Another Oil Pressure data point

#1

Here is my OP chart from a lap of CMP this weekend. The lowest my OP (at the pump) dropped each lap was to ~35psi at turn 11. But the data is flawed because I didn’t have the traction to pull high g’s. So folks with better tires might have been dropping to down to 28psi.

35psi represents a 20psi drop, 30% more equals a 27psi drop. 55psi-27psi = 28psi. The 30% comes from pulling 1g instead of 1.3g.

I’m not saying that 28psi is the result of a rigorous analysis, but it’s probably in the ballpark. 6 months ago I would have predicted that OP would drop to a third of that, but the data from several tracks has failed to bear that out.

I don’t know if 28psi near redline rpms will often cause the loss of bearing material. I know that if I had 28psi at high rpms on a straight-away, I’d be thinking “uh oh”. But there is no certainty that brief drops in OP, of only moderate severity, cause premature bearing wear. Some anectodal evidence sure, but no certainty. [file name=OPChartCMPNov09.jpg size=87915]http://spece30.com/media/kunena/attachments/legacy/files/OPChartCMPNov09.jpg[/file]

#2

That looks like good news. Can you plot RPMs, lateral g’s and oil pressure on one graph?

Arguably, the loss of pressure (30% going from 1.0 to 1.3 g’s) is not actually linear when plotted against horizontal g’s because vertical g’s remain relatively constant at 1. Or - even better from an oil pickup standpoint - increase above 1 as you get compression (e.g. Turn 1 at Road Atlanta). Those vertical g’s in excess of 1 will help oil stay in the bottom of the pan.

#3

The RPM’s are key. G’s are nice, but if the motor is making 30 psi at 3k that is on par with what you’d expect.

30 psi at 6k or 30 psi at 500 is a different can of worms.

#4

Steve D wrote:

[quote]That looks like good news. Can you plot RPMs, lateral g’s and oil pressure on one graph?

Arguably, the loss of pressure (30% going from 1.0 to 1.3 g’s) is not actually linear when plotted against horizontal g’s because vertical g’s remain relatively constant at 1. Or - even better from an oil pickup standpoint - increase above 1 as you get compression (e.g. Turn 1 at Road Atlanta). Those vertical g’s in excess of 1 will help oil stay in the bottom of the pan.[/quote]

My rpms didn’t record. I probably have a loose wire.

Sure, my 30% is a swag, but the data shows that I was definately 20-30% low on lat g’s, and since we’re just looking at “ballpark”, assuming a linear relationship over a small range of numbers seems a decent approximation.

I don’t know if I buy the vertical g’s argument.

Increased grip (vertical g’s) due to elevation change only occurs when the “rate” of elevation increase changes. Not when the elevation increases. For example, when the road pitches up the car compresses and you have extra grip for a heartbeat. But that doesn’t mean extra grip all the way up the hill. You only get the extra grip for that heartbeat that the road pitches up.

Gravity is acceleration. When degree of the inclination changes, acceleration occurs. But driving up a hill isn’t acceleration.

A constant elevation banked curve is something different, but I don’t think that would make the data less valid either.

Re. rpm. The OP loss is not about rpm. You don’t see OP loss in too many right turns. I agree that we are often at lower rpms in turns, but I’d guess 3800 is about as low as most folks want to get, and 4500rpms at high g is probably common. Is 28psi ok for 4500rpms? We’ll probably never know for certain.

#5

Ranger wrote:

Sweet! If we’re just ballparking it, I’d say the typical M20 engine has roughly enough oil pressure to run for approximately 2-3 seasons of normal track use between bottom end refreshes. :laugh:

Agreed, but Turn 1 at RA is more than a heartbeat. Unless you drive as fast as Johan. Or 1.5 heartbeats for Robinson. :stuck_out_tongue:

#6

This will sound like a shameless plug, but it is not. I ran Paul Poore’s modified stock pan at the ARRC last weekend, and at turn 5 (1.4gs) my OP went from 55 to 40, but never below, and held steady all the way up the hill while tracking out. At the top of the hill, it came back to 55, at about 5200rpm. I run 10W30 racing oil, so mine is more fluid than most. And, yes, I do run one quart OVER FULL. I think this pan will help bearing problems. Chuck

#7

Chuck, Just curious, what modifications are made to the pan?

#8

I’d agree that 2-3 seasons is reasonable, but I’m just pulling that number out of my butt. All we have to go on is a small body of anectodal evidence, and not a helova lot of agreement in what we have.

I’d agree with Chuck on his modified oil pan approach. Not that he ought to give a shit re. my agreement, given that he has vastly more experience in all of this then me. Back when I was obsessing over this I talked to oil pan guys and circle track guys. We’re a minority in that we’re trying to race cars that have no oil pan baffle improvements. Those guys would think that we’re crazy.

The oil pan’s advantage is simplicity, but I think that an Accusump can be put in for less $$. My sump and plumbing cost <$200.

Maybe the next couple of years will provide clear evidence that Accusumps and baffled oil pans result in significantly better engine longevity. Only time will tell.

