Just swapped out the stock iron manif for Merc 496 alum manif on my 454, Chaparral 2550 sx. Picked up 2 mph on the top end, better holeshot and mid range punch. Next I'm going to take out the turbolators between the riser and manifold and see if that makes a difference. Then its on to the carb upgrade. Current carb is orig from the 330hp, so probably running lean.