Hot Rods Balancing Assembly 383 SBC

Got a balancing questions regarding pistons. I have a set of forged pistons for a 383 kit. 6 weigh in at 455 grams and 2 weigh 450 grams. Does this need to be addressed before assembly?

 

Depends - do you have 2 heavy rods you can pair up with the light pistons?

 

Nope.
More important the crank is balanced to piston and rod weight.

 

I'm probably overkill...but whenever I build an engine, I address all the rotating/reciprocating masses first. All pistons are removed of excess material to bring them all down to the lightest piston weight. Then the small and big ends of the rods go through the same process. I then give the weight information to the crank balancer. It doesn't cost me anything but time.

 

Without much details the answer is maybe. Unless you have a weight matched rod set it's likely if you weight checked the rods you would find more of a variance than with the pistons. As to if it matters, depends on your intended RPM range you plan to regularly buzz.

 

You should lighten the other 6 pistons to match those two. Then you should balance the rods so they match too. Thats the right way to do it. Any weight you remove from the pistons and rods may help you with the balancing because it might help you be light enough not to need expensive mallory weight to get the crank balanced. Mixing and matching weights will work if there isn't too much disparity, but the best way is to make them all interchangeable weight wise. Remember there is both reciprocating weight and rotational weight, so its not just having equal weight but having it in the same places.

 

This is the correct advice of what should be done. You didn't mention if you bought a crank kit that gave you bob weight info. You can modify and weigh the pistons pretty easily. For the rods you need the weight of each end and that requires a fixture to do correctly. So, if this is a build you want to do everything as it should be, match the pistons and send it out to be balanced. If it's more of a mild budget build, match the pistons and put it together. Your biggest risk with that approach is that your pistons and rods don't get you in the ballpark of the intended bob weight to witch the crank was balanced. FWIW, I balance all my engine assemblies and many of the parts combos do take heavy metal to get correct. So, without some details it's still a bit of a maybe.