There is no real flow differences between the 261 head and the 848 head. There were two versions of the 261 head, one was 86.2 cc and the other was a little larger. The 86.2 cc head is the same as the 5913 head in terms of chamber volume. the 848 head is 79.1 cc so it brings just a bit more compression.
As for the GM reported net, keep in mind that when GM did those evaluations, they did them under absolutely optimum conditions designed to drag out every bit of HP and torque so that they could advertise that figure. No accessories, no water pump, belts. So who knows what a real full dress production 261 would do. In fact, it would not surprise me to see a bone stock 261 dyno out on a modern dyno at or under 100 HP. Frankly, I think the carb was your limiting factor.
Last edited by Dragsix; 10/19/2023 4:39 PM.
