Both the 165s and the 185s are great heads. But you are looking at it backwards. You build the engine to flow what you want it to flow, dyno it, determine the peak power rpm, and the shift accordingly. With either head on a street cam, the engine is going to be way past peak power at 6500rpms. These engines aren't like a 2jz with 3.0L of displacement, the 5.0L of displacement sucks a 220cfm intake port like a straw above 6000rpms. Building an engine to run good at high rpm is the absolute opposite of what you want for the street. That's drag car stuff, where you dump the clutch at 6000rpms, and the engine never goes below 5500rpms. The whole point of the AFR 165 is that it has great intake air velocity at low RPM that gives you gobs of torque down low, for fun on the street. That's what puts you back in the seat when you roll into it in 2nd gear at low speed. Don't worry about the RPM; focus on the overall performance. Shifting a 2 bolt 302 block at 6500rpms is risky enough. My 347cid engine with 192cc heads peaks at 5600rpms, and I shift at 6100rpms for perspective. If you stop focusing on the high rpm, you are going to end up with a much better engine.
Kurt
