How to Get the Most Horsepower Out of a 454 Chevy Engineby Moss Strohem
Introduced in the 1960s, the Chevrolet big block engine has been used in both performance and full-size cars as well as trucks. In 1970, GM increased the crankshaft stroke of the 427-cubic inch engine and achieved a displacement of 454 cubic inches. With aftermarket components, it is possible to build engines designed on the 454 platform that are well in excess of 500 cubic inches. In staying with the standard bore/stroke combination of 4.25/4 inches, however, it is not uncommon to yield power outputs of greater than 650 horsepower from the 454 in race engine configurations.
Determine the power output desired. The factory high performance GM engine components are capable of supporting well over 500 horsepower, and the early LS6 Chevelle engine was rated at 450 horsepower. Factory crankshafts, connecting rods and pistons can support more than that when properly machined and prepared.
Machine the engine block and internal rotating assembly for correct clearances for high output usage. Careful detail needs to be given to block alignments and specifications as well as the clearances of bearing surfaces for the rods and crank, camshaft and the piston-to-cylinder wall clearance. Clearances that are too tight must be avoided.
Consult---as an alternative---with a reputable engine builder/machinist who is familiar with the 454 BBC. A machinist can provide ready-to-assemble short blocks built to predetermined specifications and with a piston designed to achieve the desired compression ratio. Note that higher compression ratios produce more torque and horsepower but require high octane fuels.
Select a cylinder head with airflow characteristics that support high horsepower output. Not all factory production heads are suited to high horsepower production; however, there are several choices available from aftermarket vendors. Generally speaking, a head with 290 to 320 cc intake port volumes will allow high RPM airflow and maximum horsepower outputs in a 454-cubic inch engine. "Smaller," street-oriented heads will produce lower RPM torque at the expense of high RPM power.
Choose a camshaft that is designed for the intended RPM range the engine will be most typically used in. For a street-driven engine that sees only occasional full-throttle runs to 6,500 RPM, select a camshaft that is designed for an RPM range that is lower and broader. Race applications, such as drag racing, however, have operating ranges of perhaps 5,000 to 7,500 RPMs only. While they may generate more horsepower, the application is very concentrated. This cam design will not work well on a street/strip engine.
Select the intake and carburetor system. A dual-plane manifold that generates more low-end torque works well on the street (or in a tow truck) but will not flow enough air at high RPM to permit larger heads and cams to work well. A single-plane (open "plenum") manifold design and carburetor that flows 850 CFM or greater will produce more horsepower.
- High power output lies in a solid combination of heads, cam and induction (intake manifold and carb), but the lower-end (short block) must be capable of supporting that power output. If upgrades to the short block are necessary, it may be worthwhile to consider installing an aftermarket "stroker" crank to gain even more displacement. This has become very commonplace to the point that a 454 BBC is considered a small BBC performance engine.
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