Carbon fiber is rarely used as a single. It's always used with epoxy as a matrix to form a composite.
The carbon fiber - epoxy resin composite cannot be used on engine block, because carbon fiber is a directional material, that means when it's under impact, the composite can support huge strength when the force is parallel to the fiber direction, but support low when the force is perpendicular to the fiber direction. Therefore it's hard to design as an engine block and complicated in manufacture.
Aluminium magnesium alloy (metal is non-directional) is suitable for making engine block. Different material can block the dislocations moving of the material to increase the strength.
The carbon is used in gearbox to increase the wear resistance. The physical property for carbon and carbon fiber are different. The best design for using carbon fiber-epoxy composite is chassis or car shell of F1.
I dont know this ans can help you or not....