Here’s the deal, 4.150 eagle crank, eagle 6.76 rods and 4.5 Cp pistons. Total weight is 1853 grams
Same crank, eagle Hemi rods 6.86 and Ross pistons, weight is 1876 grams. Pistons are close 3 grams but pins are 12 grams different, So the rods are the big difference (tried doing the big and small end weight but I need a good pivot). My question is the 23 grams gonna make a big difference for a street engine balance? This was adding the bearings locks and rings for each combo.
Thoughts?

Yeah it will.

Brian, i have read about overbalancing, which leads me to belueve there is a window of sorts to work within. Could you comment on that? ( Is over balance a condition of heavier counter weights, and if so, what do you consider "acceptable"

If What you are saing is that a total bob weight is off 23 light, and one piston and pin is 15 grams of it, that leaves 8 grams which at least for the bottom end of the rod is 4 grams each. Thats pretty close( within what the factory had) and could be worked out but good thing is its piston and pin (reciprocating) where most of the error is. Bad thing is you crank is light If its off I believe heavy on the crank is better. Think about it we always toss some on for oil at the end.

The new rod-piston combo is 23 heavier, new Hemi pin is 150, old flat top pin is 138. New rod (same manufacture) is heavier. I’m thinking I’ll take the parts to get it balanced again, shouldn’t be to much work other than adding a little weight to crank

The new rod-piston combo is 23 heavier, new Hemi pin is 150, old flat top pin is 138. New rod (same manufacture) is heavier. I’m thinking I’ll take the parts to get it balanced again, shouldn’t be to much work other than adding a little weight to crank [/quote]
It is way better to be safe now than wish you had been later when somethings go bang, especially with a Hemi motor

You can't know what a bob weight is without the big and small end weights, although it's probably not the case here you could have a lighter bob weight which is the number that maters and still have a piston and rod that weigh more overall. Only 50 percent of the reciprocating weight is counted but 100 percent of the rotating is counted. I own a machine shop and crank balancer and do this work frequently. an under or over balance from 48 to 52 percent or so would be unnoticeable under anything but the most extreme conditions. The heavier the crank and bob weights are the less a little out of balance matters, and BBMs are among the heaviest of all common V8s.

Thats what I was trying to say. if you take the the 15 grams he knows is in the reciprocating and call that a wash(well within the % factor) and assume that all the rest is in the big end(worst case case because if any of it is in the small end it becomes wash also) It can't be that far out or that bad.

But if you want it better by all means get it spun up. If you set the machine to remove weight see what it shows you might be able to take off the rod pins(crank) instead of adding.

I’m thinking of pin too 12 grams wedge piston is a tapered .990 pin, Hemi is 1.03 straight but piston is lighter, piston-pin on Hemi is only 3-4 grams different. A wash in my mind, so big difference is the rod. I’ll make a fixture to balance the big end and bottom separate, assuming rod needs to be 0 degree horizontal.

Not what I'm saying. The wash is the recip. is heavier now but within the % over/under balance. The rotating is off ...but it can't be much.Once you get the actual numbers you have an idea of the amount of under balance the crank will have.

I did a balance on rod, each end. 10 on big end and 6 on pin, whole rod is 16 grams different total

You better get it balanced, cause that don't jive with your original post. Unless I'm reading something wrong. You have 26 gr in rod bob weight difference alone.

My digital scale jumps around a bit