I'm probably opening a "can of worms" since this has been discussed plenty of times, but I have a new question. I've heard lots of ppl say they do the "run the crap out of it" break in and have had no problems. Others do what the builder says which is keep it easy for 500 miles, blah blah.

My friend has a built 306 fox body, did an easy break in. He agrees with the hard break in, but asks the question, "How long does the motor last?" Meaning, do you lose life off of the engine doing a hard break in vs an easy one. Is the hard breakin best only for race motors, or motors that plan to be rebuild each season or can they last 200,000 miles?

Now my other question is, am I doing a hard break in? I've been fighting with a power loss problem which turne dout to be a timing issue due to a wrong timing tab (thanks five7kid) and each test drive, I run it to 5500. This last test drive, I got the car sideways. Am I being too rough or what? Should I ease off? I still have much more testing/tuning to do. What do you think?

 

If teh initial break in was performed correctly (cam/lifter run-in if a flat tappet, ring seating runs with accel/decel at RPM), the subsequent 500 or so miles should be done rather gingerly to allow good cylinder polishing, main, rod, and cam bearing burnishing, and good oil flow under relatively light loads to keep all the loosened particles in the filter and not bypassing to the rest of the engine.

GM suggests this:

http://72.19.213.157/files/BreakIn.pdf

 

most engine builders, or racers run them hard and it seats the rings faster and better. most racers break in the cam roll it off the trailer and hit the 1/4mile. and i have seen alot of engines broke in this way and they are still running great a few years later. but either way works.