Good question. It really depends on if #1 if my numbers are correct. A cool head would be a nice addition. It may or may not require a special dome. For discussion sake, lets say the piston is different from stock or stock replacement. "H" has the volume at TDC (Top Dead Center) with stock cut head. Then we would need some additional numbers. We need to look at the piston crown angles verses the head squish angles, area,
Engine timing and rpm. Bore and port closure also is factored in. You can see where the port timing play into this. No need to set your head design around the wrong rpm. Why run it higher in rpm than the port can support. If you do it will make noise but run slower. It will also make you head design ineffective.
I have adjusted the piston dome volume to match what "H" measured and it did lower the CCR ( corrected compression ratio) If you install the larger cc cool head it will lower it further (CCR). It would also slow down the msv. Here is where it gets touchy as far as what to do. There is trade off's to be considered and it really depends on your ridding style and components.
Please do not take this wrong as its only for discussion. If you build a race
motor ((
Internal Combustion Engine ? )) and operate it like a play motor (( Internal Combustion Engine ? )) it will only go south on you. Basically there less forgiving. With a high performance Engine you have to be on top of it all the time, you get lazy and rut ru. Usually the builder set the design around a discussion with the owner. Couple of reason for this as the builder does not want the owner coming back on them and they also want the owner to get what they pay for. If the owner say I can operate it at the higher level then so it will be built with less safeguards. If the owner uses the wrong fuel or old fuel etc and blow it up it hard to blame the builder. Then one will de-tune it to operate with the limits of the owner. This happens more than one thinks. I personally know shops that will change the gasket thickness as they over bore with telling the owner. I have seen them look at the damage and make an assessment on how the owner runs the machine and make adjustment without saying a word just so it does not come back.
Time for a short story, I built a small block a few years ago and the owner which was a friend of a friend drove away happy. However not for long as it came back. Yep smoked it and blamed me. I fixed it however this time changed a few things. What I found out he did was after running it a few times he had a buddy that said if you advance the timing it will pull harder off the bottom. Need I say more, for some reason the owner failed to mention that. It did pull harder for a couple of runs then the pre igniton and detonation tore it up in short order. These was no knock sensor on that Engine. You can see how a lot of time no one will give you a solid answer. Live and learn type thing.
Back to your head. "H" would make the final call and I do mind throwing out numbers as long as one considers that there only a guess. I also base the numbers off of what I do and what is supplied even then it still a guess.
Based on the area numbers for rpm and the CCR I would look at a lower squish area ratio with an increase in angle. This will reduce peak torgue a touch however run stronger on top. Th MJ will be under square when compared to the MS and change the degrres BTDC. The degrees at which max MSV is at related to the Engine timming at full retard is important.
You can simply make a 1 to 2 degree change and make all the difference. One need to look at the pistons position when spark ignition occurs and the lag time of the flame front (flame speed). See how fuel works over gas. If your msv in degrees is to advanced the retard in flame front via the flame kernel/fuel can help correct. You can also see where (T) plays into this. As the Engine speed up in (T) it will effect combustion and related combustion events.
I suggest one goes to any online calculator and run the compression numbers based on what "H" provided. Then make adjustments to get the CCR where you would want it to run at a given rpm then enter in this data to a head program.
He has given bore, EXC, and total volume at TDC (Top Dead Center). The rod is 144 mm. When you do this make sure to note the base and head gasket information. When looking at squish clearance consider the head gasket squished thickness and the yet to be a documented deck. Since we do know hat number yet use zero as "H" noted with the proper base gasket/spacer in place the piston is now below deck. The EXC and deck to port opening number was taken with the piston below deck so your margin of error is less.
Also remember this is with out the new piston in it (I do believe), final numbers are based off of the final assembly. Change the piston type,etc change the numbers.
Kinda sounds likes I 'm passing the buck, don't it. I'm not just trying to help others have an understanding of the numbers. Just because it worked on one Engine does not mean it will work on yours. I got some piston to show that.
What I come up with as far as CCR is 7.0524, Based on what I see so far I would looking at 1mm squish clearance,45% squish,4 Degrees with a CCR @ 6.8 for starters. I based this off I have read and calculated for a dune Engine (non drag race).
Parts. Rev pipe, large Carb, Low primary CR, Multiple angle, large tip area ratio, low reed lift valve, Light clutch/rotating assembly and heavy rear tire load.
Keep in mind its just a guess from a Back Yard Hacker.