[Eric_K]

If you are logging oil pressure, you may have a better picture of this. My stock pressure gauge goes to max past 5k rpm or so. I have no idea what is really happening past that. Do you see pressure linearly increasing all the way to 7k rpm? What does it go to - just curious? Does anyone know what pressure the oprv operates at? I would expect a lower viscosity oil to show less pressure - until the pressure is maxed. I need a data logger.

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[Renn68]

Stock gauge is not particularly accurate or linear - heres a plot I did a while ago of temp and pressure. Each colour is a different lap and the variation within a lap is due to change in pressure with rpm etc.







I couldn't lay my hands on the one I did of Mobil1 vs Redline

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[Eric_K]

That is interesting in that it shows the car warming up as you would expect. Pressure and temp seem to be stable after a few laps. I would like to see pressure plotted against RPM over a single lap (after the car is up to temperature). Do you have that data? I'm more interested in what the pressure is doing at certain RPMs.

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[Renn68]

yep - I can pull that data for you. I'll include some lat G and long G as well <img src="/forum/images/smilies/968/smile.gif" class="smilie" alt="" />



Gotta do some work before the weekend (2.30pm friday here) but will find some time over the weekend.



If you are inclined and wanted to play with the data, you can download the race studio software here http://www.aimsports.com/software/index.html and I'll email you some data files

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[Eric_K]

That would be awesome. My email is ejkrause (at) hotmail.com

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[Renn68]

sent

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[333pg333]

Renn, what oil are you using and what viscosity? You on the North or South Is?

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[333pg333]

[quote name='flash' post='33449' date='Mar 29 2007, 06:26 AM']i agree on the weight of oil - i'm sticking with the heaviest thing i can put in there - i know that formula 1 cars etc run a 5W oil, but they also run a new engine every race - we found in the datsuns and mgs that in order to spin the 8800 rpm the engines were capable of, we needed to stick with a heavier oil - the thinner oils would separate, leaving the bearing dry - didn't take long to spin one like that (keep in mind that this was over 15 years ago and oils were different then too)



we also had to do some work on the oil passages, like removing small obstructions and things that would cause turbulence in the flow - any little bumps in there and there was a chance of an air gap



i understand the idea behind the lighter oil, less resistance and better heat transfer, but it presupposes that the oil is always there - i think some work would probably have to be done on the oil passages to insure that this happened before changing to a lighter oil - if you could do that, i suppose you could have the best of both worlds - i haven't looked at the oiling system in this engine to see how tough that would be though - anybody have any thoughts or experience on this?



as for the windage tray, did it block the squirters? typically these things really do work - what was the specific reasoning behind its removal?[/quote]

Actually Porsche ran Shell straight 50w for years even when advertising a rival brand. We will stick with the higher weight for the buffering reasons as much as lubrication. There seems to be too much of a coincidence between 944/951's that have spun a bearing and low viscosity oil to ignore. Even though the oil is under pressure, gravity takes effect, moreso on a lighter viscosity as far as I understand. I guess d/sumping is still the answer.

As for the Windage tray. Well it didn't block the squirters as we don't have any on 951's although I'm looking into that in the next few days. A bit of a fiddly job especially after boring a lot of meat out of the block to fit the Mid Dartons. Without the w/tray, there is room for the crank to pick up and 'splash' some oil up underneath the pistons acting like a poor version of the p/squirters.

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[flash]

ah - got it - thanks

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[Renn68]

333 - Redline 20W50 in both the 44ts and the 68 - North Island - you're in the West Island right?

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[333pg333]

[quote name='Renn68' post='33541' date='Mar 30 2007, 01:14 PM']333 - Redline 20W50 in both the 44ts and the 68 - North Island - you're in the West Island right?[/quote]

Heheheh not bad bro, not bad. <img src="/forum/images/smilies/968/laugh.gif" class="smilie" alt="" />

I was down in the South of our summer retreat last year and it was made for driving our cars. I would seriously consider putting mine on a boat and come over for a driving holiday one day. Beautiful place indeed.

Good choice of oil too. We use Castrol of a similar weight but are going up to 60 this season.

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[Eric_K]

A big thanks to George for sharing his data file. I played around with the oil pressure data and the results are interesting. The data shows little correlation of pressure and RPM. Max pressure seems to happen when the throttle is lifted and RPMs are decreasing. I would have thought with a positive displacement pump that the faster it spins the greater pressure it would create. But that doesn't really show in the data. There are obviously many factors in play.



What I did expect to see, and was there, is that max pressure occurs at the same place. The tops of the pressure graph are "clipped" and flat. I think that could indicate the OPRV is coming into play.



Here is a graph I did. It shows RPM, throttle & oil pressure during George's fastest lap.

   

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[Eric_K]

I got the graph added now. See above.

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[Renn68]

Heres another view of the same info - rpm on the x axis, oilP on the top and OilT on the bottom.



Green - Lap 2 shows an incr ip OilP from idle to ~3500rpm then plateau

Blue - Lap 3

Red - Lap 10



As OilT increases, OilP decreases which is what you would expect at constant volume.



Its the pressure plateau from 3500 to redline that has me puzzled where volume increases (with rpm) but theres no change in pressure or temp.

If a relief valve was coming into play, I wouldn't have expected the drop in the plateau from lap 2 to lap 10 ..........hmmmm

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[flash]

i think it makes sense - as an example of how this worked on a different car, max pressure was set by the OPRV - didn't matter what you did, that was as high as it got - there was a minimum rpm to get there though, but over that made no difference - the pump may have been outputting more pressure at the higher rpms, but the valve relieved it



then later, when things got hotter, the pressure would drop, and on an older engine, with an older pump, it would drop below the valve setting



that may be what is happening here - the OPRV might be right about at the pressure of the engine when hot, so it shows a ceiling when cold, then lower pressures, below the valve setting when hot



another explanation could be that the valve itself may be changing limits as it gets hot - if it is a spring, like it was in this other car, it could be heating up and getting weaker, thereby lowering the effective pressure ceiling



is the OPRV external? we had to keep changing springs every season to keep it accurate, but fortunately it was external and took 30 seconds to change

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[Eric_K]

The data brings up more questions than answers.



[edit]

The OPRV is on the side of the engine below the filter. Yes, it could be affected by warming up too. The max pressure falls by about 10% as the engine comes up to temp.

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[333pg333]

Well those graphs would make Jackson Pollack happy. lol

So if we're dealing with an OPRV that varies it's movements based on heat and age then it seems a bit tricky to get a true indication of what's happening but this is pushing my understanding somewhat. I think that I'll feel more insurance once the d/sump goes on all the same.

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[Renn68]

yep - a dry sump would be nice. I won't scare you with the plot of pressure vs lat and long G's

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[333pg333]

You know there are some people in this world who get just a little bit excited when you talk like that!

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