Originally posted by trashcar
AAC will not run at or take the overtemp abuse that an ABC engine can tolerate. At the correct operating temp for an AAC engine it will out perform an ABC engine due to the like expansion rates of all components. They do not tolerate high temps as it weakens the sleeve. Sirio is an exception as is Palmaris as I believe both are parent bore motors.
Palmaris have BRB p/s, and have nothing in common with Sirios
Sirios are ABC only now, Collaris are AAC, both are made by Star Motors with Collaris made with their specs, like Nova based engines made by Novarossi.
Don't know of any other engine with AAC, so how do you say AAC sleeves weakens . My experience with early AAC Sirios and now with AAC Collaris ,is that they take more high reving high temp abuse than ABC.
AAC has better heat disipation properties than ABC, plus the better expansion rates.
AFM