#9

The stock pan is mounted in a mill, and the bottom is removed. A “T” sump with trap doors is fabricated and welded to the stock remaining pan. Seems to work very well…does not leak, which is more than I can say for the pan I made. The real test will be RR in April. CB

#10

Does the modified pan increase the engine oil capacity?

#11

Yes, my pan is 7qts not counting the oil cooler and remote filter…total for mine is 8.5qts. Note, that is not with the 1qt over. CB

#12

So I guess it stands to reason with 9.5 quarts of oil, your OP would be a little higher than a stock configuration. It also occured to me that the hash mark on your oil stick is probably meaningless with a modified pan, oil cooler and remote filter. Agree?

#13

Gasman wrote:

More oil in the pan doesn’t mean more OP. OP is set by the amount of pressure the pump can sustain at a given flow rate. Flow rate is set by the viscosity of the oil, it’s flow restriction and the pressure applied.

Exceptions are loss of oil flow when the pump pickup becomes uncovered, or when oil is cold and hard to pump.

It might still be logical to use the marks on the stick. A person could think of it as a reference distance below the crank, instead of OEM calibrated oil in the pan. One might get deeper into that issue tho by asking themselves…Why do we have extra oil in our pan? The various answers to that can guide a person on how much oil to put in when they’ve either created a bigger pan or put in an Accusump. For example, it now takes 7.5qts to get me to the Full mark on the stick. But I don’t bother to overfill 1qt any more. The sump will take care of oil flow when the pickup goes dry.

And we do know that the oil pump pickup goes dry, that’s not longer a question. That’s why the OP drops. But my data seems to say that the pickup goes dry only briefly such that OP drops to the 20’s. That can’t be nearly as bad as if the pickup ran dry long enough for OP to drop to 0 briefly.

Steve, you gonna yell at me some more now?

#14

Scott, No, I’m done. The first sentence of your post being false, didn’t see any reason to try and argue the rest of it.

#15

Gasman wrote:

Ok.

I tried in this post to explain why the different shaped pan that holds more oil won’t affect steady state OP, but each attempt just sounded patronizing. So I deleted it all and I should leave it at “ok”.

Consider this question tho. Where is the water pressure highest…2" deep into a bath tub, or 2" deep into a lake? The answer is that they are the same. And that’s why larger oil pans don’t increase static OP.

Filling a qt high would increase OP, but not enough that we’d notice.

Talk to another engineer if you don’t like my answer.

#16

Ranger wrote:
Consider this question tho. Where is the water pressure highest…2" deep into a bath tub, or 2" deep into a lake? The answer is that they are the same. And that’s why larger oil pans don’t increase static OP.

Filling a qt high would increase OP, but not enough that we’d notice.

Talk to another engineer if you don’t like my answer.[/quote]

To answer this question, I will need to know how much compressed air is holding the lake and bath tub water in place.

By the way, which railroad do you work for? :wink:

#17

Ranger wrote:

Gasman wrote:

Actually, it is true unless you read too much into it. More oil in the pan does result in more OP (i.e. higher average OP and fewer “drops” ) if that greater volume lessens the number and duration of times the oil pickup is dry. I can’t say with 100% certainty that more oil results in higher average OP, but I’d bet a lot of money on the hypothesis.

Gasman wrote:

[quote]To answer this question, I will need to know how much compressed air is holding the lake and bath tub water in place. [/quote] Approximately 14.7 psi. Your answer please? :wink:

#18

Steve D wrote:

[quote]Ranger wrote:

Gasman wrote:

Actually, it is true unless you read too much into it. More oil in the pan does result in more OP (i.e. higher average OP and fewer “drops” ) if that greater volume lessens the number and duration of times the oil pickup is dry. I can’t say with 100% certainty that more oil results in higher average OP, but I’d bet a lot of money on the hypothesis.
[/quote]

The oil pump pickup sucking air exception was already addressed above. Steve(G) seems to be saying that a deeper or wider pan results in more OP at the pickup.

#19

Ranger wrote:
[quote

More oil in the pan doesn’t mean more OP. OP is set by the amount of pressure the pump can sustain at a given flow rate. Flow rate is set by the viscosity of the oil, it’s flow restriction and the pressure applied.

Exceptions are loss of oil flow when the pump pickup becomes uncovered, or when oil is cold and hard to pump.

[/quote]

I think the idea of a higher capacity pan and the baffles is to keep the loss of oil at the pump pickup to a minimum. The fluctuating oil pressure you see is due to that, and its happening in every race engine in use. Static oil pressure is not even worth considering. So really, more oil in the oil pan, especially Chuck’s pan, does mean more oil pressure overall. Except of course, when you’re parked in the pits or driving in a straight line at low rpm.

I don’t see anyone disagreeing here. Sounds like we’re all saying the same thing.

#20

cwbaader wrote:

chuck,

what configuration are you running that pan in? i.e. are you running a crank scraper as well and/or accusump?

tks,

-kish