How long do leave break-in oil in a new engine?

I know racers that run break oil all season long.

That said, I have dumped the break in oil once dyno’d and I have keep it in for 25-30 passes which is my typical oil change interval. I’ve also ran engines that were not dyno, with Mobil 1 synthetic from day 1.

Do what your engine builder says and if that’s you, flip a coin and go with it.

I drain the oil I start the motor on after cam break in, change the filter and put the oil I want to run in.

I run the oil that I intend to run in it, when it's new. Engines don't wear in, they wear out.

10-25 runs

I have done my own stuff for a long time and can say this, using specific break in oil vs not doesn't seam to make a difference that I have noticed on the time slips or crank case vacuum. I will say this though, during the first start up after a freshen up or new motor, once it's up to operating temp, load the motor! This is what seats the rings. If you let it idle too much it can negatively effect the ring seat in process.

Unless your building a comp or PS motor and looking for every single HP, which BTW is way more involved with just break in oil, for us bracket folks, it's not a make or break deal.

Oil is cheap. I’d never make any power on the first oil fill, after the Eng has been apart. Put 2-3 good heat cycles on it and dump it and the filter. After that, run your normal oil at your normal interval