Mike (MRieck): about that intake shaft: I LOVE what you've done with the place! I'd kiss those guides if I could reach 'em...Is that your chamber? And, how's the mixture tuning at 1/4 to 1/2 throttle, light load? Does it tend to gargle and then lean out? That's one of the things I know I'll face. I think maybe the K4 carbs will help with that situation, because of their mixing collars.
Jerry: if this works like I hope it will, we can do up one of those "F" heads you're scouting. It would be fun to see what the domed pistons and later cam would do with it.
About dimples: someone here said it best: it works well for lower RPM engines, and also for those that run very hot. Also, unless you've bored your 750 oversquare, there is one more dynamic to consider: cylinder swirl. The deeper-than-wider engine usually has more turbulence by default, especially when the pattern is guided by intake tract angles, like the 750. Going oversquare, as they say, "changes everything"...My favorite example of this is the 1000cc kits of the early 1970s for the CB: there were 80HP (big deal), 90 HP (that's better) and 100-125HP (ahh...) versions. The difference was in the heads, because all used the same pistons from Rocky Cycle, under private labels.
The ridged valves are, in one aspect, a production version of highly polished valves. This works because of laminar flow: the surface of the grooved valve sets up a thin bed of low-friction air, which smoothes the path for the air behind it to pass over while adding some shear mixing along the way. The valve is usally made thinner, but more expensive material is used for strength, then ridged and the seat pressures are lowered to prevent head loss. I've seen this on engines with solenoid-controlled valves and with torsion bar valve springs - also on Desmo Ducatis in the 1960s. I even saw it on a Harley 750 flattracker when he was torn down for suspected cheating. The ridges weren't illegal, but sure generated a lot of discussion, like here...these ridges also appear in high-viscosity transport piping, for similar reasons: low surface friction and drag, and reduced pipe wear in slurry situations.
The Hemi design, taken to its limit, allows for larger port areas, like big valves or lots of them. It allows (not in this case) the spark plug to be centered for the most even burn propagation. It also evenly distributes the forces of the expanding gases more evenly, which is where the extra torque appears. The little ridges in the 750 head, for example, mainly direct intake and exhaust flow, and were born of the CVCC (aka HCP) research toward more MPG and lower emissions. In that regard, they work well. But, they cause small disturbances, like ripples crossing a pond on the 2nd or 3rd trip across, that create "null points", or areas of lower force, during the burn. The most noticeable effect is reduced low-end torque and uneven throttle response.
So, I am going to mix "cylinder swirl" of the undersquare engine with the Hemi, provided I can get enough compression afterward, using the flat-topped pistons.
I fully expect to end up with an engine with no detectable "surge" at the higher RPMs, which is a characteristic of the "big four". I'd like to see the power come on sooner, stay longer, and more of it across the spread. More torque at lower RPM will be hard on the rods, so for now I'll stay with stock-ish bore sizes.
A bit of my "observed" history (not to be confused with official press releases):
The 750 engine was in development at the same time as the 1300cc CVCC 2-chamber engine, and some of its swirly design came, I believe, from that relationship. The CVCC was the ultimate forced-swirl design: a tiny little "precombustion" chamber with a tiny intake valve sat on top of the regular chamber. A small passage connected the two, and the 2-bbl carb had one side set to 12:1 A/F ratio, the other side at 17:1 A/F ratio. Two distributors fired 8 plugs on the 12-valve 4-cylinder like this: the pre-combustion chamber fired first (45 degrees early ! ), driving a rich whirlwind down into the main chamber (at an angle) to swirl that upcoming charge really fast. Then, the second spark (more normal advance rates) would fire the richer mixture at the outer edges of this little storm, which would then burn the leaner part for a longer push time on the piston. It was a peaky engine, so much so that many thought it had a radical cam, but that timing was close to our 750s. The result was an engine that would turn almost 9000 RPM in a car, getting 50 MPG at 80 MPH speeds, and would fit 2 Japanese or 2/3 of an American driver. It also made less than half of the emissions of a standard engine, but with no smog controls of any kind! We used to call them the "roller skate" cars, they were so small, but quick.
