Dumb question about motor rebuilds. On the older motors there was this run in period on mineral oil etc for about 1200 miles.
Then you could change to synthetic lubricants.
What's the deal on race engines?.
The following is:
JMHOYou still have to "run-in". For how long, depends on how exactingly the assembly is "blue-printed", how quickly the parts will wear, and how much "run-in" time is required to get the molecules "friendly" enough with each other . . . . . .
On engines I dyno test, 1/2 hour of run-in time at light load (15% to 25% of peak torque) is how I start. I then "evaluate" based on HOT leak-down % and dynamic blow-by in CFM. The acceptable amount for that value is based on the engine's displacement. If the leak-down is not within the value I'm looking for, I determine why, and take whatever steps are required to "FIX IT". Flat tappet cams REQUIRE a "run-in" procedure at lowered valve spring pressure, which is a whole separate issue. ALL pushrod valve trains need a run-in period, even roller cams. Do not ignore the need for this.
There is no point in "SPANKING IT", unless the engine is sealed up. BHP & TQ will be down.
All of this PRESUMES that the rest of the engine operating parameters, such as oil pressure, temperatures, LEAKS, etc, ARE WITHIN ACCEPTABLE SPECS/LIMITS.
One final note: Unresolved problems, even minor ones, can resolve themselves with sudden and EXPENSIVE noises . . . . . .
Once things are sealed up on "break-in lube", you can change to a synthetic based product.
Again,
JMHO Not all engine "professionals" agree on everything, AND, different parts can and do require differing procedures. Make DAM* sure you know what is required for your assembly.