So after doing lots of reading and doing my best to work my way through what I found, I wanted to get the input of people on here to see if I am on the right track. I have found it a bit daunting and difficult to work out what is correct in regard to 2-stroke tuning, as a result I have tried to research as much as possible on one part at time. What I would like to explore with people is the finer details of the 2-piece heads and also the quench zones / squish.
To make it easier to read I have broken it up into sections, if any disagrees or has anything to add to any of this then please do so, I have a lot to learn still.
1- Issues with existing 2-piece head / barrel kits:
I have been advised previously (thanks CAM2) that using a 2-piece head has it's downsides such as it's ability to seal properly due to the different expansion rates of metals.
Are there other downsides? Can the sealing issue be overcome with doing some lapping like in Mexicano's thread?
Link:A "Racing Engine" Built
Or something else like more head cooling? Just how much leakage is there anyway?
2- Dome profiles / quench zones:
So on the dome insert for the head I have here it has a simple taper machined into it at 15.5 degrees instead of something that matches the piston shape. I think this flawed because that's a shallower angle than the edge of the piston. I believe this means that a ring of the combustion gasses will be trapped between the angle of the head dome and the outer part of the piston curve at TDC. If so this could cause wasted combustion gasses, unburnt mixtures and also possibly promote both detonation.
Of all the times people have stated the squish distance they must be talking about the narrowest point then?
I see 2 ways for me to improve this, one is make an elaborate radii cutting fixture for my lathe to make the head dome match the piston, this would also let me machine the surfaces of my pistons to an exact shape and it would likely be a useful tool to have on hand for other projects. It could also potentially work wonders for me cutting my own combustion chamber pockets and therefore let me alter the quench zone to chamber opening ratio.
The second option is quick and easy- I read that unlike 4 stroke engines it helps to have some angle between the piston and the head in a 2-stoke, as in like the squish area making a wedge shape. I am at a total loss as to why this is though as it shouldn't be able to properly quench the mixture being like that. If this is correct then although crude just changing the angle of the head dome leading to the chamber to around 20 degrees would then move the narrowest point of the squish to the edge of the piston. From this narrow edge it would gradually increase in the squish height as it gets closer to the chamber.
3- Spark plugs:
The original barrels use a M14 size spark plug and the "upgrade" 2-piece kits I have seen use an M10 instead. Given there was an option and comparing the same heat ranges and so on is there any advantage to using either of the two sizes? I am guessing not but happy to be told otherwise.
4- Offset Chamber design (See attached pic):
This is when the combustion chamber is offset towards the intake. This is to help equalise the temperatures of the head and piston because the gasses are normally prone to heat up one side more due to them heading towards the exhaust port. It has been covered to some degree here:
Link: Cag heads and compression ratio
Any reasonable merit to this? or just small improvements to be had? I should have enough ability to make my own offset dome, if I succeed or not it would be a good mental exercise either way.
5- Dome to head heat transfer:
Another thing I noticed is that there the main part of the 2-piece heads only touch the dome on it's top outer edges. This is the only place where the head dome can transmit heat to the main part of the head. Is this done to put as much pressure on the top edge of the bore to help it seal or something? For me I would of thought it would be better to have a larger surface area between the two and then use some thermal paste.
Anything else I missed that could be improved? Lets say that manually making a custom head and dome isn't out of the question then what could be made even better? For example I could possibly make a head with a heap more surface area in it's cooling fins, I don't know if this would help for that much though.
That's it for now, sorry for the long post people