the crank determines the imbalance.
the stock crank in our cars are 50 oz imbalance
most after market cranks are 28 0z imbalance.
I had my rotating assembly balanced at the mach shop before assy.
i have an eagle crank rods etc. How do i know what balencer i should get. I had the stock flywheel on it. So should i just get another 50oz one? (mine is shot so i'm also looking for a new one...)
If the car was balanced using the stock flywheel then it is a 50oz.
You basically determine the balance when you have the rotating assembly balanced at the machine shop. You can balance almost any crank to 0, 28, or 50. It all depends on how much work it will need to get there.
If you use a very light rod and piston the crank may need Mallory to make up the weight to go 0. Most aftermarket strokers go to 28 becuse you do not have to remove as much material.
The new Eagle 4340 internal balance cranks will go to 0 fairly easy since they are made heavy, and you do not have to add any Mallory which gets expensive.