my trans am as the buick 455 fitted but i posted the pontiac one they do the buick as well. my engine is a 500hp + .i have an alloy rad twin kenlow electric fan and a high flow short neck water pump. do you know what pulley kit i need as i dont know what underdrive means. my trans am his a fast road/street car i am not using it for racing. i really need help as i dont want to put the rusty metal ones back. thanks kev