If we were to extrapolate the results to automotive engines,
many have paid much, much more for a 10 HP gain
That's roughly a 16% increase.
In the sense of scale, on a 300 HP engine, that would equate to around 48 extra HP
Not bad at all for a one or two phase (polish & port?) engine campaign
If you want extreme, I believe cams and a turbo would be indicated
( see also - what I'd do when I win Powerball
- the sleeper Trumpet!)
