i posted a link or your thread about the 6.0. they made 480hp with the stock(iron i believe too!) 317 heads, then swapped to the L92 head and it made 551hp. but if you look at the comparison, under 5k rpms the 317s made more power and torque but died off at 5k. with the L92s, they stayed below the 317s, but when the 317s died off the L92 were really starting to shine. they ran the L92s up to 6500, and that 1500 rpm increase yielded an additional 71 hp