[glamcem]

also the reason why we see greater oil pressure is because the thicker oil cannot flow through all the areas in the engine as good as the thinner oil due to tighter tolerances, (lesser the general volume higher the total oil pressure), so oil pressure alone cannot be used as an indicator for better lubrication ...especially if the thinner (5w-30) already meets the ideal 10 psi per RPM at ~220F figures..

see below that I quoted from my friend's post from the Camaro forums:

I've been discussing this with many at the Miata forums (for my supercharged Miata that overheats despite having an additional air-to-oil cooler with Mobil1 0W-40), and also ended up reading the whole oil university section of Bobstheoilguy.com. In short, my attitude is now changed a bit regarding oil pressures at the track.

Long story short, it is the flow that is most important, not the pressure. When we do a cold startup, we see very high oil pressures not because the oil is everywhere in the oil, lubricating the engine beautifully, but on the contrary, because the oil is too thick to go through the oil lines (especially the small ones in the engine), and it is creating a massive back pressure, creating those oil pressures we see and running most of the oil through the oil pump's bypass line, not through the engine.

There is currently no oil in the market which is thin enough for a cold start - NONE. Thinner oils will obviously come to enough flow faster, so the engine wear, most of which happens at the cold starts, will be less. Now, the question becomes, what should we do for the track duty?

The goal viscosity is actually 10 cSt. This is the target viscosity for 30 grade oil at operating temp, 212 degrees F. Now, when we get to 302 degrees F, 30 weight oil becomes around 3 cSt, while the 40 weight oil will hit around 3.7-3.8. You might say that it is 20+% more viscosity, but it is still just 1 cSt; they are actually almost identical! The significance of 1 cSt does not become 10x as important just because you have a very low value in hand. Granted, the best oil would stay at 10 viscosity across the board, but there is no such oil at the moment.

Assuming we use same base as GM recommends, i.e. 5W-XX oils, should we use 40 or 30 for track? 5W-30 will have marginally lower viscosity at 302 degrees F, but it will actually reduce the friction, reduce the likeliness of oil bypass valve (which opens up at 50 PSI?), and you will hit lower overall temps. It depends on the engine, but higher grade oil usually ends up increasing the PSI without necessarily increasing the actual flow of the oil.

Bob's recommendation in this regard is to observe the oil pressure at different RPM levels. If you hit 10 PSI at 1000 RPM, 20 at 2000, ... 50 PSI at 5000 RPM, then you're good. If you see higher, then you should consider trying a lower weight oil. I believe oil pressure relief valve opens up at 50 PSI, so there is no point in testing above 50 PSI; it will be misleading with the bypass circulation added to the equation. Actually, just so you know, if you hit 50 PSI at as low as 3000 RPM, then you will start circulating more and more oil above those RPMs, so you're doing pretty poorly. If you see very low PSI at idle at the track right when the engine is very hot, it is not the end of the world. After all, the oil is flowing without any resistance at high temps, and the engine does not need much protection at low RPMs anyway.

I intend to try 5W-30 next time at the track. If a ZL1 with its supercharger can survive 24 hours of torture at the track with this oil, so can my car at a simple track day. What's more, 5W-30 used oil reports have never raised any concern, and I will have reduced temps and better flow of oil when it's needed most as the advantage. I highly recommend reading Bob's oil university chapters.