Does anyone know why the 225 was spec'd with a deck height .140" in the hole? Seems like that would do all kinds of bad things: bad for flame travel, emissions, compression, power, etc. Looks like a very inefficient situation in a pretty efficient engine.

FWIW, I read a formula once (that I can't recall right now) that indicated raising the top ring in the bore by "x" would typically produce"y" increase in torque. As I recall, using that formula and going to a zero deck height would give about a 6 or 7% increase in torque, all other factors being equal. Of course, I don't know if that's true in the real world, but it made for interesting math.

It seems ironic that the 170 spec'd a .000" deck height.

The 170 SL6 was designed on a "clean sheet of paper", the 225 was an after thought which added 1 inch stroke to the 170, this is why the 225 has so much negative deck, that is needed to keep the compression at 8.4 with the 3.400 bore and the 54 cc head chamber. (both are 170 "carry-overs")

Your ideas to get a "better" 225 are good ones and racers do this by using the 198 connecting rod and a 2.2 Mopar 4 banger piston to make a "long rod" 225 with close to zero deck. (and lots of compression)
DD

Thanks, Doc. I figured it was something like that. I guess I'm still confused, though. The 225 has a 1.000" longer stroke than the 170, but also a 1.000" taller block, right? So, where did the .140" go? Admittedly, I'm assuming the 170 and the 225 share the same pistons; is that correct? If they have different pistons, I suppose that would answer my question. Either way, it all seems like a pretty crude way to limit compression on the bigger motor.