small block Chevy V8 engine

(Image/Curbside Classic)

You’ve got questions, we’ve got answers. We work with the Summit Racing tech department to help you tackle your auto-related conundrums. In this week’s Mailbag, we’re recommending a drivetrain combo to breathe more energy and efficiency into a tired old 350 small block V8 engine.

Q: I have a 1972 Impala with a tired 350 engine, Turbo Hydra-Matic 350 transmission, and 2.73 rear axle gears. I need a recipe for a fuel-efficient drivetrain combination for this car. I want to keep it carbureted, if possible. What would you recommend?

A: You used the word right there in the question—“efficient.” Efficient engines operate efficiently, so here’s a tried-and-true recipe for building one.

Start by building the bottom end of the engine, paying close attention to assembly tolerances. You want to keep them on the tight side. We suggest using hypereutectic pistons because of their tighter piston-to-cylinder-wall clearances. Keep the compression ratio around 9.0:1.

For a camshaft, we recommend a COMP Cams hydraulic cam. With 203/212 degrees duration at .050 and .421/.451 inches of lift, it’s designed to deliver good low-end torque and gas mileage. We also recommend a set of Trick Flow 23-degree aluminum heads. They can tolerate more compression than iron heads, making the engine more efficient. The Trick Flow heads are also a lot lighter than iron, and the less weight you’re lugging around, the better.

An Edelbrock Performer intake manifold and 600-cfm Edelbrock Performer four-barrel carburetor will make a good induction system. You should get a calibration kit for the carburetor to fine-tune it to your engine combination.

For ignition, we recommend an MSD HEI distributor and MSD Blaster 2 ignition coil. This will give you optimum spark for more complete burning of the air/fuel mixture in the combustion chambers. A free-flowing 2¼-inch dual exhaust is a must. A set of small-tube headers would also help.

Since you are looking for maximum torque with the least amount of drivetrain loss, I would get a 700R-4 overdrive automatic transmission, a lockup torque converter, and a 3.20-3.45 rear axle gear ratio.

The name of the game for fuel economy is efficiency, and this combo is about as efficient as you can make a carbureted 350.