How to Build a Chevy 305 for Mileage

by Richard Rowe

Chevrolet's small-block engine can be rebuilt in a number of ways. The first-generation small block had been in production for nearly 50 years when it went out of production in the late 1990s, making such engines cheap to buy, cheap to modify and more versatile than perhaps any other V8 in history. While the 305 drew the unfortunate lot of playing second banana to its 350-cubic inch brother, it's still capable of delivering excellent efficiency and street performance belied by its humble output figures.

Bore the cylinders. Begin with any 1980s 305 engine. Send it to a machine shop and have them bore the cylinders 0.030-inch over, align-bore the mains and mill the cylinder head mating surface flat. Purchase a set of forged race pistons designed to deliver 11:1 compression with a 54cc combustion chamber. Have the connecting rods smoothed, polished and shot-peened to increase strength and have your machine shop balance the crankshaft/rod/piston assembly.

Purchase a set of aluminum L98 cylinder heads, which you can find on any 1985-1991 Corvette. These heads are among the most efficient available short of the newer Vortec design, but the Vortecs require a bespoke intake manifold and exhaust setup. Using aluminum L98 heads instead of their iron equivalent will shave about 50 pounds off of your engine. Install new valve springs onto the heads.

Coat the combustion chamber roof on the cylinder heads, the piston tops and the insides of the heads' intake and exhaust ports with thermally insulating ceramic powder-coating. This will reduce heat transfer into the aluminum heads and piston tops, increasing thermal efficiency and allowing you to run high compression and much leaner fuel mixtures without melting the pistons or overheating.

Assemble the engine using Teflon-coated bearings and standard-tension piston rings. Purchase and install a TPI (tuned port injection) upper and lower intake manifold designed for a 1980s 305. The lower TPI manifold won't quite align with the L98 heads, so you may need to gasket-match the intake to the heads with a die-grinder. If you don't know how to port cylinder heads, have the machine shop do it for you. You may also need to slightly elongate the intake manifold bolt holes, depending upon how much material was removed during the block machining process.

Purchase a set of long-tube race headers with primaries no more than 1.5-inches in diameter and have them coated inside and out with thermally insulating ceramic powder-coating. Install a set of new, stock Chevrolet 305 fuel injectors and the associated fuel system onto the TPI lower manifold, but utilize an aftermarket fuel management unit and wide-band oxygen (O2) sensor), as well as a crank trigger or Hall effect ignition. This setup will allow you to custom tune your engine to run on an ultra-lean air/fuel ratio (as much as 20:1) when you want to save fuel, or a richer 14.7-15:1 ratio for performance or towing use.

Top off the engine with an electric water pump, an electric cooling fan, under-drive pulleys for the accessories and a cold-air intake. This combo should yield you at least 275 to 300 horsepower and 350-plus lb-ft of torque, depending on the specific tune and camshaft you use. A very mild stock-type camshaft will provide the most torque for fuel economy and ease of driveability.

Items you will need

About the Author

Richard Rowe has been writing professionally since 2007, specializing in automotive topics. He has worked as a tractor-trailer driver and mechanic, a rigger at a fire engine factory and as a race-car driver and builder. Rowe studied engineering, philosophy and American literature at Central Florida Community College.

Photo Credits

  • photo_camera chrome engine image by Thomas Czeizinger from Fotolia.com