After our last test session, we weren't comfortable with the pressures and temperatures we were seeing on our unmodified car. We were running Motul 300V 0W20, and pressures were dropping below 5 psi in the pits at the end of the session. Oil temps as reported by the ECU were well over 270°.
For today's session, we switched to 300V 5W30 to see if we could keep the hot pressures a little higher. Here's a graph of what we found.
This shows psi per thousand RPM at varying oil temperatures. As we'd expect, the hotter the engine, the thinner the oil. This is normal. The red line is the "safe" goal of 10 psi/thousand RPM. That's not an especially scientific value, just something to compare as "good/bad."
RPM values below 1000 RPM were excluded to get data from only when the car was actually moving. We're not interested in heat soak right now, just on-track numbers.
The blue is the 0W20, and the yellow is the 5W30. You can see pretty clearly how the 5W30 helped keep oil pressures higher as temperatures increased, but didn't really give us abnormally high pressures at lower temperatures. Both tests were run on track here at the Motorsport Ranch, with ambient temperatures around 85-90F.
We may run 5W40 for the next oil change just to see if that moves hot pressures higher, but we think it's safe to say 5W30 is the right call for tracking a relatively unmodified car in hot climates.
Anyone have any similar experiences?
Update Aug. 30
Here's an updated graph showing the same data and processing, once an oil cooler is added to the system (green series). You can see the oil still behaves as it always has, but it's kept about 30° cooler.
Now that we've seen how well it works on our car, we'll definitely be pushing everyone to run an oil cooler if you're tracking your car in the summer. As much as we love doing engine swaps for people, we'd rather not do it because someone spun a bearing from letting their oil degrade.