289 HiPo
Still breaking the engine in at 104.4 miles.
I understand that you should never use a
synthetic oil for breakin.
Using Twin Motorcraft FL1A's and currently Pennzoil 10W40. Going to switch at next change to Valvoline. My Stepfater who is a chemical engineer stated that it used to be (not sure if it's still true) that Pennzoil is "Parrafin" based and could cause the engine to gum over a period of years. Valvoline is (in his opinion) the purest production "standard" motor
oil.
I've had great luck in the past with Mobil 1 20W50 in my SHO.
