A STOCK vortec head has very impressive low and mid lift flow numbers. Not so much on the high lift numbers. I could be wrong - please correct me if I am - but I was thinking these heads top out on flow at about .550" lift. Great street heads,but if you are looking for a 6-7000 rpm head I would probably shop for something with a bigger runner. Remember,these heads were designed for stock performance,reliability and trucks. They are awesome heads,but not full on race material. Of course if I owned a set I would definitely run them. Anybody know any definite lift/flow numbers on these cast iron wonders?