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.
