will it be possible to use a 305 flywheel and starter on a 350 block

 

yes however i assume you have a flex plate (automatic right) Pretty much everything from a 305 will bolt to a 350 including the flex plate and starter.

 

'86-earlier and '87-later will not swap (305 or 350 doesn't matter).

 

Before 1986, small blocks were internally balanced, thus there are no counter weights on the flywheel/flexplate. 1986 and up cars were then externally balanced...and if you use this flywheel on, say a 1970 350 block, you'll get heavy vibration. The flywheel from a pre-86 engine will be smaller in diameter also, and the starter will not line up even close. Hope this helps...enjoy....

 

I've got one:
I am getting ready to start a swap in a 91. It has a 305 w/ 5spd. I am putting in a 78 350 and keeping the 5spd. What flywheel do I need to use?

 

If you have a two-piece rear main seal engine, use a flexplate/flywheel for '82-'85 application 3rd gen. It will be 153-tooth, 12-3/4" diameter and will be neutrally balanced.

If you have a one-piece rear main seal engine, use a flexplate/flywheel for '86-'92 application 3rd gen. It will be 153-tooth, 12-3/4" diameter and will be counterbalanced. (To say one-piece rear main engines are "externally balanced" is only half true - the harmonic damper is neutrally balanced, unlike factory SBC 400's which are truly externally balanced front & rear.)

You can't bolt the wrong one on the engine. The bolt pattern also changed.

 

NO. The 400 was externally ballanced. The difference between the 86 & earlier and the 87 & later is the rear main seal. In 87 & newer, the rear main is one piece, and the flywheel has a smaller bolt circle. The 305 & 350 are all internally ballanced.

 

Why is this on the carb forum???

 

I agree, kinda trans related, but I cant complain. So I can use a flywheel slated for a 82-85 3-gen 305, on a 78 350? Is that right?

 

Yes.

However, there are reports of a lot of mid->late 70's SBC's with mis-located starter mount holes. If the engine is out, you might want to get that checked by a competent machine shop.

 

Thank you. I will make sure we watch for that. Is there any easy cure, if that is the case. Or is it something the machine shop will have to fix?

 

Thanks for the correction...I was under a bit of a misconception then. Why was my buddy's 86 305 externally balanced though? I'd gathered my information on the issue from elsewhere but the occurence with his flywheel being weighted seemed to solidify what I had learned. Get back to me....

 

Two-piece rear main seal cranks have a cast-(forged-)in counterweight outside the oil pan just in front of the flywheel mount flange. Since you can't slip a round one-piece seal around a counterweight, the factory put the weight on the flexplate/flywheel when they went to the one-piece seal design.

That's why I said, "To say one-piece rear main engines are 'externally balanced' is only half true ..." The flexplate/flywheel for one-piece is weighted, but it's not the same counterbalance as you'd need with a "real" externally balanced engine.