Just bought a top gun and have vibration/harmonics on port engine at higher rpms. I have checked with bravo drive off and still there, feels just like a bad gimble bearing or u joints.went through the top end-heads,springs,valves ect. new cam and lifters,swaped distributers and wires.and all the front pullys. The engine is a gen6 ( 100hrs since out of crate )and i suspect the previos owner may have used the wrong flywheel. casting # is 3973457n can anyone tell me if this is a compatable wheel for an externally balanced 502. I just dont want to go into this engine unless i have to. thanks

Rudd,
the Gen V and VI use a different balance than the Gen IV, but the bolt pattern is the same and the old flywheel will bolt up. See if you can get your hands on a GM Performance catalog, they show alot of info. Not sure if it will idenify your wheel. But it may. You may be able to find a GM dealer that has one in stock that you could compare your flywheel with.
Hope this helps.
Dick

That is the wrong flywheel. The one you need is 805.
The 457 flywheel is for Mk IV.
I have a few if you need one.
Eddie

Here is the one you need casting #: Nodular iron with casting 809-14096805
buy good arp flywheel bolts too and use 271 Red Threadlocker from loc tite on the bolts and torque them to the right spec.
http://www.jegs.com/i/GM+Performance...96987/10002/-1

Thanks for the info, I suspected thats what the problem was. I sure wish I coud have caught it when the motor was out, but at least I dont have to rebuild.

and can't really tell the diff by looking at them either...just balance weight and holes diff.