The 1.22 would probably be the way to go. Then get the block square decked. From what I've seen The deck on a Dart block are all over the place (if that's what you are using) and need .005+ to get them squared up anyhow.

For sure!

Well Mike after much consideration and having a good conversation with Jim valako today I am going with your advice on this one. Jim was pretty skeptacle on anything over 4.250 also. His 565 that he runs extremely hard has the 4.250 crank, 6.385 rods with appropriate Pistons with no issues. After mocking one up we found a portion of the piston pin actually going below the hole.
(Not good) although I know there's probably several out there.
Our only thought was if we went with the 4.250 crank and 6.535 rod which I would think would keep the pin up in the hole even further yet. Jim just said he wouldn't recommend only because he hasn't done any testing with such and hated to suggest it not knowing for sure the long jevity of and or if there are any known problems. So in a nutshell unless that is a proven package then I wouldn't consider that. The good thing about what Jim is running is I know him very well first hand and he runs his boart extremely hard with no issues so is it worth trying to reinvent the wheel so to speak. When something is proven why change.

I don't mind taking some risk but if the risk out weigh the rewards then what's the point.


Any thoughts on the above?
Tks
John.

running a 4.375 crank in a 9.8 deck is far from re-inventing the wheel. As a matter of fact guys have been doing it successfully for a long time. It's obvious that someone worried about the pin coming out of the hole has no experience with building large cubic inch motors. What happens when we really pull the pin out and the oil ring comes out of the bore?

If you're going with a 4.25 stroke in a 9.8 deck block, why not go with the industry standard 6.385 Rod, with an off the shelf piston? That combo has been done a million times in everything from a 489/496, to 540-565ci.

The "reinventing the wheel" was kind of a figure of speech. Never said the pine would fall out the hole rather just meaning a portion of would drop below at the bottom of the stroke. The guy I spoke with Jim valako (valako race heads) had no doubt it's been done successfully however just didn't recommend it. He's no newbie at this and is over 900 hp with his 565 NA engine running pump gas.

I may still end up with 4.375 who knows but would like to decide relatively soon. I may build one of each. I doubt my boat will run in circles. Lol

Read my first paragraph. The other was just thinking out load.

jim is a smart guy and gave you good advice imo.the gain from .125 xtra stroke is not going to make epic power.as already mentioned if you go with the proven 4.250 stroke with the short deck block you can do so with off the shelf parts.if you are trying to squeeze all the power possible from a short deck by all means put that 4.375 crank in it.anyone care to guess the power difference in these 2 combinations?

Going with a NA I'm going to be selling it I took it on trade. For my 598. Call me some time 799-6187

LOL, I have this conversation every month with Jim. I know, like you said, he doesn't build them so he wouldn't give you his recommendation. He has built so many 540-565's over the years that it is just a good go to engine for him. Shelf parts, reasonably inexpensive, and he will stand behind them. Also, as stated earlier the 0.125" isn't going to be a game changer.

And yes, his 565 gets run extremely hard. I've run that thing for a few miles with the stick to the wood. (Dang LH throttle!)