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This was told to my father by an SAE engineer.
The best break in, is; run the engine at high rich idle for 20-30 min. Then run it in high gear for 1000 to 3000 rpm bursts, remenber to put in high gear and at WOT run it from 1000 to 3000 rpms, then decrease till 1000 rpm reapeat again for 10 to 15 times then after this run it the same way but in low gear (2nd or 3rd) and do the same from 3000 to redline. After that is done you can do whatever you want with it. It's pretty easy but it takes a lot of gas :D to do it.
Paul
I'll come out there and break it in for you! Actually, when I build an engine I give it about 10 minutes before I let her loose. With todays parts there is no reason to wait even 10 miles before using the engine. My engines hold up nicely. I rebuilt my Pinto engine with a reconditioned head and immediately took it on a 1,000 mile trip to Washington from California including flooring it as often as I can (had to floor it over the mountains) and the crank had bearings that I replaced several years ago and the crank journals were all at tolerance back then...and I immediately drove it as hard as I could back then too. I've put another like 10,000 miles on the engine since then and have had no problems. So, my opinion is that new bearings with a new crank are not something that needs to be tip toed around with.
IMHO, break-ins are for professionally built engines so that if they didn't get something right then it will take longer for you to find out, and thus it might not break until after warranty has expired.
Keep in mind that Professional NHRA engines get a break-in of about 1 minute before putting out about 3,000HP.