Break-in period: myth or fact?

The conventional wisdom endorsed by most, if not all, manufacturers is that for the first 500 or 1,000 miles a car should be driven gently, with no runs to the redline, and not at a constant speed (i.e. no cruise control). The reasoning: the rings need to properly seat, and any rough edges need to be smoothed off, before putting a great deal of stress on these moving parts.

However, at least a decade ago one of the car magazines quoted a Corvette engineer saying that no such break-in period was necessary because of the more precise assembly and much tighter tolerances in today’s engines. Also, if a break-in period is critical, then why are cars with virtually no miles available for test drives? Logically, dealers would break-in one or two examples of each model, and then use these as demos for all test drives.

So it seems likely that the widely espoused break-in period, while once valid, has survived based on tradition and the philosophy of better safe than sorry.”  If there has been any recent research that supports the need for a break-in period, I’d very much like to see it. But I doubt this research exists.