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You're right, making the connecting rods wouldn't increase the stroke length, but increasing the length between the crankshaft and the connecting rod will. That's what I meant I just said it wrong. The stroke should be twice that distance. I'm not sure what that's called though. 12V P-pumped Cummins have a CR of 17.5:1, a 4.02" bore and a 4.72" stroke. A VP-44 SO Cummins has a CR of 16.3:1. Since the bore is the same in both 5.9L engines, the stroke is obviously shorter. A 6.6L Duramax has a bore of 4.06" and a CR from 17.5:1 to 16.8:1 depending on the year models. The earlier Duramaxes have the 17.5:1 and a stroke of 3.9". The older powerstrokes (7.3L's) have a bore of 4.11" and stroke of 4.18". It's CR is 17.5:1. All of these engines are turbocharged.
The older, naturally aspirated engines (generally indirect injection) have the high compression ratios you speak of. The highest I've heard of is about 23:1... not much higher than that though. If you plan on having direct injection as well as some sort of forced induction, good luck keeping headgaskets on that thing without a CR lower than 18:1. Anything lower than 15:1 and good luck starting it on a cold morning.
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