This is an interesting thread and I've been a fan of motoman since back when I was into bikes. The first GSXR-750 I had was broken in the Motoman way and it was a missile. I completed the break-in for my new '02 WRX the Motoman way and it ran awesome throughout its life in the car. Broke it in on the drive home from the dealership and changed the oil after 42 miles. Even when I spun #4 rod bearing at 108K miles (oil starvation) upon tear-down the pistons were in great shape. New motor is in and was broken in "hard". Oil changes at 25, 300 and 600 miles so far.
The other thing about Motoman is he got me to critically think about engines and what is actually
going on inside them. Exchanging correspondence with him and Mike Shields really gave me sound direction.
So needless to say I'm a devotee of the so-called hard break-in method. I do also think there are some things people need to understand about their cars and engines.
The first thing is that new cars have their engines "run-in" at the factory. This takes less than one minute to do in practice and is much like the procedure detailed by mbtech in post #24. This or similar methods are a part of the QC of most every car off any automotive or motorcycle production line. The point is to ensure that the rings begin
to seal. It also pretty much guarantees that the break-in will not fail regardless of how the owner drives the car after that. This is not to be confused with complete break-in. The break-in is complete when ring wear has stopped. A failed break-in is when the rings have not seated and the bore no longer has sufficient surface roughness to wear in the rings.
I am confused about some of the break-in procedures put out by COBB and others though. No boost for 300 or 1,000 miles? Why? What magically changes in your new engine at 301 or 1,001 miles that allows you to run full boost and full throttle? Someone also mentioned that bearings "wear in". Huh? What!? The thing that wears bearings is metal-to-metal contact. If you have any metal-to-metal contact on your bearings then they are finished instantly. No two ways about it. Bearings don't wear in normal operation at all. Some have impossibly thin coatings that may come off over time but it's not from contact wear. I've got a bunch of new and used Subaru rod bearings laying around. I'll post pics of several for comparison.
OK, first stages of bearing death:
Unfortunately the this particular motor ate the bearing that actually spun. These are all "pre-spun". From left to right: Bearing is dead and all that's left is the copper layer, the last bearing #4 ate through to the steel and ground about .25 mm off the journal and disappeared.. Next bearing shows some slight eating into the copper layer. There is some babbitt layer scarring mostly caused by metal debris. The last bearing is not in so terrible shape but has definitely picked up some scars from metal debris.
This is what happens when your bearings "wear in"....
Next are four OEM bearings in very good shape:
From left to right: Brand new bearing with the coating rubbed off with a shop towel, 28,000 mile bearing from an STI (part out totaled car), Brand new STI rod bearing with zero miles, and 40,000 mile bearing from an EJ255 motor (totaled Legacy GT part out). The bearings look pretty much the same and the pics may not do complete justice. I did not mic the bearings however the babbitt layer on all bearings is fully intact and because it's only about .01 mm thin any wear into the copper would be apparent to the eye.
The point is that bearings don't wear and if they do something has gone wrong and the motor is dead...
I wonder if the guys at COBB break-in their race motors with no boost for 1,000 miles or whatever. I wonder if Subaru put-put the cars around for 1,000 miles before putting the test cars on the track at Tochigi or the Nurburgring...
The reality is that rings need gas pressure and vacuum (load) to seal properly in a new bore and there is only a short time available to do this before the bore roughness is worn down and can not abrade the rings in normal operation. With today's modern ring materials, such as plasma-moly, this happens very very quickly, basically within a few dozen miles if the engine is assembled correctly. That's why the hard break-in guys get it done straight away, no waiting and non reason to wait.
Doing it other ways will not necessarily cause the break-in to fail but the ring seal will not be as good as it would otherwise be. And sadly there are reports on NASIOC where builders suggested keeping the newly engine under 3K revs for 1,000 miles or some such nonsense. Needless to say the break-in was not successful and smoky oil-burning motors resulted.
Again with modern aftermarket ring technology break-in is going to happen easily and quickly even if you do not use a hard break-in procedure. However if you don't use the hard break-in then ring seal will not be as good as it could be and take a higher risk of having an engine that consumes oil significantly. By using the hard break-in the only risk you take is revealing poor assembly of the motor. Nothing about the engine changes in the first miles except the bore condition as no other parts on the engine are made or designed to "wear-in"