There's something to be said for experimentation, looking for a challenge. Searching through catalogs and tech articles is a gearhead treasure hunt. Engine building/tuning can be a great place to flex those creative muscles. Try as I might, I cannot come up with a concise, overarching, explanation that will make most choices clear for most owner/builders out there. IMHO, it's that humungous gray area, and all of the possible combos lurking there, that keeps things interesting. Best I can offer is a list of a few of the extremes, which define certain boundaries, and the rationale behind some choices, primarily my own. How many members will fully understand, let alone agree, is debatable. IMHO, there are no "one-size-fits-all" answers. Beyond that, it's all varying shades of gray. For those of us with a number of bikes, building each one for a different purpose opens the door for a highly-specialized build...or several. It almost
demands that. Too many copies of the same thing gets boring.
I've been around, and part of, the gearhead world longer than most, which accounts for a goodly amount of my perspective...which has changed & evolved a lot over six decades. Everyone should have the same opportunity to go through the process and as they see fit to do. I've simply reached a point where serious riding is the top priority and other parameters...a.k.a.
the rest of the bike...need attention, to achieve balance. That's not for everyone.
IMHO, peak horsepower, top speed and up-front cost draw too much attention. I've experienced 80mph+, on a well-setup, CT70; it's not that enjoyable and, at this late date, no longer even boast-worthy...let alone practical. It's enough of a challenge balancing a rolling chassis for 60mph power (which is easily achieved, these days)...a topic about as glamorous, in text, as shopping for a new refrigerator...and not something you really want to live without. Aside from a closed course, 99% of the miles will be accumulated while traveling below 60mph.That doesn't invalidate any engines, or tuning combos. Even limiting the discussion to powerplants, those three headline numbers don't really tell you much. There's the qualitative side, mostly comprising the "how", rather than the "how much", it's what you'll be living with, as the rider. That's where engine discussions get meaty.
My money was on, I'm just gonna put the reliable stock Honda Nice head on and not have to worry about it.
A specific item on which I can comment, from firsthand experience. Jarred's motor will give up some top end horsepower, in favor of proven durability. Yet, it's almost a non-issue. The stock Nice head, with minimal...and I do mean
minimal...port cleanup can easily support 70mph power levels. I'd be more surprised if his 62mm-stroked Nice couldn't pull that, at the minimum. Torque will be unaffected so, the reduced hp will only move the needle a little bit downward on the seat-of-the-pants dyno. IOW, this thing will pull itself along with effortless ease well beyond 60mph, with a fat & flat torque curve...power across the entire rev range, without much of a peak. It'll almost ignore headwinds and modest grades...a torque-surfer's dream. All else the same, hp differences are due to the rpm at which the peak occurs and that kind of power difference registers more on the speedo dial than the s.o.t.p. dyno.
Funny (as in "peculiar", not "ha-ha") thing is that I see more similarities, than differences, between the Nice & TRX heads, including the laughably small valves and 5.0mm valve stems. My stock, daily rider, is going strong after 23,000 miles of vigorous use; I don't baby it, in the least. And it's not the first one I've seen reach this milestone. IMHO, the facts speak for themselves.
