706 vs. 317 Modified (NA) 5.3L
Right off the bat, it is obvious that the stock 5.3L 706 heads easily outperformed the 6.0L 317s. This was even more impressive when you consider the fact that the 317 heads offered more flow, larger ports, and larger intake valves. Credit the difference in chamber size for the majority of the gains, as the 706 heads were a full 10 cc smaller than the 317s. Tested on the naturally aspirated 5.3L, the result was an extra 20 hp, and almost as much torque. Equipped with the 706 heads, the 5.3L produced 468 hp and 413 lb-ft of torque. After installation of the
317 heads, the power numbers dropped to 448 hp and 398 lb-ft of torque. The question now, how would they compare under boost?