Get 400 HP From a Chevy 350
The Chevrolet 350 engine was introduced in 1967 and was produced until the early 2000s. In basic, standard-performance versions, it produced around 250 gross horsepower and over 350 horsepower in high-performance versions for 1970 “LT1” Corvettes and Z28 Camaros. With the goal of 400 horsepower in mind, it’s reasonable to duplicate the LT1 350. That engine featured stronger internal components to withstand the more demanding performance, which was achieved from increased compression and greater airflow from the cylinder heads, intake system and camshaft/valve timing events. With careful selection of engine components, attaining 400 horsepower or more is well within reach.
1. Locate and purchase a late-model 350 engine that is in good running condition. Newer-design engines — especially GM 5.7L Vortec 350s from late 1990s trucks and vans — have cylinder heads which can out-perform the best high-performance heads from the late 1960s and early 1970s.
2. Remove the cylinder heads and take them to a performance engine machine shop. Specify the goal of 400 horsepower and have a performance valve-job completed. If using Vortec heads, have the valve-guide bosses machined enough so that a higher-lift camshaft can be used. Also, have the head surfaces milled/machined to reduce the combustion chamber volume reduced to achieve a compression ratio of approximately 10 to 1. This process depends on the type of piston in the engine and thickness of the head gasket, so be certain to consult with the machinist.
Alternately, aftermarket performance heads may be substituted.
3. Select a camshaft and lifters that will be suitable for the type of driving the car or truck will see most of the time. While over 400 horsepower can be attained more easily with better flowing heads and a larger camshaft, too large a cam will make the engine difficult to operate. A cam with around 220 to 230 degrees of duration (at .050-inch lift) and about .480 to .500-inch of valve lift will typically be sufficient.
4. Install an intake manifold and carburetor that will be matched to the operating range of the camshaft. A larger volume manifold — plenum and intake runners — will flow more air than a factory-type unit, but one that is too large will cause low-RPM performance to be sluggish. Use a carburetor that flows in the area of 750 cubic feet per minute (CFM) of air.
5. Install aftermarket headers and larger exhaust pipes in mufflers. The exhaust system needs to be as free-flowing as possible. Factory cast iron exhaust manifolds and mufflers are usually fairly restrictive and not intended for high-performance use.
6. Check that the engine is in its best state of tune. The timing needs to be set correctly, and the ignition components and air/fuel mixture need to be correct.