my results after a retune did not show a HP gain at the top end, but very fine low end HP and Torque gains. Given the near instant max/flat torque curve I couldn't be happier. For instance, at 2,600 rpm, I was at 170 ft lbs before tweaked/tuned, and 298 ft lbs after installing the tweaked manifolds. Note though, that tweak manifolds were my last mod, so these results are based on having already done the obvious mods to increase top end air flow. The result was VERY evident in traffic. Felt like an electric car w/instant torque.