HiI'm new to this site ,but have been reading tis for about month now , anyways what I was going to post is how different vis. affect engine performance . Since graduating as auto tech. and working back in europe for Fiat in their racing div. I do know thing or two about engine performancce . So I have hooked up vacuum/ boost gauge on my volvo 850 turbo , yesterday I chenged engine oil ,went from Chevron delo 400 5w40 gr III , to nascar synthetic 10W30gr IV and V blend and instantly gain 2inhg of vacuum which is pretty significant,. How good this oil is ? I have no idea but reduces friction inside the engine I'll keep ti in for 5k and change it , this is my plan , Eric