Gearing.
The K2-K6 bikes got a 17T front sprocket and often a 102-link (sometimes 104) chain to move the rear wheel back a bit.
The winners around my shop's area in those days were using Conti tires because they had more rubber grip than Bridgestone, but less than an all-out drag tire.
Mostly Hooker headers were eek-ing out a tenth or so, but the top racers I knew had HM300 pipes sans baffles. I suspect he also had a K0 engine with 52T rear sprocket, 16T front, but in a K3 frame, running Action Fours 825cc kit in 1972 and their 836cc kit in 1973. I left the area in summer 1973, lost track after that. He said he had the 'stock cam', was in the low 12 second brackets, everything had to be street-legal (including turn signals, being Illinois...).