what needs to be changed in a 72 340 to be like a 70 340?

340butterduster said

and balancing man that was a crap shoot. 'Cuz they sure weren't balanced when they were built, (and that makes a world of difference).

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I never knew how bad the balance was in my original standard bore 340 until I dropped in the stroker engine. So much smoother going down the road. It is incredible how smooth a correctly balanced engine is. And the stroker kits that come balanced, yeah, that is like a factory balance, total crap. You have to have a good shop balance it correctly if you want it balanced.

Balancing also takes a lot of stress off that bottom end too. And less rattles in your car so that is nice.

Did I mention those standard 340 pistons are HEAVY.