it is not recommended to use
synthetic to break in those engines.
there are breakin oils(some already mentioned) to handle this. i use
brad-penn products, this is the refinery that used to make the old
kendall green racing
oil. they have a breakin
oil (for initial start-up to
break in the camshaft) after that i would recommend the 20-50 they
offer. i have found the valvoline gets the consistancy of water after
about 100 miles, i have stopped using this. i cant comment on the shell
product i have no experience using it. i can say that the brad- penn
performes excellently for street and racing, i even have a hard time wiping
it off of surfaces, its quite sticky, the viscosity remains after heating and
punishment. i have 3 solid cam installs using this
oil and no failures.
http://www.bradpennracing.com/
Fred