Mopar Action On-line – Tech Questions
Scott Marshall, Wills Point, TX, 1971 Dodge Dart Swinger 225
I recently purchased a 340 block and crank, the date codeon the block is 7/10/69. I checked bore of block and it is at 4.080 (.040overbore). Crank is supposedly cast ’73 crank. I need to know if the blockcan be bored to .060 and can I use ’69 or ’73 pistons and rods. Are 318rods the same as 340? I would love to put this thing together but need toknow what can interchange due to parts availability. I appreciate the helpyou. This is one great mag.
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. Ifthe walls are at least 0.075″ thick after the new bore job, that would bethe 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 alittle bored myself: Any small performance advantage from the extradisplacement gained by an overbore will be much more than lost if thecylinders 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 bebalanced. The cast crank is also plenty strong enough for yourlowbuck-sounding buildup. However, the extra hassles of the external balancecomponents, etc., might still make it worthwhile to go with a forging.