How to Replace a Big Block Chevy With a Small Block Chevy

Replacing a big block Chevy engine with a small block Chevy engine requires only minor changes. There is less difficulty with clearance when downsizing. The major consideration is the exhaust. The exhaust manifolds or headers will not fit a small block and will need to be replaced, or if the small block does not have an intake manifold, one will need to be purchased. The big block manifold is not interchangeable. The accessory brackets are also not interchangeable. Headers are the easiest way to connect the exhaust. The standard exhaust pipe may not fit the small block stock exhaust manifold, so it will need to be reworked or replaced.

Things You'll Need

• Floor jack
• Jack stands
• Engine hoist
• 1/2-inch drive ratchet
• Set of 1/2-inch drive sockets
• 3/8-inch drive ratchet
• Set of 3/8-inch drive sockets
• Set of wrenches
• Flat-head screwdriver
• Phillips screwdriver

Instructions

1. Drain the radiator. Remove the upper and lower radiator hoses with the flat-head screwdriver. Take the upper and lower bolts out that secure the radiator shroud, using the appropriate tool (wrench, ratchet or screwdriver, depending on the type of bolts).

2. Remove the engine fan by removing the four 13-mm bolts, using a socket. Lift the fan and shroud out of the engine compartment as a pair. Remove the radiator by removing the securing bolts, using a socket.

3. Remove the throttle cable and the transmission kickdown cable from the side of the carburetor. Remove the fuel inlet line, using a wrench. Remove the vacuum lines, including the brake booster line, from the intake manifold.

4. Disconnect the water temperature, oil pressure and distributor electrical connectors. Disconnect the negative cable from the battery, using a wrench. Disconnect the main red power wire from the back of the alternator, using a wrench. Pull the plastic electrical plug for the field wiring out of the alternator.

5. Remove the carburetor by removing the four 13-mm nuts, using a socket or wrench. Take the nut off the distributor hold-down clamp, using a wrench. Disconnect all the spark plug wires from the spark plugs and lift the distributor out of the block.

6. Remove all the bolts securing the exhaust manifolds to the engine, using a socket and ratchet. Disconnect the bottom side of the manifold by removing the exhaust-to-manifold bolts, using a socket. Lift the manifolds from the engine compartment.

7. Raise the front of the vehicle and support it on jack stands. Drain the oil from the engine.

8. Remove the torque converter cover, using a socket. Remove all the bolts securing the torque converter to the flexplate, using a wrench and the appropriate socket. Place the floor jack under the transmission oil pan and raise it enough to support the transmission. Remove all the bolts in the transmission bellhousing, using a socket and ratchet.

9. Remove the two motor mount bolts, using a wrench on one side and a socket on the other.

10. Attach the engine hoist to the engine by installing one bolt through the chain in the top front corner of the head just below the intake manifold and one bolt on the rear opposite side in the same location on the head.

11. Raise the jack enough to lift the engine clear of the frame engine mounts. Use the common screwdriver to pry the transmission away from the engine. As soon as the transmission comes loose, pull the engine slightly forward until it is clear of the transmission. Hoist the engine up enough to clear the radiator support shroud. Watch the engine as it is being raised for any wires still connected. At this point, disconnect the starter solenoid wire. Remove the engine from the vehicle.

12. Replace the small block in the exact reverse order of removal.