Truly breaking in a modern engine takes more than a few gallons of gas so I really doubt many break in any engine on a test stand. One might start and work the bugs out on a test stand before mounting it in an airframe but unless you are into hours and hours of running it on a test stand the engine is not broken in when you mount it in the airframe.

Buy a high performance after market motor or have yours rebuilt with performance in mind and the good performance suppliers will set up test and run your engine first on a dyno before you take possession of it.

When you put it in the vehicle you expect to achieve the same performance specs the manufacturer gave you. If not then you suspect there may be a problem with your installation.

How many of the gas motors are tested and run at the factory. I wonder if they used an airframe or test stand.

A few tanks on a test stand isn’t breaking in its tweaking the engine and if you feel you want to do this on a test stand or in an airframe its personal preference and neither is going to hurt the engine.

If you use a method that you are comfortable with and it works for you then familiarity and confidence goes a long way to guarantee success.

Dennis