I sent my stock 243 heads off to a well known shop and had them do there magic, port, polish, valve job, and so on. I also went with thinner head gaskets per there instruction. I also added bigger injectors. I had 430/390 before and did 431/391 after the heads. Per the machine shop I needed 7.350 instead of the 7.4 push rods, so I swapped them out. The preload was now in limits so I retuned the car but it doesnt seem any faster. I can see from the data that the heads are flowing more air, they just aint making anymore hp. The dyno sheets look exactly them same like I didnt change anything. How can heads make zero hp. The well known shop claims the lowest thay have ever heard of or even seen is 20rwhp gain from there work. The said I should see 20-50rwhp gain. I have the car a little rich at 12.2 with 26deg of timing at wot.