Reliable Methods (requiring some disassembly or specialized tools):
* Bore and Stroke Measurement: This is the most definitive way. A 327 has a bore of 4.00 inches and a stroke of 3.25 inches. A 350 has a bore of 4.00 inches and a stroke of 3.48 inches. You'll need a bore gauge to measure the cylinder bore and a depth gauge or other tool to measure the stroke.
* Casting Numbers: The block itself will have casting numbers. These numbers vary by year and specific engine configuration, but a good resource like a Chevrolet engine casting number database (easily found online) can help you identify the displacement based on the casting number. This is arguably the most reliable method if you can find and properly identify the number.
Less Reliable Methods (visual inspection only):
* Block Deck Height: The 350 block is slightly taller than the 327, but this difference is subtle and difficult to measure accurately without tools. It's not a reliable way to tell them apart.
* Intake Manifold Bolt Pattern: While both use the same general bolt pattern, some aftermarket intake manifolds were designed specifically for either the 327 or 350. This is not consistent and therefore unreliable.
* Exhaust Manifold Differences: Similar to intake manifolds, some aftermarket manifolds were specifically designed for either the 327 or 350. Again, not reliable for identification.
In summary: To be absolutely sure, you need to either measure the bore and stroke or consult a reliable database using the casting numbers. Visual inspection alone is insufficient to reliably distinguish a 327 from a 350.
