Need .21 buggy engine that is good at high altitudee
 

I was just given an old Kyosho MP777 and the OS VZ-B is really worn out and will not tune at all. I am looking for an engine that runs well at high altitude, I live at 8770ft. I know it's all about the tuning but it's also about how much air can be introduced therefore the bigger the venturi the better, at least that's what I am assuming. The VZ-B had a 7&8mm but most of the engines that I see now have a 6mm or 6.5mm.
I have been looking at Amain and have a short list of engines.
Protek Samurai RM edition
Protek Samurai R03
O.S. B2104 with pipe
O.S. .21 XZ-B VII
Any opinions??????

Just remove a headshim

Ultimate MXS, OS based, Tessmann 2. Great engine.

I am curious on this topic. I recall the first time I attended a race where the altitude was very high. I couldn't figure out why my engine was running so hot and had no power. Nobody could. This was back in the early days when I was still pretty new. I look back on that event and my buddies and I still discuss this.

I recall the solution was as already mentioned, alter the head clearance, or even run more nitro. Like 40%??

Ideally in high altitude what should be done??