quote:
FWIW - my motor (a 1971 455) was broken in with 14 full
throttle runs on the dyno using 10W30 oil (changed 3x). From that point on
my builder recommended that I run 10W40 or 15W50 synthetic to maintain good
constant oil pressure at all rpm as the motor was built with larger main
bearing clearances than factory 455's. These motors have very large main
bearings (3.25") which means a high bearing speed and lots of heat build
up. Most 455s never see the high side of 4000 rpm in passenger cars, once
you start to twist them for more power you have to keep the heat off the
bearings.
As a point of interest - when we changed to Mobil 1 15W50 for the last dyno
pull we lost 10 hp.