Weston Posted April 21, 2009 Posted April 21, 2009 Is it right turns or left turns that are supposed to be more prone to oil starvation for 944's? I logged my stock oil pressure sender this weekend and found that it had a lot in common with the G-force plot, especially in right turns and when immediately preceded by a left turn. I'm now wondering if this is really a drop in pressure, or if this is just because the oil pressure sender is on the right side of the engine and the G-forces are pulling oil away from it or affecting the sensor mechanism itself. There are some instances where it seems to go up a little in left turns, but it's so small and the pressure is already so close to maximum that it's hard to come to any solid conclusions. The correlation between the G's and the oil pressure seems to increase each lap, so I'm thinking that's temperature related. Here's the data that shows it the most, from my '84 engine with a 951 external oil cooler... (negative G's are right turns) All of the downward spikes in pressure were for only a fraction of a second and most of them occur in other laps as well. The sharpest one was from 4.4 bar to about 2.8 in Turn 11 at High Plains Raceway, which was the worst I can recall seeing all weekend (everything else didn't get below 3.0 bar and wasn't as sharp). I'm not really worried about it at this point, since this apparently happens to all of us with early oil pans and this is just the first time that I've logged it, but it could be useful to hear some thoughts on how solid the data from this sensor is... By the way, for anyone wanting to log this themselves, the electrical specs on the stock sensor in my '83 is that the wire going into the stock oil pressure gauge reads 1 volt when the gauge shows 0 bars, and 6 volts at 5 bars. At zero volts, the gauge reads below zero bars; that's why it jumps up to zero when you turn the ignition on. Quote
laze1 Posted April 21, 2009 Posted April 21, 2009 This would make a great commercial for the Canton Accusump... Quote
Andrie Posted April 21, 2009 Posted April 21, 2009 Looks to me it is related to RPM. Seem normal. What's the logging rate on the oil pressure? Seem to me there are lots of noise. Quote
dmdirks Posted April 21, 2009 Posted April 21, 2009 Definitely interesting data, Weston. Thanks for posting. There seems to be a correlation to g-force, but there may be some contribution from RPM also. Determining instrumentation error would be useful. As you mention it's not known how the oil pressure sensor responds to the g-forces imposed by the car. It may be worthwhile to try remotely locating the sensor in the car in effort to minimize mechanical and electrical noise. Is 40Hz the maximum sample rate? Can you overlay the three plots onto eachother? Quote
Weston Posted April 21, 2009 Author Posted April 21, 2009 Is it related ot G's or RPM? Both, and that's why I included the RPM plot, but G's are definitely a factor. There are spots where the pressure drops when I have both a 1G right turn and a drop in RPM from braking, so it's unclear which is the primary cause there, but then there are other turns where RPM didn't drop and the oil pressure still did. There's a strong link between RPM and oil pressure below 4000 RPM, but once you're above it, it's already near max pressure so that relationship becomes minimal. Quote
Weston Posted April 21, 2009 Author Posted April 21, 2009 It is logging at 40Hz, which is Traqmate's maximum. Here is RPM -vs- oil pressure... And here is G -vs- oil pressure change from average... So, although RPM is a factor, there are spots where RPM dropped for a left turn but oil pressure didn't do much, as well as spots where RPM dropped for a right turn and oil pressure dropped more than normal for that RPM level. I seem to recall two holes that I may be able to mount the oil pressure sender in (one on the right that has the sender, and one on the front that just has a plug), but I don't know if there is physically enough room to use the front location with the 951 oil cooler setup. Quote
944-Spec#94 Posted April 21, 2009 Posted April 21, 2009 Looks more RPM related since when the RPM's drop so does the pressures. The G loading looks to close, but you can see that in sustained G loading the oil pressure comes back even if the G's remain. Then when you consider the RPM change it seems to drop as there is drop in RPM and then both track similar on the way out. Quote
Litespeeds Posted April 22, 2009 Posted April 22, 2009 From our knowledge in NorCal, the big long left hand turn 2 at Thunderhill is the killer on our engines. Quote
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