Seanhoff

New here! First post, really looking for some technical help with an engine. I own an 88 royale but that's not what I'm working on today...
Okay, so vehicle is a 1990 caddilac brougham with oldsmobile 5.0 (307), spun rod bearing 1. I am very experienced with SBC engines, I have never been in an Olds engine before today So before I start planning parts and building I need to ask some experts a few things about these specifically..
biggest question, is the 307 to 350 difference just the stroke like a sbc? AND will an older 350 crank fit into a newer 307 block? I don't know a lot about rocket engines, but from what I can gather the 350 stopped being made early or mid 80s and the 307 was made until 1990, did the block change at all during that time?
Any help is appreciated!!!

olds 307 and 403

A small block Oldsmobile share the same 3.385" stroke. That is a 260-3.5" bore, 307-3.8" bore, 330 3.938" bore, 350-4.057" bore and 403-4.351" bore. As you can see, the bigger the engine, the larger the bore and better breathing. There is a 4" stroker crank from Cutlassefi but with pistons and rods, an easy 3 grand for the reciprocating assembly. Yes, a 375 ci Olds 307 is possible, just not cheap.

joe_padavano

Forget everything you know about Chebby motors, because it doesn't apply here.

As noted above, no, the blocks are not the same. The least expensive way to increase displacement is to swap in a 350 or 403. Stroking a 307 with an aftermarket crank is a huge waste of money,

67OAI

So the above posts have discussed the difference in the Oldsmobile blocks of that series engine but I think you are asking if you can just put the 350 crankshaft into the 307 as a replacement because of the spun bearing. Yes, the stroke length is physically the same but I can not tell you if the piston and connecting rod weights are the same which would affect the balance. I would expect them to be the same; perhaps someone else viewing your thread would have that information. Since you have stated that there is a spun bearing, you know that as a minimum the affected connecting rod and the rod next to it would have to be reconditioned or replaced as well!

joe_padavano

The balance will be different between the 307 and 350 rotating assemblies.