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The real answer is that most replacement pistons are made to be the same weight as the pistons they're replacing. So you should be able to swap pistons as long as you don't spend big money for lightweight pistons. Chrysler Corp factory balance jobs were notoriously bad, but the engines still performed.

Now depending on how much $ you have to spend, it would make a better engine if you DID buy lighter weight pistons and have it rebalanced. But on the cheap, swapping stock replacement for stock replacement doesn't require balancing.
Think of the millions of factory rebuilt engines on the road and not one of those engines was rebalanced.

R.



Good info for sure. Thanks for posting Dogdays
I just looked and the stock 71 hi compression piston in a 340 weighs 758 grams and the KB pistons weighs only 507 grams. I'd consider the KB243 a stock replacement piston at only $263 dollars a set.

Definitly would need to be rebalanced for competition and hi rpm use.

My street driven 340 has been a reliable motor even though it has not been re balanced with the new lighter pistons.
I even own the fixtures and scales to determine bobweight. Just not the balancer...yet.