Bullsh*t. Youre offering advice that may work for some racing engines, but not for the family sedan.
Yes clearances are tighter these days, so you dont have to baby the car, just drive normal.
My last three cars Ive broken in have gotten 10% better mpg than the official rating, which is about 25% better than most folks get in real life.
Anyhow, I wouldnt trust BS from a young whippersnapper who totals cars by playing Andretti in the city over manufacturer specs--especially when I have years of experience showing that following the normal and recommended process works fine.
All youre going to do by running it hard is to waste gas and possibly total another car.
Another thing to consider are bearings, which also need to be run in, transmission, and suspension components. Breaking them in hard can shorten their lifespan considerably or even break them.
Hard run in-is indeed used with some high revving motorcycles and cars, but its plain stupid racer-boy mythology for regular cars.
Its not racer boy mythology. Running in softly will result in the rings never properly wearing into the cylinders when the initial cross hatching wears off - this only takes 15-20 minutes
The first few miles are therefore the most important as the cross hatching is there to do this for you - whether you run in hard or soft. This is all by the by for family cars as this is probably already done at the factory or at the dealers, so what you do is pretty pointless.
15 years of stripping, preparing and building both racing and consumer units has shown me this - not heresay. A lot of manufacturers handbooks dont even mention a runin period nowadays anyway! We run everything in on a dyno - 3 or 4 flat out top gear runs over the course of 10-15 minutes and thats all that needs do ne - you dont need to do anything else - EXCEPT CHANGE THE OIL !!!!
You dont need to run any bearings in the engine will already have been run by computer at the factory for about 100 simulated miles by nearly every manufacturer nowadays. You only need to run components such as bearings and camshafts when you have replaced them.
Suspension components and gearboxes dont need run in either - this is already done at the factory as well - unless were talking some of the scrap that comes from detroit - still using 1950s technology.