N54 Oil Pressure Transients on Track

[fe1rx]

As part of my AiM MXS 1.2 Dash Logger installation I installed an oil pressure sensor and began logging oil pressures on track last year.

https://www.1addicts.com/forums/show....php?t=1801907

Unlike the N55, which has an oil pressure transducer, the N54 is only equipped with a low pressure warning switch and idiot light. The N55 has a reputation of extremely low oil pressure transients on track, which has motivated some to install Accusumps.

https://www.1addicts.com/forums/show....php?t=1752666

What is normal oil pressure? I plotted oil pressure against rpm from cold start to fully warmed, keeping rpms below about 3000 rpm until the oil was warmed up.



Before the oil was warm oil pressure was 85 – 90 psi above 1000 rpm. Once the oil reached 60°C the oil pressure vs rpm curve had settled down to a characteristic curve with two knees. This confirms that once the oil reaches 60°, the engine can be considered to be “warmed up”. The characteristic curve is represented in simplified form below.



If it strays far from that curve under track conditions, I would consider that noteworty.

So what I have found?

I began by choosing 3 representative fast laps from different events and plotted oil pressure against rpm. What this reveals is that rpm never drops below 3000 rpm and normal oil pressure ranges from 75 to 90 psi. There are numerous transient occurences of lower pressures, down to about 35 psi. These event do not appear to be rpm related as they occur widely over the range of rpm values.



I next looked at the same data vs position on track to see if the transients occurred at specific track locations. There is definitely variation lap-to-lap.



Looking at the same data vs lateral acceleration confirms that the transients occur primarily at high lateral g.



The above graph suggests that extreme braking does not induce the transients very strongly, and the next graph of oil pressure vs longitudinal acceleration confirms this.



To get a better idea of the accelerations in question, we can plot a friction circle for the three laps.



While the scatter plots above provide and idea of how widely the oil pressure varies, it does not show what exactly triggers a transient event, and how it progresses. For that, we look at a single fast lap against track position, identifying each major transient event with a colour code.



Then for each transient event, we plot oil pressure against lateral acceleration, as the acceleration rises and until the transient begins, using the same colour code.



Here we can clearly see that the trigger is lateral acceleration approaching 1-g. Once triggered the oil pressure becomes random. It appears that high lateral g is required to trigger a transient event, but that oil pressure does not necessarily imediately return to normal as the lateral acceleration eases. While this track has more right turns than left, left turns are more prevalent, and longer lasting

The upper right corner of the track map below is turn 1, and the track runs clockwise.

[Dieselboy]

Are you using an accusump, baffles, etc?

[fe1rx]

Originally Posted by Dieselboy

Are you using an accusump, baffles, etc?

I should have clarified, oil system is stock. Using Mobil 1 0W40. No baffles or accusump.

[bbnks2]

Originally Posted by fe1rx

I should have clarified, oil system is stock. Using Mobil 1 0W40. No baffles or accusump.

What's your summation of the data?

What initially drove me down this road were ENGINE BUILDERS pointing out the oil sump design vs my usage of the vehicle. Working backwards from there and seeing that hot oil will slosh as much as 60* up the oil pan given 1.3g of lateral load... it then just became a matter of finding some data to support the idea better. Saw oil pressure as low as ~20psi in autocross at 1.4-1.5g... You present the data so well and digestible. I can see it in my own logs and can vision laying things out as you have, but, to do what you do with your posts is something I just don't have the skillset or equipment to do. Thank you again for a great post and providing some harder data to analyze!

Another thing to consider is the actual oil level in the sump. 7qts seems like a lot until you watch a video like this:

They intentionally under-fill the sump to illustrate the point, but, it still stands that several qts of oil will be constantly flung up into the cylinder head... especially at 6,000rpm. I imagine the sump level would be at it's lowest as you blast down the straight at high rpm for extended time and then enter turn 1 which at most tracks is a heavily loaded brake and transition.