If I were to race an rb/b motor it would be a 383. It is by far the best big block from the factory even though it is the smallest and you give up a lot of cubic inches and torque compared to a bigger big block. with good machine work and heads/cam/intake combo it will really scream. it has a great rod ratio and you can really spin them up high, but thats just me, 99% of the guys on here will tell you to build a stroker and shift at 5500 rpm...