How to Build a High Horsepower Small Block Chevy Motorby Moss Strohem
Building a high-horsepower small block Chevy engine requires careful planning and research. Today, experienced engine builders can attain output of more than two horsepower per cubic inch with thoughtful design and attention to detail. "Stroker" combinations -- using crankshaft strokes longer than standard -- allow displacements of well over 400 cubic inches, and outputs beyond 800 horsepower. Competition crate engines in this category from reputable builders cost well over $25 per horsepower.
Designing the Short-block Assembly
Plan the engine build that suits your budget, displacement and power goals. You can typically design engines based on the factory blocks for displacements of 383 or 406 cubic inches. These engines can produce 500 horsepower or more with fairly common aftermarket parts.
Purchase an engine block capable of withstanding the targeted power output. You can use a suitable factory block for up to approximately 600 horsepower -- less for stock-car or circle track use. For power goals beyond that level you should use aftermarket blocks for two reasons: they have specific design changes that make them suitable for large-displacement and high horsepower, and the added cost for the precision machining and preparation of a factory block may not be justified. You may have a total expense nearing the cost of an aftermarket block, but you will still have a block with limited strength and power capacity.
Select a rotating assembly -- crankshaft, rods and pistons -- with the stroke and bore -- piston diameter -- required for the desired output. Choose a forged steel crankshaft, forged steel connecting rods with upgraded rod bolts, and forged aluminum pistons for extra strength. For an engine to run on pump gasoline, you should target a compression ratio of no more than 10-to-1. Racing engines with extremely high compression ratios require high-octane racing fuel.
Take the engine block and rotating assembly to a qualified performance engine machinist for inspection and "blueprinting." Blueprinting involves measuring and machining all critical surfaces to precise specifications. Blocks with stroker crankshafts may require grinding for additional clearance. Have your machinist balance and blueprint the rotating assembly. Finish-machining crank journals, rods and piston-pin bores to exact tolerances ensures proper oil clearances. Balancing the assembly adds reliability and frees up extra horsepower.
Heads, Camshaft and Induction System
Choose aftermarket cylinder heads that provide optimum airflow and air velocity to reach your horsepower goals. The ability of the engine to breath is the key to producing power. A rule of thumb is 0.5 cubic feet per minute of flow for each cubic inch of displacement. Choose even higher-flow heads for high-rpm competition engines.
Select an intake manifold and carburetor that have sufficient flow capability for the intended engine. They must be compatible with the airflow potential of the cylinder heads. A single-plane manifold is generally better for competition, wide-open-throttle applications, while a "high-rise" dual-plane manifold works well for "hot street" engines.
Choose the camshaft. This selection is critical -- the cam determines the "character" of your engine, and in what rpm range it produces its power. A cam that is too small or too big for the heads won't produce as much power. Consult with the head manufacturer, engine machinist or a custom camshaft designer for recommendations. Provide as many details as possible about the engine configuration and its intended use.
Assemble the engine according to the instructions in your performance engine building manual. Check and re-check all clearances and fitments. Test assemble as many times as needed to be certain there are no issues. An alternative is to have the engine machinist assemble the engine. His expertise may justify the expense, because he will have the experience and equipment to correct any concerns.
Items you will need
- Aftermarket engine components
- Performance engine assembly manual
- Engine assembly tools
- Engine Builder Magazine: "A Chip Off The Old Block: Aftermarket Blocks Are More Versatile Than Ever"
- Car Craft: "Build A Small-Block Chevy"
- Engine Builder Magazine: "Performance Drag Racing Heads"
- Wallace Racing: Estimate Intake Airflow needed from Horse Power wanted
- Engine Builder Magazine: Understanding Crankshaft Balancing