I understand those are purpose built race cars which makes sense and I have been running 5w30 wt oils for years now and see temps from the teens to 114+ and my bearings looked real good after my usual 5+ year teardowns/freshen ups. When I see guys recommend 20w50 because of wider(race)bearing clearances I cringe unless your cars sits in the sun at 100+ degrees before start ups............
Not that uncommon to race in 100* temps in the Phoenix / Tucson area. Pulled in to the track in Tucson a few years ago and it was 105 - in the evening!! Yes, 10 lbs per 1000 rpm is generally accepted as the standard. What is the general rule on viscosity change when switching from petroleum to synthetic? - all else being equal.
Depends on whose oil you start with, and whose oil you change to.
I'd never change oil without talking to the manufacturer of the oil.
You can buy a 40 that is almost a 50. What if you are running a 40 that barely makes a 40 and then you switch to an oil that is a 40 but is almost a 50?
There need to be more time spent learning about oil.
Testing oil is very costly. I have seen testing done in a sloppy manner, where a great oil made less HP than a cheap oil. It was piss poor testing.
