The Chevrolet 305-cubic inch motor has never been a top choice among performance engine builders for a number of reasons, but it can produce very respectable power given the right combination of parts. "Hot-rodding" a Chevrolet 305 requires a complete engine tear-down and rebuild from the ground up and requires very specific part selections in order to produce a race-ready engine. This engine has been recorded as producing upward of 500 horsepower and has led plenty of race car drivers to first place finishes.
Remove all engine parts to expose the bare engine block. The block will need to be "hot-tanked" or professionally cleaned prior to performing any work on it. At this point the engine block is ready to be machined, starting with boring the cylinders to 3.80 inches in diameter to ensure wall evenness. The crankshaft journals will need to be trued as well as the camshaft journals.
Replace the crankshaft bearings and install a new crankshaft. Make sure the replacement crankshaft has the same specifications as the factory-installed crankshaft or the engine will no longer displace 305 cubic inches.
Install new camshaft bearings and a replacement camshaft. In order for the engine to produce high horsepower and torque, an aftermarket camshaft will need to be installed. The camshaft is the most important part of the engine and determines where in the rotations per minute (RPM) band the engine will produce its power. A camshaft with the following specifications will work best for this application: valve lift (intake) .510, (exhaust) .520, duration (intake) 210, (exhaust) 214 at .050-lift duration and 114 degrees of lobe separation angle. Any camshaft designed for a Chevrolet 305 will work, but due to the low cubic inch displacement and long stroke of the 305, the abovementioned camshaft is the best choice.
Install swirl port cylinder heads. These cylinder heads came standard on most post-1987 Chevrolet 305 engines. Swirl port heads are both ideally suited for this engine build and easy to find. Before installing, make sure to perform a three-angle valve job and port at least the exhaust inlet as these heads have small exhaust passages that hinder exhaust airflow. Replacing the valves and valve springs is optional but recommended as these items tend to wear out on older engines.
Add a dual-plane, aluminum intake manifold. Do not install a single-plane or high rise intake on this engine as this will severely lower the engine's output. These are high-performance parts common to racing engines but are not designed for small displacement engines, such as the Chevrolet 305. There are many different styles of intake manifolds that will work for this application and the choice of one is purely personal preference.
Install a four-barrel carburetor capable of flowing at least 650 cubic feet per minute. The choice of carburetor is up to personal preference.
Add a set of quality exhaust headers with 1.75-inch primary tubes and 2.5-inch collectors.
