How to Build a 350 Race Motor

by John Stevens J.D.

Although building a 350 Chevy for racing purposes is fairly simple, selecting the components is the greatest challenge. Each component must work in unison, and selecting the components depends on the particular racing application. For example, a race motor for circle track racing is very different than one for drag racing. For this reason, it is important to consult with the manufacturer of each component to find the most appropriate part. However, there are specific parts which should be considered in any race application for a 350 race motor.

Step 1

Replace the stock two-barrel carburetor with a four-barrel carburetor or, if the engine is already equipped with a four-barrel carburetor, a larger carburetor. Carburetors are rated by cubic feet per minute, or “CFM,” which refers to the amount of fuel the carburetor can process. A common mistake is to assume that larger is better because too much fuel is even worse than not enough fuel. Since the size of the engine is already known, provide the carburetor manufacturer with the intended purpose of the engine, which will tell the manufacturer which size is best.

Step 2

Replace the stock cast-iron intake manifold with an aftermarket aluminum manifold. Aside from the lighter weight, aluminum manifolds allow the air/fuel mixture produced by the carburetor to flow into the cylinder heads easier than the stock manifold, which helps the race engine reach higher engine speeds.

Step 3

Replace the stock cast-iron cylinder heads with aftermarket aluminum heads. The principle is the same as with the intake manifold. The aluminum heads will reduce the vehicle’s weight and allow the air/fuel mixture to reach the cylinders faster. Cylinder heads are available with different-sized valves. Larger valves are typically better for racing applications than smaller valves.

Step 4

Replace the stock distributor with a high-performance aftermarket distributor. Simply put, the 350’s stock distributor will not be able to power a high-speed racing engine. An aftermarket unit will ensure that the spark plugs receive a consistent spark.

Step 5

Replace the stock cast-iron pistons with forged pistons with a higher compression ratio. The higher the compression ratio, the more power generated by the engine. However, a higher compression ratio increases the risk of pre-ignition, where the air/fuel mixture ignites before the spark plug fires. Pre-ignition can quickly destroy an engine. To prevent pre-ignition, race fuel has a higher octane rating than pump gasoline. A compression ratio of 10:5:1 is as high as the engine should use with pump gasoline. Higher compression ratios require race gas. The 350’s stock cast-iron pistons will not withstand the increased compression ratio and engine speeds, and should therefore be replaced with forged pistons.

Step 6

Replace the stock camshaft with an aftermarket camshaft. The camshaft determines how far the valves in the cylinder head open and for how long. This is often referred to as “lift” and “duration.” Choosing the proper camshaft is probably the greatest challenge. It is imperative that an aftermarket camshaft manufacturer be contacted for advice here. Be prepared to tell the manufacturer about the number of CFMs the carburetor flows, the specifications of the cylinder head and the compression ratio of the pistons.

Step 7

Replace the stock fuel and oil pumps. Too often race engines are built with horsepower in mind. Reliability is of the utmost importance, particularly with a race engine which reaches engine speeds much higher than the stock 350. The engine will need more fuel than a stock engine. Fuel pumps are rated in “GPM,” or gallons per minute. Generally, the higher the GPM the better, but again, consult with the manufacturer. An aftermarket oil pump is also necessary to ensure that the engine has an adequate oil supply.

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