Originally Posted by RallyBob
Yes, you have to be careful when you get to extreme CIH piston designs. There's a point where you just can't go any further with valve reliefs/raised rings/long rods. What happens is the intake valve reliefs will literally cut into the top ring land if the ring stack is too high, and if the piston crowns are made thicker to allow for the deeper valve reliefs and a long rod is used, there is the potential for the rod itself to hit the underside of the piston.
So in order to circumvent these issues you have to move the ring stack down a bit and use thinner rings, possibly use piston pin buttons with an oil rail support and also use rods with a smaller pin end (say .826") and an equally thinner profile rod to allow for all these extra clearances.
I will say that it is theoretically possible to stick a 6.2" rod into a 1.9, but you're so on the ragged edge this way, it's best to keep the rod to around 5.7-5.8". With bigger stroke engines, you're relegated to shorter rods...maybe 5.4-5.45" at best...unless you do the diesel 'tall deck' block.
Bob
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yes I had this valve notch/ring groove issue when I asked this set of custom pistons to JE,
I had to reduce a tad the notch deepth & diameter to be on the safe side.
IMO it's a pity the Total Seal pack is so tall,
if I could use Wossner rings instead this would allow for cd26mm without the need for a oil ring rail...
maybe it's time for me to consider pin button or 2 rings setup,
Bob do you think it's worth trying for my next 2.5?
rod ratio will not be better than 1.60-1.65 in any case.
Hiro