Great thread, brings back memories of my (dating myself) 1987 Buick Regal Grand National. A good friend drove with me to my house and then he drove me to the dealer. So as a "reward" for his help I let him drive the GN home, with uhmmmm no restrictions. So we are making a left turn off the eway and he lights em up. Next thing I know my new car is sideways in a cloud of white smoke on the over pass.
But this was a car I actually got to follow down the line. Final assembly was in Pontiac and I worked at Truck and Bus in Pontiac. So I was able to track down build numbers, etc. and get in the plant to follow it down the line. I can tell you I was amazed that every car they took off the line got a "nice break-in burnout". And the real funny thing is I've seen them do that in the Heavy Duty Truck plant way back when GM made those. That's a show!!!!
I've always been under the "break it in like you intend to drive it" mindset. Nothing behind that other than the manufacturing tolerances and processes are so good there is no described break in that I know of anymore.
Which brings back another fond memory of my 1995 Kawasaki ZX-6 which did have a prescribed break in. 4,000 RPM for the first 600 miles and 6,000 RPM for the next 600 miles. I spent two weekends on the highway just going something stupid like 52 mph to get it broke in. HA!
There. Done with nostalgia Sunday.