so it is only an opinion.
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Old 06-29-2018, 10:37 AM
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Pressure should be in the ballpark as long as it's not after a restriction. If you were measuring pressure post something like VVT, it would be lower, but if you're measuring the oil pressure on the way to the head then the drop shouldn't be that substantial.

Edit: Flow and resistance, right Ted? Anything requiring work should drop the pressure even though the flow should remain consistent.
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Old 06-29-2018, 10:45 AM
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Flow is essentially current, pressure is voltage, restrictor is resistance. The is a restrictor in the block side of the head oil feed. Increasing flow from the head side of that restrictor will result in lower head pressure. The actual equation for flow across an orafice contains a square term IIRC, so it doesn't necessarily follow rhe universal equation, Ohm's law.
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Old 06-29-2018, 10:45 AM
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Originally Posted by ridethecliche View Post
Pressure should be in the ballpark as long as it's not after a restriction. If you were measuring pressure post something like VVT, it would be lower, but if you're measuring the oil pressure on the way to the head then the drop shouldn't be that substantial.

Edit: Flow and resistance, right Ted? Anything requiring work should drop the pressure even though the flow should remain consistent.
wat
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Old 06-29-2018, 11:16 AM
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Originally Posted by Ted75zcar View Post
Flow is essentially current, pressure is voltage, restrictor is resistance. The is a restrictor in the block side of the head oil feed. Increasing flow from the head side of that restrictor will result in lower head pressure. The actual equation for flow across an orafice contains a square term IIRC, so it doesn't necessarily follow rhe universal equation, Ohm's law.
Ah, didn't realize that to be the case.

And womp, it's bernoulli's at play not just simple V=IR, right?
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Old 06-29-2018, 11:18 AM
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Right
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Old 06-29-2018, 11:36 AM
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Originally Posted by Ted75zcar View Post
Flow is essentially current, pressure is voltage, restrictor is resistance. The is a restrictor in the block side of the head oil feed. Increasing flow from the head side of that restrictor will result in lower head pressure. The actual equation for flow across an orafice contains a square term IIRC, so it doesn't necessarily follow rhe universal equation, Ohm's law.
So can I deduce that the pressure at the head will be slightly lower than the pressure at the block where the factory sending unit is?
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Old 06-29-2018, 12:09 PM
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Yes, oil flows through the head, so you will necessarily see a drop in pressure. What that drop is? No clue. A pressure transducer has no flow, so it at least doesn't change the head pressure. I believe the change in pressure loss goes with the square of the flow, so if you double the flow, you quadruple the loss. Oil properties will play in as well. Rest assured a whole bunch of science went into the design.
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Old 06-29-2018, 12:30 PM
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Originally Posted by Ted75zcar View Post
Yes, oil flows through the head, so you will necessarily see a drop in pressure. What that drop is? No clue. A pressure transducer has no flow, so it at least doesn't change the head pressure. I believe the change in pressure loss goes with the square of the flow, so if you double the flow, you quadruple the loss. Oil properties will play in as well. Rest assured a whole bunch of science went into the design.
Good stuff Ted, thanks for your input. Appreciate your knowledge. I may down the road stick a sender on the lower block port and see what kind of pressure drop Im seeing.
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