Inliners International Forums General Discussion Hi Performance Flow bench day for the 848 head

Just a guess: 300 hp is extrapolating from the common "2 HP per CFM of intake flow" used for a V8 (and suggested by some flow bench manufacturers), which gives .25 HP per CFM per cylinder or 1.50 HP per CFM for an L6, and in this case 300.
I think it's a bit optimistic since (as said) the RPM is limited by both the stroke length and the inherent design (the port flow rate has been established, but sonic wave tuning isn't practical for siamese ports), but especially by the difficulty in increasing compression using only conventional techniques and commercially available parts.
I would use 1.4, or even slightly less, as a prediction depending on how well developed the engine is. The carburetor area in particular must be fairly large, pulling perhaps as little as 1.0" Hg. A 235 @ 6,000 RPM could use 500 CFM.