How to Build a 377 Stroker 350 Chevy Small Blockby Moss Strohem
The small block Chevrolet engine has components that interchange readily among different versions and displacements. One combination is to install a 350ci engine crankshaft in a 400ci engine block, which is overbored .030 inch. The 400ci bore (now 4.155 inches) and the 350 stroke (3.48 inches) yields a displacement of 377ci. This engine has been successfully used in high performance racing applications since the late 1970s. However, it is not a direct bolt-in interchange. The main journals of the 350 crank have an outside diameter of 2.45 inches while the 400ci main bearing bores have an inside diameter of 2.65 inches. Unless an aftermarket crankshaft is used, spacers are required to allow the standard crank to fit the block correctly.
Sourcing Parts, Machining and Assembly
Locate a suitable core 400ci engine block or core engine assembly. Have a machine shop prepare (blueprint) it to required tolerances with attention to proper dimensions, including those of the main bores, block deck and cylinder bores.
Order all sub-assemblies such as the pistons, connecting rods, crankshaft (if using an aftermarket crank), cylinder heads and new fasteners (rod and main cap bolts/studs), etc. Include the main bearing spacers for the crankshaft along with the main and rod bearings, piston rings, and gasket sets in your list. If using an aftermarket crank machined to the 400 block main bore specs, the spacers are not required.
Deliver the cylinder heads to a reputable cylinder head specialty machinist--if different from the one prepping the block--for cleaning, testing for cracks and machining of valve seats and valves. If the cylinder head ports are going to be modified for improved airflow characteristics, this should be performed before the final seat work and assembly. Your cylinder head machinist will be able to give a specific recommendation as to the induction system and camshaft to use.
Contact your preferred camshaft manufacturer to order the camshaft, lifters and valve springs, along with other required valvetrain components for the intended application. Be specific in the details you provide regarding the complete car and engine combination. Once all machining has been completed and you have received all the parts, you are ready to assemble the engine.
Mount the engine block to the engine stand and organize all engine components for assembly. Test assemble the engine short block. Carefully follow all assembly instructions, procedures and torque values. Measure all clearances and check for interference or binding. Stop assembly if any binding is noticed, identify the cause and remedy the issue. Once the short block assembly is completed, install the cylinder heads and remaining components according to manufacturer’s specifications.
Install the oil pan, timing cover and other sheet metal at the last stage of assembly, taking care to be sure that nothing was overlooked or omitted and that nothing was left inside unintentionally (such as tools or miscellaneous parts).
- One other possible bore stroke combination for a 377ci engine is to use the 400ci crankshaft (3.75 inch stroke) in a standard bore 350ci block (4 inches). However, this can be achieved only with the standard bore. Not many engine blocks that are machined for performance applications are available in the standard bore unless they are new. A .030 overbore with this crank/block combination yields 383ci.
- Proper clearances and fastener torque values are very important. Be sure to follow all the recommended values and procedures for any engine build to avoid serious damage.