Originally Posted by sr20hardbody
i wonder if it would be worth it to ditch the .5mm thick top copper ring and get an o ring groove milled instead?!
the real euro's use this set up with proper sealing just wondering this would also bring the squish down or maybe you can do both.
You are correct in the fact that the real euros use this but the problem is that the metal seals it, not the o-ring. On a euro engine, the o-ring is used to seal coolant passages, not combustion gas. If combustion heat gets to the o-ring....its cooked. The copper does the job just nicely and can take much more heat loading than any o-ring. Milling the jug to get the dome lower to get the squish right is very easy, requires no special extra parts, is very proven in practice and lasts a long time.
One way that running it without the copper ring may be better is aiding heat transfer from head to jug. It would keep head temperature down by increasing overall temperature of the engine. While copper is an excellent conductor of heat, it is still another medium in which heat transfers and has some resistance to transfer. It may be beneficial actually to keep the temperature of the jug cooler than the head, so piston heat transfer to the cylinder is kept at a good rate and that would likely help keep the piston crown temperature in check......thus keeping it from seizing. The heat sink on the head is pretty sizable so I doubt it will get too much hotter.
FYI, that last paragraph is mostly conjecture and has not been tested really.