I am planning on building a 350 for my 87 trans. It has a 305 but I want to get rid of it. I am sure there are differences in cranks just not sure what exactly they are. Thanks

 

Balancing is all I've ever heard.

 

The casting is the same; but the counterweights are slightly different, to make up for the lighter rods and pistons. It is possible to make a 350 crank into a 305 one by taking off metal, not usually the other way though. Some 305 cranks (L69 for example) have X rods and therefore are balanced the same as 350 ones.

 

You could use the 305 crank since it's the same stroke as a 350. Con rods are all roughly the same. Since 350 pistons are larger, they'll also be a lot heavier.

Just get it all balanced and it will be fine. Even if you used a 350 crank and went with aftermarket pistons, you would still need to get it all balanced.

 

But what if you threw it all together. Im talkin about a 305 crank and rods, into a 350 with 350 pistoins. Would the engine not run, or would it just not last long at all. I dont want this to seem like a dumb question, I am really wondering this. Also, how much is balancing work. Thanks anyone,

 

It'll run rough. Had that problem, since the cranks are so close except for balancing, accidentally put a 305 crank in a 350. Put a reground 350 crank in from the machine shop, shaking went away. If you get it balanced as an assembly however, that shouldn't be a problem. It's such a subtle difference, its hard to tell without having both cranks sitting in front of you.