I had thought about putting this in the tech. area but as it is a 60 some years old article, I put it here.
This article from Cycle World :
Harley-Davidson Kr-Tt & Sprint Cr-Tt
https://magazine.cyc...tt-sprint-cr-tt
Lists the KRTT red-line at 9,500 rpm, with racers going well beyond that.
Now as they had no rocker-arms or push-rods, fewer things to go wrong, but it still amazes me that a flat-head racer, and this was not the ultimate KRTT, hit rpms several thousand rpm higher than factory small block auto racers hit for another six years or so..
A curious item; in another site where they spoke of taking the KR engine to Axtell for head work, in 1967, he took one of his engines , removed the Tillotsen, carbs., put on two Mikuni and got a 3hp increase.
After Axtel's work, they got 60 some HP, at the rear tire, out of the engine.
