Not Ranked
I think the early MKII's used med riser heads, and the later MKII's had tunnel port heads, but with smaller valves ( ? 2.05's) to limit top end HP/RPM's to make the engines durable. They were not built for maximum power, but reliable power. I had always assumed the MKIV's had tunnel ports as well. After 1967, due to increasing speeds, there was a 5 liter limit placed on engine size, and therefore the GT40 MKI that won in 1968, '69 had a small bloick.
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"After jumping into an early lead, Miles pitted for no reason. He let the entire field go by before re-entering the race. The crowd was jumping up and down as he stunned the Chevrolet drivers by easily passing the entire field to finish second behind MacDonald's other team Cobra. The Corvette people were completely demoralized."
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