For the Sarah Project motor, I have examined and analyzed eleven heads. I believe that I have determined certain things to watch out for, and things to verify.

Therefore, in my search for some good aluminum, I have come up with some things I want:

First: I want a head that is as flat as possible to start with...
...lengthwise;
...diagonally;
...laterally.

I want minimum brinelling.

I want minimum "sinking" between the combustion chambers.

I want minimum distortion around the headbolt holes.

I want minimum heat distortion of the aluminum around the combustion chambers.

In other words: I want a cylinder head that has not been cooked.

And...I want all four cylinders to have good clean spark plug threads...no cross-threaded or damaged threads. Thread-serts are a complicating factor that I would prefer to not have to deal with. On a NA motor, thread-serting one spark plug thread is not a problem.

But for a boosted motor, as I see it, if one cylinder has damaged spark plug threads, then all four should be 'serted...to maintain uniformity of spark plug heat transfer away from the spark plug in all cylinders. A boosted motor will place more heat load, and therefore more heat dissipation challenges, on the spark plugs and their threads in the head. Having one spark plug that has a different heat transferance path and rate, due to a steel insert, than the other spark plugs is not an operating parameter that I want in a boosted motor.

Some might consider that to be extreme. Too bad. Having one cylinder running with a spark plug that is running hotter than the others could lead to a preignition problem in that cylinder; or could lead to some serious misdiagnosis of operating conditions: as in "Why is number 2 cylinder running leaner than the other three? That number 2 plug looks like it isn't getting the fuel like the others." In actuality, number 2 is not running leaner than the others; it's just that number 2 was thread-serted, and the others weren't. And because of the threadsert, the plug can't get rid of the heat as fast; therefore it looks like the plug is running in a lean condition, but the actual cause of the different color is lack of heat dissipation. Very few people test for threadserts in an aluminum head when they are trying to diagnose running problems; they just look at plug color. And unless they have a problem unthreading or installing the spark plug, they never even think about it.

I do not want to have that problem; nor do I care to set it up for someone else to have that problem in the future. So for me it is either no threadserts, or all threadserts on a boosted motor. If I can have a choice: I'd rather have none.