I added a mountain performer head to my 2016 m8000. I will list the things i was warned or told about, then i will reply with my findings.
1. May not or will not actually cool, or larger cavities will cause hot spots from lack of circulation. Reply- i have shot the motor with a heat gun before and after while running hard at elevation, have not found a difference either way
2. Doesn't create more power, actually loses. This was pm'd to me from a fellow forum member who was performing dyno runs at or close to sea level. Reply, now i have not performed dyno runs, but i can say without doubt, i not only felt a remarkably better throttle response, it cleaned up and eliminated hesitation due to over-fueling in low to mid range. Also, i added 1.4 grams per cam of weight to clutching. To me, this means more power regardless of dyno. This statement can be backed up from a good friend of mine who is a doo rider. His response was wow, what a difference in the bottom end
People can say what they want, i like the "bolt on" head and would install again just to clean up the bottom end and throttle response as it did. Did it propel me to new heights or surpass my buddies by measurable amounts, nope. Is it worth it in gains to the price tag? Probably no, but thats for you to decide. For me, i like a clean performing motor that doesnt stumble or bog, which it helped my 800 there for sure