Can someone fill me in on how the LT1 rotating assembly is balanced along with the flywheel for auto and manual transmissions? I bought a 383 LT1 and it came with a new flywheel for an automatic which the original owner said was balanced with the internals of the stroker kit. I want to use a T-56 so now I imagine I need to match balance the two flywheels (auto and manual). All the internals and intake/heads are already installed and I am not about to take all this apart. Can someone fill me in on how this works? It sounds straight forward but I do not know much of the technical info on how all this stuff is balanced. I appreciate the help. I spoke to a machine shop near me and they quoted me about $125.. is this

Update - checking back on some emails with the person who built the engine... he said

"The flywheel wasn't zero balanced - so the whole rotating assembly was balanced WITH it. Thus, if you change your flywheel you need to have the new one balanced identical to the one I gave you."

What are my options here? Can this be done correctly any any compitent engine/machine shop?

Get an external balance 383 flywheel for a T56.

Umm, I am the ultimate newbie with this... What do you mean to just get an external balance 383 flywheel for a t-56?

I have the flywheel that came with the T-56 from a 97 trans-am... Can this one be machined?

How can I external balance it if the engine is already assembled? I am trying to avoid taking the entire engine to a shop as I have no way of doing this.

How would a shop know what balance to put on it? If that even makes sense?

Sorry but I def. dont know much about this and I dont want to walk into the shop and just hand the stuff over... I really appreciate those who can explain some more. Thanks!

External balance is a spec value. A competent machine shop would be able to do it.

I'm a little weak on the specifics of a T56 flywheel, whether you can use any old one-piece rear main seal 383 external balance flywheel or if it needs to be something specifically for a T56. With all of the 383 LT1's out there, I can't imagine there being that much trouble finding one.

All factory LT1 flywheels are external balance. What you'd need to do is just get a factory one, take it and the flexplate that's on the engine now and tell the machinist what the deal is. Get as much detail as you can from the previous owner about the specs of the engine and find out any balance info if you can.

All they'll have to do to the flywheel is probably machine some of the weight off the back side of it, or possibly add to it. More than likely they won't have to do anything.

Usually the only time any weight change is necessary on the LT1 flywheel is when you go to an internal balance rotating assembly, in which case the flywheel/flexplate has to be neutral or zero balanced.

Hmm.. ok, I do have the flywheel from the 97 trans-asm T-56 which is factory so I should be ok here and Im almost certain I have the balance info sheet from the machine shop - I got all the paper work for the engine build too. I will look at what info they printed when I get home and I will let you guys know whats up.

I really appreciate the help.. Thanks.

This is backwards. The one-piece rear main seal cranks require the flexplate or flywheel to have a non-neutral balance because of a counterweight that used to exist on 2-piece RMS cranks external to the rear main seal that can't be there with a 1-piece RMS arrangement. Even the original SBC 400 3.75" stroke cranks had that counterweight external to the RMS, plus additional weight on the flexplate/flywheel and damper.

A 1-piece RMS 3.75" stroke crank that is internally balanced would use the same flexplate/flywheel as a "normal" 1-piece RMS 3.48" stroke crank and a neutral balance damper. But, a 1-piece RMS 3.75" stroke crank that is externally balanced would require the additional weight that a 2-piece RMS 3.75" stroke crank needs, plus a weighted damper.

This can be very confusing, mixing the "internal" and "external" balance terminology makes it even worse. We seem to struggle with it about once a month on this Board. But, as noted, it would be best to get exactly what is meant by "externally balanced" from the previous owner. If the damper is a neutrally balanced unit, the odds are very high that a "normal" LT1 flywheel would be what you want.