This might seem like a strange question but I am uncertain of the best oil to use in my professionally built small block. It's a 340 punched out to 417, balanced and blueprinted. Although I use the car as many weekends as I can (local cars shows), it only have 2500 miles on it in those fives years. THE oil has been changed three or four times, only once by me. I was going to use Mobil 1 10w-40 but the shop did not carry it (They has Mobil 1 5-30 for my turbocharged inline six?). In fact they only synthetic 10w-40 they had was Valvoline High Mileage Formula. The guy behind the counter said that was a good choice - it seemed like he was experienced and informed. So it's in the garage as a weekend project - but before I make the change - why not ask the experts? Maybe just use dino oil?