What is the difference between AAC and ABC sleeves? Which one makes more power and which one lasts longer? Ex. JP has the FX21-R02 which is AAC and the FX21-R03 which is ABC. They are exactly the same except for the sleeve.

Can someone answer that question? I'm curious as to which is better for what reason.

AAC is better, but irequired certain conditions and different desing then conventional.
Too much to write, just try to look this forum-there is an answer (exclusive nitro zone).

I'm curious... If AAC was better, why did the Kyosho team used the ABC Sirio in the last Pre-Worlds in Brazil? Would be interested to know as well as the a lot of feedback seems to indicate that the AAC sleeve Sirios are good race engines but unfortunately does not last long.

That ones simple. Sirio havent figured out how to make the AAC work properly without premature detonation of the engine when extracting maximum power.

As i sad before AAC is the best possible set up fr ou engines, but it is required sertain conditions and special handeling. Are you sure Keyosho team was using ABS and not something else. I got info that there was something different then ABC.
About AAc do not last long, if you look way back in one of my post way before Novas came up with their AAC engines, I was talking about + and - of AAC. The bigest problem with AAC is , that sleeve getting loose in crancase and during the microvibration create a lot of micro debry of AL, which goes to combustion chamber, light up and raise temperature tramendosly. So Detonation began, filament getting melted. People are thinking that clearance is too low, and start putting extra shims, lower temperature and loosing power. Ther eis way to temporary fix it, but it will be dead crancase and not too many people can afford it-I know for fatc that one of my AAC set was making very good results internationaly , but start getting loose, so racer just glued in crancase ( what a real solution) and problem has disappeared. I didn't tryed it my self, but I absolutly belive it happened like that. Only one thing is nes it is glued, no way you can take out out again. If do It I will use retaining compaund by Loctight #609 ( green).
Because of this I don't make AAC sets anymore, also I found that AAC s realy good at lower ambient temperature and for most ambient temperature is better BRB.
Other solution to use AAc on our aplication is design which we use on Palmaris PS12-it is AAc , but it doesn't have sleeve. So we don't have look for solution for debry and we have much better heat transfer rate then any conventional design (thre walls-AL-AIR-AL). We have only AL wall.
This expirience was gain back in 1980's and now AAC sets are using only on DIESEL engines ( no glow plug, they use some special chimical to lower detonation point with the same combustion speed etc).
BTW, life of p/s set dictate not by sleeve material, only by piston material and I am sure you see already that new Microcastg pistons don' last too long, I saw it already many many times.
I am done for now