Because they have no time for a proper break in. And the customer doesn't want to pay for them to basically drive the car until fully broken in.

Ideally, a rough tune would be done, then the engine broken in (no boost!), and then the car would be properly tuned.

 

I was also wondering this. I have never owned a piston engine car but have worked on my fathers mustang and several hondas and was always told that its important to let a new engine feel its full range every now and then in order to make sure eveything settles right. i know rotary's are totally different but this same principal still seems sound. I am not trying to excuse my earlier ignorance, just asking.

 

Are you talking about a piston or a rotary?

Piston engines have to ben ran very hard in the first few hours after a freshly rebuilt engine has been put back in the car. This is because the rings have to be seated against the crosshatch to seal properly, since the crosshatch causes the wear pattern in the rings. Rotaries don't have any kind of crosshatch in the housing so therefore the break-in must be done much more gradually and easily for the seals to seat properly.

Piston engine rebuilds are a lot different than a rotary, like I just explained, so you can't really apply piston break-in characteristics to a rotary, they're completely different.

 

I was referring to rotary only. Thanks for the info.