I know this is an old post, but I haven't been on the site in a LONG time haha....Looking over a lot of great topics by all you guys. After reading a lot about people's opinions on all the "Mopar" heads, I think a lot of you guys are underrating some of them. Seems a lot of people don't think highly of the 600-13 heads. But, I can tell you that our Valiant at about 2,600-2,700 pounds ran a 7.40 @ 187 m.p.h. with a naturally aspirated 622 with these heads. And that was without ever pushing it to it's max, this was with never once changing jets or timing and running it fat and trying to run a 7.60 index. The chassis is mild steel and not legal to go faster than 7.50. I will have to get back to you on any possible flow numbers, but obviously these have had a lot of work done to them, and the guy's that built the motor don't give Indy too much credit for any help at all.