Do what the factory says.
Engine breakin was mostly for piston ring seal and modern engines have very
round bores and rings. Many ( all ? ) engines are run in at the factory so
much of the break in has already occured.
Modern breakin is more about wearing in rocker arms,piston pins, camshafts
and the like.
Older engines or home rebuilds with a hand held hone need alternating 75%
throttle and coast but no high revs to break in. This is done so cylinder
pressure forces the rings outwards causing them to sand against the hone marks.
If
the engine is driven lightly or left to idle unloaded during a breakin, the
hone marks are burnshed off before the ring wears into the bore.
Ater a rebuild, my oval track 307 Olds motor sees 1500 RPM till it gets to
temp, a 2 mile on / off throttle drive down the country road then it is off to
the track. At the 1/2 track it sees alternating 75% throttle / closed throttle
then full throttle at the end of 10 laps. It is left to cool 45 min then
back out for a normal 10 lap session. A few checks for leaks and it is reaty
to
race.
Harold
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