Mini
From what I heard, Pontiac went out of their way to make sure the cars tested in magazines where NOT from the showroom, they would take them, install thinner head gaskets, adjustable rockers, more aggressive timing and a few other things, like a 421 or 428 in place of the 389, or 400( block looks exactly the same.)
Royal Pontiac sold a Kit to do all the above to your own car.
There was a big stink at Pontiac when one dealer let a non prepped car get tested.