706 vs. 317 Modified (Turbo) 5.3L
Though LS enthusiasts seem to think some sort of magic happens when you introduce boost pressure from a turbo, the reality is that things actually remain the same. The only change is usually that the differences experienced naturally aspirated occur at a higher power level. This was the case when we added boost from the same single-turbo system to both sets of cylinder heads. Run with the Precision turbo, ProCharger intercooler, and 317 heads (at 7 psi), the 5.3L produced 691 hp at 6,700 rpm and 612 lb-ft of torque at 5,000 rpm. After running the same setup with the 706 heads, the 5.3L produced 706 hp at 6,500 rpm and 641 lb-ft of torque at 5,000 rpm. The gains offered by the extra compression of the 706 heads remained (and even increased slightly) under boost.