Originally Posted by Davezilla
So on the Diamond head the combustion chamber protrudes into the bore? that'll be nice since it can save time shaving the top of the jug down for sure. I'd use the copper gaskets from Juice to prevent gasket compression and get the squish clearance just above 1/4mm just to be sure the piston can't hit the head. the .016" thick gaskets he sells come out to about 0.4mm so by adding one of these at the base or at the head you'll end up with about a .65mm squish clearance which would put the compression ratio at a more reasonable level and prevent the piston from hitting after the engine warms up etc... As long as you keep the squish below 1mm you'll be in the acceptable range where it can still work to prevent detonation really well.
I know on my current running engine it has a 0.75mm squish clearance and the compression ratio came out to 12.7:1 so I run 93 octane premium and have no issues with detonation, of course, that's the static compression ratio and the actual is measured from the top of the exhaust port up making the effective compression ratio closer to around 8:1 or so.
Yes with the right gasket that is thinner than a stock kit thickness gasket the outer edge of the squish band will be slightly down into the cylinder bore, the head gasket actually seats around the squish band rather than the edge of the combustion chamber sitting on the head gasket like it does with all the other stock and after market heads.
Not only could this increasing compression on an engine that hasn't had any deck material removed but its also going to help prevent blowing a head gasket possibly, of course if the head gets loose none of this will matter since it will leak no matter what, but the way Jake had them design this head it actually sorta interlocks with/in the cylinder bore when a thinner .016 etc... gasket is used, this also puts the combustion chamber perfectly centered over the bore since the outer edge of the combustion chamber closely fits inside the cylinder bore just slightly.
I'm using a stock thickness head gasket with mine since thats what i have on hand, i shaved the deck height for use with this thicker gasket, the next engine I build with the Jake head design will likely get a thinner gasket, next engine to get this head used on it will be one of my dax GT5 type engines.
I'm not trying to start a debate over which head is best or anything like that, and really this is kinda the wrong place to talk to much about it, but I do like the design of the Diamond head even though its big and tall compared to all the others, I am gonna go down to my local motorcycle shop and see if I can find a longer reach NGK plug for them, the E3 3.22 will work,but even as long as it is it could stand to be 1/8-3/16" longer reach to use all the threads in the head.
Once I find out which plug is the ideal length I'll post it in the correct location so others who may be interested in running one of these heads will know what plug they need to get for it.