The issue as I understand it is a harmonic that comes into play just over 6K. The engine would hit a wall power-wise. This was a struggle to "beat" in a race-only build I was party to. The engine was a Chevy stovebolt. Fixes included aluminum rods, severe lightening of the crank (really cut down counterweights), and high quality balancing of the assembly. That allowed the engine to pull cleanly to 7K. It's been many years but with methanol and single turbo it was running in the low 9s in a Studebaker.

Well, art is art, isn't it? Still, on the other hand, water is water! And east is east and west is west and if you take cranberries and stew them like applesauce they taste much more like prunes than rhubarb does. Now, uh... Now you tell me what you know.