What's up, so it's time to change the oil in my GT. It's HCI bigger throttle body rockers and Pushrods with gt40 heads. For some odd reason he used 20w 50 racing oil in it for a recent oil change (before I bought it). Unless he's trying to hide unwanted noise (witch I fear). Should I go ahead and use 10w 30 or stick with w20 50 instead?