high altitude heads?

[MAPEX]

Hi Guys,

I was recently reading an article that was discussing high altitude heads for vintage sleds. I'm not sure if I'm the only one but I'm not to sure what exactly high altitude means in regards to design or difference between that and a"normal" head. Any help would be greatly appreciated so I can stop scratching my head feeling like a dumba$$ who doens't know what he's talkin about. Thanks

Mike

[Joe]

Higher compression.

They ping at lower elevations.