The Chevrolet small-block 350 is one of the most prolific engines ever built, powering everything from pickup trucks to muscle cars. Its combination of availability, affordability, and aftermarket support makes it the ideal platform for a performance build. For many enthusiasts, the goal is a reliable 400 horsepower at the flywheel. While bolt-on parts like intake manifolds, headers, and camshafts can get you close, the surest path to a genuine 400-horsepower street engine is increasing displacement. A stroker kit, especially one from Scat Enterprises, offers the most cost-effective and straightforward way to transform your 350 into a torque-monster 383 or even a 400 cubic inch powerplant.

Understanding Stroker Kits

A stroker kit increases engine displacement by lengthening the stroke of the crankshaft while retaining the existing cylinder bore or making minor overbores. In simple terms, the pistons travel farther up and down in the cylinder, drawing in a larger volume of air and fuel mixture. This additional displacement directly translates to more torque and horsepower across the entire rpm range. For the Chevy 350, the most common stroker combination is the 383 (3.750-inch stroke with a 4.030-inch bore), which adds 33 cubic inches over the stock 350. A less common but more aggressive option is the 400 stroker kit, which uses a 3.875-inch stroke or larger with a 4.060-inch bore to reach 400 cubic inches.

How Stroker Kits Increase Displacement

An engine’s displacement is calculated by cylinder bore area times piston stroke times the number of cylinders. A stroker kit increases the stroke by using a new crankshaft with an offset rod journal. This means the centerline of the connecting rod is moved further from the centerline of the crankshaft main journal. The result is a longer piston travel. Because the engine still fits within the same block dimensions, the entire rotating assembly must be carefully balanced and sometimes clearanced (material removed from the block) to accommodate the longer stroke. The stock 350 crank has a 3.48-inch stroke; a 383 uses a 3.75-inch stroke, while a 400-inch build uses a 3.875- or 4.00-inch stroke depending on the kit.

Key Components of a Stroker Kit

A complete Scat stroker kit includes the crankshaft, connecting rods, pistons, piston rings, and often the necessary bearings. Some kits even include a flexplate or flywheel. The components are matched and pre-balanced for a specific stroke and rod length, making installation more straightforward than selecting individual parts. Scat uses high-strength cast or forged crankshafts with a radiused fillet and counterweight design to reduce vibration. The connecting rods are typically made from forged 4340 steel, heat-treated and shot-peened for durability. Pistons are often forged 2618 or 4032 aluminum alloy, designed to handle high cylinder pressures and withstand detonation. Together, these components create a rotating assembly that can safely rev to 6,000+ rpm and handle over 400 horsepower.

Why Choose Scat Enterprises

Scat Enterprises has been manufacturing performance engine components for decades. Their reputation is built on precision machining, high-quality materials, and consistent production quality. Scat crankshafts are produced in their own foundry using advanced metallurgy, and each part is magnafluxed and dimensionally inspected before shipping. The company offers both cast and forged crankshafts at different price points, making them accessible to a wide range of builders. Furthermore, Scat provides detailed technical specifications and instructions, and their customer service is known for helping builders select the correct balancing specifications. Many professional engine builders trust Scat as a cost-effective alternative to expensive custom crankshafts while still delivering reliable performance.

Scat Stroker Kit Options for the Chevy 350

Choosing the right Scat kit depends on your horsepower goal, budget, and intended use. The following are the three most popular options for building a 400-horsepower Chevy 350.

Scat 383 Stroker Kit

The Scat 383 kit is by far the most common upgrade for the 350 block. It uses a 3.750-inch stroke forged 4340 crankshaft and 5.7-inch or 6.0-inch connecting rods. The pistons are sized for a 4.030-inch bore (0.030 over stock) to achieve exactly 383 cubic inches. This kit is well suited for street rods, muscle cars, and daily drivers. With the right camshaft and cylinder heads, a 383 can easily produce 400 horsepower and over 450 lb-ft of torque while retaining good street manners. The 5.7-inch rod version is more affordable, while the 6.0-inch rod “rod ratio” option reduces side loading on the cylinder walls and can improve high-rpm performance.

