87turboGN

First, I'm new here and I have little knowledge about building a performance car motor. I've searched the internet looking for info on finding the difference between the 305 and 350 crankshaft and spent 2 hours and haven't yet to find anyone who seems to truly know. I can't imagine this not being an ancient question but all I can find is that they are different, but no one seems to know how to tell which one is which. I have a crankshaft on my workbench but I'm not sure if its a 305 or a 350, but I know its one or the other. I don't have both to compare to each other either. Does anyone know the distinction between them? How can I tell which crankshaft I have?

87turboGN

I know that the cast cranks for the 305/350 2 piece seals was 3932442. The difference in balance was in the mass of the counter weights. These engines were internally balanced[info from John Lingenfelter]. The 86-late 305 /350 shared the same one piece cast crank 14088526. I can find no info as to whether the crank throws mass was different on this crank , as it was externally balanced. Does anyone know ?

Most stock 350 rods come in at around 720-740 grams, untouched. 305 rods are about 30 grams (roughly an ounce) lighter on average. If the rotating portion of the rod mass is made smaller, then the crank counterweights have to be made smaller (lighter), to retain equal masses on either side of the axis of the crank. Since a good portion of the beam of the rod appears as rotating mass, it affects engine balance. Piston weight, and small end weight, don't, as they are reciprocating weight. The crank is counterbalanced differently in most 305s to compensate for the the lesser rod weight, not piston weight . That's why even though 305 cranks and 350 cranks are usually made from the same casting (casting # 442), they don't exactly interchange; the counterweights on the 305 one have been ground down farther. You can swap a 305 crank and 305 rods together into a 350 and it will work fine, or vice-versa, since the pistons don't figure into the part of engine balance that the crank has to deal with; but you can't mix the 2. You might get by with a 350 crank in a 305 because you are overbalanced , although the 305 crank in a 350 will be underbalanced and that is the most undesirable condition. Crankshaft weight of both are similar so no specific exact weight pertains to either, so my problem still exists of how to visually identify the 350 crank without anything to compare it to......