How do you turn a Chevy 350 to 355?

You don't "turn" a 350 into a 355. The displacement difference is achieved by increasing the bore of the cylinders. A 350 small-block Chevy has a 4-inch bore and a 3.48-inch stroke. A 355 typically has a 4.00-inch bore and a 3.50-inch stroke.

Therefore, to get to 355 cubic inches, you need to:

1. Bore the cylinders: This requires machining the cylinder block to increase the diameter (bore) of each cylinder. This process requires specialized equipment and expertise. You'll need to find a machine shop that specializes in engine work. Simply boring to 4.00" will get you close to 355 cubic inches, but will require using slightly oversized pistons.

2. Use new pistons: The larger bore requires pistons with a correspondingly larger diameter. These must be properly sized for the bore and the connecting rods. The piston selection also affects the compression ratio.

3. Possibly use a different crankshaft: While a standard 350 crankshaft *can* be used with a 355 build, a crankshaft with a slightly longer stroke (3.50 inches, like in a 383) is sometimes preferred for increased displacement. If you use the standard 3.48" stroke the displacement will be closer to 350 cubic inches. Note that using a longer stroke crankshaft requires careful consideration of the connecting rod length for proper piston-to-cylinder wall clearance.

In short: It's an engine rebuild, not a simple conversion. You'll need professional machine work, new pistons, potentially a new crankshaft, and all the associated gaskets, seals, and other components necessary for a complete engine rebuild. This is a significant undertaking requiring mechanical skills and/or access to a skilled engine builder.