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Tech Question
Scott Marshall, Wills Point, TX, 1971 Dodge Dart Swinger 225
I recently purchased a 340 block and crank, the date code on the block is 7/10/69. I checked bore of block and it is at 4.080 (.040 overbore). Crank is supposedly cast '73 crank. I need to know if the block can be bored to .060 and can I use '69 or '73 pistons and rods. Are 318 rods the same as 340? I would love to put this thing together but need to know what can interchange due to parts availability. I appreciate the help you. This is one great mag.
Scott-
Can the block be bored 0.060"? Sure. Is this a good idea? Probably not, you'd need to sonic check it to find out wall thickness, core shift, etc. If the walls are at least 0.075" thick after the new bore job, that would be the bare minimum for a near-stock-HP buildup. To make any real HP, though, you need thicker walls. I've made this point so many times I'm getting a little bored myself: Any small performance advantage from the extra displacement gained by an overbore will be much more than lost if the cylinders are flexible and the rings don't seal!
Late 318 rods are similar to 340 rods (they are basically 360 rods). '60s / early-'70s ones are not, they are significantly weaker.
You can use virtually any combination of reciprocating parts that can be balanced. The cast crank is also plenty strong enough for your lowbuck-sounding buildup. However, the extra hassles of the external balance components, etc., might still make it worthwhile to go with a forging.
Rick
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