To get a 350, you need to start with a 350 block. However, you can *use* parts from a 305 in a 350 rebuild, provided they are compatible. Here's what you'd need to do to build a 350:
1. Source a 350 block: This is the crucial first step. You need a good, sound 350 block to build from.
2. Disassemble the 350 block: Completely disassemble the engine, carefully cleaning and inspecting each part. Note: You might *reuse* some parts from your 305, like some accessories or the intake manifold, *if they are compatible* with the 350 (this is not always the case).
3. Machine work: The block will likely need machining (boring, honing, decking) to ensure proper clearances and tolerances. The crankshaft and connecting rods may also require machining.
4. Parts selection: This is where careful planning is necessary. You'll need to select the correct components for a 350:
* Crankshaft: A 350 crankshaft is longer stroke than a 305 crankshaft and absolutely essential.
* Connecting Rods: 350 connecting rods are generally longer than those of a 305 to accommodate the longer stroke.
* Pistons: 350 pistons are designed for a larger displacement and will be taller than 305 pistons.
* Rings: You'll need new rings matched to your pistons.
* Bearings: Main and rod bearings must be properly sized for your crankshaft and connecting rods.
* Cylinder Heads: While 305 heads *can* technically be used on a 350 block, it's generally recommended to use 350 heads for optimal performance. The combustion chamber size and flow characteristics will be better matched.
* Valvetrain components: Cam, lifters, pushrods, rocker arms. These should be chosen based on your desired performance goals.
* Gaskets and seals: All new gaskets and seals are essential.
5. Assembly: Reassemble the engine carefully, following proper procedures and torque specifications. This is a complex process requiring precision and knowledge.
6. Balancing: It's highly recommended to have the rotating assembly (crankshaft, pistons, connecting rods) dynamically balanced to ensure smooth operation and prevent premature wear.
7. Break-in: After assembly, the engine needs a proper break-in period to ensure the rings seat correctly and the components wear in properly.
In short: You're not "rebuilding" a 305 *into* a 350. You're building a 350 engine using potentially some parts (carefully selected) from your 305 along with all the other necessary 350 specific components. This is a significant engine building project requiring specialized tools, knowledge, and precision. If you lack experience in engine building, it's strongly recommended to seek the assistance of a professional engine builder.
