Flywheel 4.9 vs 302

Installed a new 4.9L with a rebuilt C-6 AT transmission on my 1980 f100. Have a significant vibration. How can I tell by looking through the inspection window if I received/installed the right flywheel for this motor and not for a V8302?

If you look on a site like RockAuto you can look at pictures of each flex plate to see the difference between them. Basically they will be the same except the 302 flywheel will have a balance weight welded to it. I think it is on the inside or engine side.

This is what I got from the transmission shop. Looks like a 302 or 351

Socnarftrucks wrote

This is what I got from the transmission shop. Looks like a 302 or 351

I would say so, yes. And it will cause a 300 to vibrate for sure. A 300 flexplate should not have weights welded to it like the 302 or 351 flexplates. I would say by the size of the weight on yours it is for a 351 or earlier (pre-1982) 302.

351 Flexplate:



302 Flexplate:



300 Flexplate:

Size is exactly the same, V8  engines use weights, 6  cylinders do not. You can cut the weight off and you'll be good to go!