On a rebuilt, we run it hard to sit the ring fast. On a new car that have
little break-in from the factory, you should try to break it in a bit. Drive
around like normal, but try to change the rpm. Do not let the rpm stay
constant, like cruising on the highway. The same could happens if you idle a
long time. Constant rpm set the piston rings and cylinder to wear at that rpm,
making them not as good they should be.

Robin Long wrote:

> Nowadays, with better engines and better built cars, is it still necessary
> to break in the engine? If yes, how?
>
> I have heard of some who recommend running at full open throttle on some
> load to "blueprint" the engine. How does this actually help "blueprint" the
> engine?