I don't want to be a wet blanket, but is there any answerable question here?
Just to be clear why I am saying this. The first round, many of us looked at the question as being "If you built the two engines with the same parts, what would the difference be?" In essence, an oversquare vs undersquare cid question. I think it's pretty clear that within a small variance, HP per cid stays about the same
If we now shift to the same question but add the largest logical valve we can for each bore, the rest of the build would change dramatically to still be optimized for engine, which then requires additional changes and cost (not talking only money, but cost on the curve too), depending on intent (same rpm range?, peak power only? peak torque in a certain RPM range?) Even Frank as a racer, would design a car for a specific RPM range and of course people on the forum often are building for an existing configuration of the rest of the car
Some thoughts of what would change that make comparable builds difficult to compare
- Intake port change - highly probable to keep port shape correct and take advantage of a valve size change
- Cam change - likely if we are going to keep in the same RPM range, but then you run into "big port small cam" or "small port big cam" comparison. This could be significant, think of TP vs CJ head, or think of high riser vs CJ head. The cam design is wholly different for those heads and a given cid
- Intake manifold - maybe change too, but depends on the head and what the new build was
- Chamber shape and size - likely with a bigger valve, to include valve spacing, which could actually hobble the big bore a little, especially if it can't make compression without a dome
- Compression change - likely with cam change (and could actually have to be lower for the big bore if trying to stay in the same RPM range)
There is no doubt there is some good thinking going on, but I don't know how you could compare those engines. A valve size change without any change to anything else doesn't change much if anything. Remember, the valve itself just gets out of the way, what you are trying to do when discussing shrouding is make room for a bigger seat and throat as that valve gets out of the way. Of course at low lift the valve is part of the equation, but if you don't optimize the rest of the port, as I said in an earlier post, you are just putting bigger lid on a trash can. It covers it, but the trash can (throat) is still the same size.
I post this only because I started playing in the sim and realized either the builds departed so far from each other, or to stay in the same RPM range, I had to pick cams and compression we wouldn't run in two comparable engines.
This discussion then turns into the old "stone soup" story, and the changes add up to a different build all together. If just going for peak power regardless of RPM range, then it's simple, big bore, big head, cam to peak, compression for cam and fuel, and the one with the best cylinder fill wins.
