Last fall I finally got a 350 for my Camaro. It came with an automatic flexplate which I'm tossing for my T-5 flywheel. What I need to know is if I need to have the flywheel balanced or replace the damper due the engine being internal or external balance. Not sure if the flexplate on a 2 piece seal was ever part of the balancing. The casting on the block is 3970010 and to my knowledge, it's factory stock.

 

It's internally balanced, unless someone did something silly during a rebuild.

 

Ok, one less thing to worry about. So was it just the factory 400s that were external then?

 

For the 2 piece RMS era, yes.

 

The newer, one- piece rear main seal 350 engines have a slight bit of weight spot welded on the flexplate because the crankshaft flywheel mounting face is a perfect circle. This not as much as the weight that you find attached to a 400 or 454 flywheel/flexplate.

On the older two- piece rear main seal engines the flywheel mounting face of the crankshaft has an offset, squarish portion hanging out radially, which provides just a touch of needed extra balance.