[Skipping preamble because I think we have the context in this thread]
In this post, I’m going to share multi-channel data logs from a recent track day and provide some commentary. I’m still intending to share raw files at some point, but I want to walk through some of the laps in a more guided way first.
Why? Well, it’s very easy to arrive at incorrect conclusions if you misinterpret the data. For example, you will see expected pressure drops at low RPM. Imagine you’re going 100 mph but you put the car in neutral. The engine RPM will fall to idle regardless of the speed and your oil pressure will drop as well. But there is no harm being done to the engine because it’s not under any meaningful load. But if the RPM is above roughly 4000 and you see a pressure drop, that is not expected.
The track is Thunderhill 5-Mile Double Bypass, which is composed of:
- The first 9 turns of Thunderhill East
- A connector which spits you out onto Thunderhill West after T2W
- T3W through T7W
- You bypass turns 8-10W and take the West pit straight into T1W
- Finally, you take another connector and rejoin East before T10E
Driver: Joe McGuigan
Pace: 3:28.977 & 3:30.262
Joe is a very quick driver and was driving in a session with very little traffic, so he was able to do an outlap, put in two fast laps, and then do an in-lap. You can see more of him driving on his YouTube channel. I also posted these two laps on my channel here. One thing to keep in mind is the scale for the oil pressure telemetry on that video is from 0-100 so the magnitude of the pressure drops don't look as significant in that video as they really are. The absolute PSI number displayed is the same and that is more useful with that scale. I updated this scale to go from 20-70 psi in my video from earlier this week.
These laps give us a great view at how repeatable the pressure drops are. Oil pressure is the third trace from the bottom. From left to right we have:
- T3E: Major pressure drop to 28 psi
- T5E (Easy Bypass): Major pressure drop to 27.4 psi
- T9E: Moderate pressure drop to 45 psi
- T9C: Moderate pressure drop to 37 psi
- T5W: Major pressure drop to 26 psi
- T6W Entry: Moderate pressure drop to 40 psi
- T1W: Moderate pressure drop to 42 psi
- T14-15E: Major pressure drop to 30 psi
(You can open this image in a new tab to see it full scale)
Driver: Brian Armstrong
Pace: 3:40 and 3:33 (4 laps from 2 sessions)
Up next we’ll look at some of my laps. Here’s where I have to practice some humility. Remember in the video when I said I was a beginner/intermediate driver?
Okay first some excuses: This was my first time lapping Thunderhill 5-Mile. Previously, I had done 1 day at Thunderhill East and 2 days at Thunderhill West. And its was hot haha.
But more seriously, the 7 second difference between the first session and the second session depicted here is explained by me riding along with Joe in between the sessions. Once you experience the actual limit of the car, you feel more comfortable pushing harder.
This data is quite useful because we can compare essentially a beginner driver doing 3:40 to an intermediate driver (same driver, but with more confidence) doing 3:33. The representative beginner driver is orange/red and the intermediate driver is magenta/purple.
In both of these sessions I’m able to observe pressure drops, but they are more severe at the 3:33 pace. I have a pressure drop down to 25 psi on the orange lap but on the magenta/purple laps the lowest pressure I see is 30 psi. The duration of the drops for the 3:40 pace are also shorter.
Note that there is a large pressure drop toward the end of the trace (which is the braking zone for T14E). This is not a concern because if you look at RPM, it drops very low. Essentially, I’ve messed up my braking and let the engine RPM drop too low. I’m effectively in neutral here, which shows up on the Gear trace as well.
Next up, we’ll look at a comparison of my best lap vs Joe’s best lap, so you can see me representing the intermediate driver vs Joe’s lap. You can see that being a slower driver is resulting in fewer pressure drops and the drops have a shorter duration. Of course, this is intuitive and is the same reason why I’m not very concerned about people who are driving these on the street unless they’re really pushing the limits of the car’s grip.
Okay, last I dug up a recent autocross session and I am able to see meaningful drops here as well. Note that the total duration of the “lap” is only about 1 min, so these pressure drops have a short duration compared to the ones we see on the track. Also, the “lap” times would be more consistent if I had set the Aim up to be in point-to-point mode rather than the mode where it attempts to learn a circuit. I couldn’t find a way to switch that.
At the upcoming test this weekend, we’ll be at Thunderhill 5-Mile again. This time we’ll be using the Cylone/Bypass configuration, so we will have a different turn replacing T5E. We will ask the organizers to allow Joe to run a few laps of by Double Bypass configuration during lunch for more consistent data, but no promises. If we aren’t able to reproduce the test on the same track layout, we will omit T5E from our findings, but we will still be able to compare the rest of the turns. A reminder that these tests are self-funded, so we can’t always control all the variables.