first 500 miles on my Roush 402SR i used Penzoil 10W30 as Roush recommended. First
oil change used Valvoline VR1 20W50. Warm idle pressures went from 30 to 40. Temperature with both viscosities were the same (never gets over 95c when idle traffic). I will switch to 10W30 or 10W40 in prep for my winter storage so I can start the car once a month.