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That is weird, do you know if it's at all common to the 4b11? I'm not setup to do oil pressure logging on my X, otherwise I'd go see for myself.
Not many rev past 8k. Years back there were a couple that shimmed the oil pump to allow higher oil pressure but it still dropped pressure past 8k. I'm not too concerned as the pressure never drops below a bad number but I have always been curious what causes the drop.
I log oil temp and pressure from the oil filter housing.
One of the latest Engine Masters episodes just dealt with oil filters. The jist of the episode was that some filters do flow a tiny bit more and have slightly different pressure loss figures, but ultimately all oil filters, big and small, are pretty close in overall flow and pressure figures. Check the MotorTrend site for the full episode, there is a lot of interesting science behind it.
Not many rev past 8k. Years back there were a couple that shimmed the oil pump to allow higher oil pressure but it still dropped pressure past 8k. I'm not too concerned as the pressure never drops below a bad number but I have always been curious what causes the drop.
I log oil temp and pressure from the oil filter housing.
One location where oil pressure is increasing at high rpm is at the rod journals. Oil is literally being vacuumed out of the mains by centrifugal force.
One location where oil pressure is increasing at high rpm is at the rod journals. Oil is literally being vacuumed out of the mains by centrifugal force.
^This
I've been doing a bunch of research around this.
So the higher the RPM, the harder it is for the block to feed the mains galley in the crankshaft.
Because the crankshaft is spinning at a fast rate, it's trying to repel the oil flowing into the oil gallery in the crankshaft with centrifugal force.
And the oil at the rod bearing is actually being flung/sucked out by the same force.
So you need to have enough oil pressure at the mains to keep the rod bearings lubricated.
If there isn't enough oil pressure, the suction will actually cause the mains bearing to suck in air.
@razorlab I think the small drop in oil pressure at high rpm is the extra "usage" of oil from centrifugal forces which exceeds what the pump can supply, so that's why there is a small drop in pressure. I'm still working on this, but it's what I have come up with so far. I could be wrong.
Well that settles it for me.
New oil filters - different sizing makes no difference to pressure loss across the filter.
Testing below is of the small non-bypass filter I could find.
Exactly the same as the Wix 51515XP filter.
You could actually setup a "change oil filter" warning when the pressure differential (PSID) grows.
But until then - just use whatever sized filter you want.
Excellent and interesting stuff you've got here. It would appear that 'high flow' racing oil filters are a gimmick for any engine that can supply adequate oil pressure.
Well that settles it for me.
New oil filters - different sizing makes no difference to pressure loss across the filter.
Testing below is of the small non-bypass filter I could find.
Exactly the same as the Wix 51515XP filter.
You could actually setup a "change oil filter" warning when the pressure differential (PSID) grows.
But until then - just use whatever sized filter you want.
Not surprised...nice work. I know it really doesn't matter, but wonder if you have a way to test how much of that pressure drop is from the flow through the housing itself. I am guessing it is a majority of that pressure loss.
This story is embarrassing to tell. Years ago I drove beautiful 1992 6 -4 combo DSM. I purchased it new. In those days you could still buy oil for less than a dollar a quart. I won't mention the brand of oil I used (Mobil) but at the time there was a good reason for its low low price, no detergent. I changed oil every three thousand miles and I started to notice something, a pattern that kept repeating. For the first 1500 miles or so the oil would stay clean and the engine would be quiet. Then suddenly the oil would be black and the lifters loud. Eventually, when the car had no power, I had to replace the lifters and that was when I opened the engine to discover that on the inside it looked like a well used ash tray. So, I think I was causing the filter to plug and go into bypass in as little as 1500 miles. Mobil announced new and improved oil "now with more detergent" but I switched brands anyway.
Since then I randomly switch oil brands and oil filter brands. I don't trust anybody anymore. I figure if I get crap oil or crap filter at least it is in use for only three thousand miles. That and I run an over sized filter.
Not surprised...nice work. I know it really doesn't matter, but wonder if you have a way to test how much of that pressure drop is from the flow through the housing itself. I am guessing it is a majority of that pressure loss.
Yup I think just the turns the oil needs to make it the actual reason for the pressure drop.
Originally Posted by barneyb
Since then I randomly switch oil brands and oil filter brands. I don't trust anybody anymore. I figure if I get crap oil or crap filter at least it is in use for only three thousand miles. That and I run an over sized filter.
Yup from what i've seen - just run the filter with the best efficiency and capacity that has the "most trusted" construction and you'll be fine.
It would have been interesting to change only the filter in that old scenario to see if it fixed the problem!
This story is embarrassing to tell. Years ago I drove beautiful 1992 6 -4 combo DSM. I purchased it new. In those days you could still buy oil for less than a dollar a quart. I won't mention the brand of oil I used (Mobil) but at the time there was a good reason for its low low price, no detergent. I changed oil every three thousand miles and I started to notice something, a pattern that kept repeating. For the first 1500 miles or so the oil would stay clean and the engine would be quiet. Then suddenly the oil would be black and the lifters loud. Eventually, when the car had no power, I had to replace the lifters and that was when I opened the engine to discover that on the inside it looked like a well used ash tray. So, I think I was causing the filter to plug and go into bypass in as little as 1500 miles. Mobil announced new and improved oil "now with more detergent" but I switched brands anyway.
Since then I randomly switch oil brands and oil filter brands. I don't trust anybody anymore. I figure if I get crap oil or crap filter at least it is in use for only three thousand miles. That and I run an over sized filter.
I'm sure you know this now, but in case anyone doesn't, non-detergent oil (hard to find) is only for engines, or devices, that don't have an oil filter- lawn mowers, most air compressors, etc. And, I'm unfortunately old enough to remember that in the 1980s you could buy Exxon Superflow detergent oil for 89-99 cents a quart.
The main purpose for the bypass on filters is primarily to provide a means for burst protection on the filter. The secondary purpose is to allow oil flow in the event the filter becomes clogged. People always get spooked that their filter is bypassed and the engine isn't getting filtered oil, but that's RARELY ever the case.
As to the centrifugal force keeping the main gallery from being supplied I don't buy that at all. The mains are fed from above, where there is the least amount of loading on them and the groove in the upper bearing halve is there as a means to allow greater flow to reach the lower bearing where most of the load is handled. Rod journals have a tougher time with centrifugal force on through drilled cranks (like stock) but cross drilled cranks (Callies, Manley, and a couple others) don't have this issue and centrifugal force actually pulls oil to the rod.
Some things to note about crank oiling design. Cross drilled cranks require great attention to detail, they have a large potential for a stress riser to form on the ovate exit hole for the rod journal, this is why Manley cranks have a bad rep for cracking. Though drilled cranks don't have this dilemma because all the holes are straight through so there is no ovate shape and no thin cross section for a stress riser to form, this is why Eagle and stock cranks have been taken well into the quadruple digits reliably.
If you're building an engine with a cross drilled crank, I would highly recommend you pay your machinist/engine builder extra to detail the crank and radius all the oiling holes.
As with most things in racing, there is a give and take and in this case it's oil supply vs rigidity.
