Technical 700r flexplate on a 305??

I have a turbo 350 trans that I am putting in my 56 chevy truck. My engine is a 90 HO 305. I have a flexplate from a two piece rear seal 350.. Will it work on the 1 piece crank on the 305? Thanks

 

In short, no.

 

Exactly.^^^^

the 305 is an external balance engine and even the flexplate from a one piece sealed 350 ci motor will not work properly.

 

The bolt circle and center hole were intentionally changed to make this impossible. Not just to give you a headache, either.

Remember the oddly shaped flange on the the back of an SBC crank? That's a counterweight.

In order to make it possible to slip on a one-piece seal from the rear, that weight could not be there, but the mass of that weight had to go somewhere.

That mass was relocated to the flywheel/flexplate.

Most SBC's with two-piece rear main seals are internally balanced, meaning the dampener and flywheel/flexplate are zero-balance.

The one-piece seal SBC's are external balance.

Flexplates are pretty cheap. Summit is not far.

 

That is about as good an explanation as you could possibly receive right there by Gimpyshotrods.

 

TH350 or 700R4 doesn't make any difference on the flexplate. They both use the same bolt pattern at the converter lugs. Although the TH400 uses the larger bolt pattern, and some TH400 flexplates won't work with the TH350 or 700R4.

The year of the engine does matter. Up to 85 or 86 they used the big bolt pattern two piece seal. Starting 86 or 87 they used the small bolt pattern one piece seal. Flexplate has to match the engine.

 

Thanks, off to napa for a 305 flexplate. Thanks