I just bought a used Gotham stage2 rebuild and it was balanced with a stock flywheel. I also bought an ACT streetlite flywheel to put on but when I callled the shop manager at Gotham, he said there will be adverse effects if I don't get the motor rebalanced after I swap the flywheels.
However, the stock motor is balanced with the stock flywheel and I doubt everyone that upgrades to a lightened flywheel has the motor rebalanced.
So I just want some outside opinions on whether there will be "adverse effects" from swapping the flywheels or if it will even be noticeable?

 

You need to get a counterweight. It's the stock automatic counterweight. The same counterweight is used for all aftermarket flywheels.

 

We balanced our engines to within 5 grams from rotor to rotor and rotor to counterweight. Mazda allows up to 50 grams of difference between rotors and counter weights. unless the weight of your new counter weight is totally off, you should be okay. However, that defeats the purpose of balancing the engine. If anything, your bearings will wear out faster than a balanced assembly.

 

ACT doest sel their counterweights with their flywheels inless u buy the package. Just buy the ACT counterweight and put it on. THeirs only one way to put it on (cuz there's a sort of key hole), so its super easy.

 

I did receive the counter-weight with it
It looks like a stocker off an auto, it even says 1996 on it

 

pointless that they balanced it to a stock flywheel, the PO should have purchased a counterweight and had the stock flywheel as well balanced to match for allowability to switch to a lightened flywheel later on. the stock flywheel is 24lbs... i wonder if they at least tried to suggest that to him.

 

Not true... We had an assembly that was balanced with the stock flywheel and was 140grams off. The flywheel came directly off the mazda reman. Apparently, the flywheel was resurfaced and was warped. You'll never see it w/o actually spinning it. there're a few reasons why there were so many mazda remans engine out there that only last 12-15k miles before bearing failures. mazda doesn't rebalance their engines on their remans. They simply just put parts back in and assume it is within 50grams tolerance.

 

could a machine shop, with both flywheels in hand, get the lightweight flywheel to the same weight?

that would definitely save you some trouble

 

I'm sure it is possible.....