[Jay S]

Originally Posted by steve25

The one thing I don’t like that was done in that video is that the bore length of his flow bench adapter was real short .

I agree. I watched the video, it was interesting. I don’t think that narrow tape for a smaller bore translates to very good data. The knotch combined with the short tape is pretty strange data to. There is something to be learned from it, but the lesson might have more to do with turbulence than bore size.

I build some LA mopars, and have a 71 340 duster. A few years ago Nick’s garage did a 390 CID based 318 stroker that made 406Hp thru A body exhaust manifolds like my 340 Duster. It had ported iron heads with 2.02s and a HFT, similar to my 340. But my 340 is closer to 380HP thru manifolds, might be able to split the difference with a cam like the 318 stroker used, it definitely had a better cam. But overall it appeared the extra stroke and cubes were more important than the bore.

[RocktimusPryme]

Originally Posted by Jay S

But overall it appeared the extra stroke and cubes were more important than the bore.

I think thats probably going to hold true in all but extreme examples. As long as you have a reasonable valve size, adding more CI is going to have a larger impact on power, than adding more valve size without adding CI. Of course if you can it would always be better to add both.

When you are CI limited, bigger valve will make more power. Assuming supporting modifications of course. The DZ and Boss 302 from the Trans AM Series come to mind. The Ford motor flat out made more power because its heads had a 2.23 intake valve compared to the Chevy 2.02. They should have won more of those races, but the Ford's couldnt stay on the track. Jokes write themselves. I also think Ive read that a wedge head motor is a more efficient design than a hemispherical chamber, but the HEMI simply allows you to shove larger valves in it, which on the dyno or at the top end of the race track is going to make bigger numbers. Engine masters did something like that with a Hemi and a wedge mopar, where the HEMI would have won a drag race but lost everywhere else.

Im sure if you graphed a static CI engine with different valve sizes and a static valve size with varying CI there would likely be an equilibrium somewhere.