How to Tell the Difference Between a 327 and a 307 Chevy

Identify the difference between a 327 Chevrolet and a 307 Chevrolet vehicle primarily by measuring the engine's cylinder head bore size. This is where the two models differ most significantly. Remember to locate the serial number before you attempt any diagnostics within the engine. This provides a simple, fast method of differentiating between the two cars without the need to alter anything mechanically, or take out individual components and measure them.

Instructions

1

Check the serial number on the engine. Open the hood and look inside at the engine. You should see a serial number printed on the surface of one of the cylinder heads. The number will have either 327 or 307 at the end of it to differentiate the engine types.

2

Disconnect the PCV valve from the cylinder head cover. Remove the brake servo vacuum line and unscrew the six bolts holding the cylinder in place using a wrench. Detach the cylinder head cover. Use a specialist cylinder head tool to lift out one of the cylinder heads. To complete this, you will also need to guide the timing chains and the chain guides out through the timing chain housings, as explained by Kulls .

3

Measure the bore size of the cylinder head with a length of measuring tape or a ruler. The 327 Chevrolet will have a larger bore size than the 307 model. Specifically, 327 models were the first models to have 4.00-inch bore diameters, according to Monte CarloSS. 307 Chevrolets have 3.88-inch bore diameters.

4

Identify whether or not the engine has small journal cranks. If it does contain this component, you are most likely to have a 327 Chevrolet, and if it does not, you are likely to have a 307 model. Check the year of manufacture for best results, because there are exceptions to this rule. 1968 to 1973 Chevrolets, for example, both contain large cast block engines, according to Nastyz 28.

5

Look for wear and tear on the cylinders and signs of cracking. 307 engines are prone to cylinder wear and heat-related cracking because they were not built with tin or chrome in the block alloy.