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I have a very simple question for the engine builders. What kind of balance did you use to weigh pistons and connecting rods? I am presently doing a 383 and according to the literature it needs to do this. I don't plan to race but I want to do it right since I am looking for something close to +/- 450hp.
The rods and pistons are usually somewhat close depending on who made them. But the crank can be all over the place. If you are installing lighter stuff than stock it's not a big deal unless you go crazy. If heavier than stock it can get into a mess. If it's an aftermarket crank, which most likely it is, they have no idea what parts you will put with it and if you're lucky they left it slightly *heavy* and it will be easy to balance. If not it may require mallory metal to get it right.
I'd go find a good shop to balance the assy. If the parts people tell you it needs to be done, then that means they made no effort to get it close by parts selection. You also need to know if it was designed to be internally or externally balanced like a stock 400 crank. Then you will need to have correct balancer and flywheel/flexplate.