Scat 400 Stroker Kit

For builders willing to do more extensive machining, the Scat 400 kit offers an even larger displacement. This kit typically uses a 3.875-inch stroke crankshaft and requires a block that can be bored to 4.060 inches (or more). The 400 stroker delivers immense low-end torque, capable of over 500 lb-ft even with mild cam timing. Because of the increased stroke, additional block clearancing is necessary, especially near the camshaft and the bottom of the cylinder bores. The Scat 400 kit is a favorite for truck applications and heavy-bodied cars where maximum grunt is desired. It can easily produce 400 horsepower with a mild cam and good heads.

Scat Pro Stock Series

Scat also offers Pro Stock series kits that use billet or premium forged crankshafts and ultra-light connecting rods. These kits are designed for high-RPM racing applications, but a Pro Stock 383 or 400 kit can also be used for a high-horsepower street build. The Pro Stock components are lighter and stronger, contributing to faster throttle response and increased rev capability. However, they are more expensive and may be overkill for a 400-horsepower street engine. Most builders will find the standard Scat forged kit more than adequate.

Component Breakdown and Selection Considerations

Crankshaft – Cast vs Forged

Scat offers both cast nodular iron and forged 4340 steel crankshafts. For a 400-horsepower street engine that sees limited high-rpm use, a cast crank is often sufficient. It will handle the power and provide a cost saving. However, for builds that see regular abuse, detonation, or extended high-rpm operation, a forged crankshaft is the safer choice. The Scat forged cranks have a 180,000+ psi tensile strength and a fully contoured design to reduce stress risers. The stroker crankshaft also must be externally balanced or internally balanced. Scat kits typically come with the appropriate flexplate/flywheel and harmonic balancer if external balancing is required, or the crank is neutral-balanced for internal balancing.

Connecting Rods – Length and Material

Rod length affects the rod-to-stroke ratio, which influences piston acceleration and wear. For a 383, the most common lengths are 5.7 inches (stock 350 length) and 6.0 inches. The 5.7-inch rod is the drop-in option; the 6.0-inch rod requires custom pistons with a shorter compression height but provides a better rod ratio (1.60 vs. 1.52) which reduces side thrust and improves ring seal. Scat’s connecting rods are made from 4340 steel forgings, heat-treated, and feature ARP cap screws or bolts. For 400 horsepower, the standard H-beam or I-beam Scat rod is more than sufficient.

Pistons – Forged vs Hypereutectic

Piston selection is critical to achieve desired compression ratio. Scat kits typically include forged pistons. For a 400-horsepower engine, a compression ratio between 9.5:1 and 10.5:1 works well with pump gas (92-93 octane). The forged pistons can handle higher cylinder pressures and are more resistant to detonation than cast hypereutectic pistons. However, forged pistons require slightly more piston-to-wall clearance, which can cause piston slap when the engine is cold. This is normal and not harmful. Many street builders choose Scat’s hypereutectic piston kits for lower cost and quieter operation, as long as compression and timing are kept sensible.

Piston Rings and Bearings

Scat kits include high-quality moly or chrome moly piston rings, precision gapped for the intended bore size. Bearings are typically included from Clevite or King, featuring tri-metal construction for durability. When installing, proper ring end gap must be verified to avoid breakage under high heat. For a 400-horsepower street engine, standard gap specifications are adequate, but if you plan on using nitrous or forced induction, widening the gaps is prudent.

Pre-Installation Considerations

Engine Block Preparation and Machining

Before installing any stroker kit, the engine block must be thoroughly cleaned and inspected. Cracks in the main webbing or cylinder walls will ruin a build. The block should be align-honed to ensure the main bearing bores are straight and round. Then the cylinders are bored and honed to the specified piston diameter (usually 0.030-inch over for a 383). Because the longer stroke can cause the connecting rod bolts to contact the bottom of the cylinder bores or the camshaft, the block must be clearanced. This involves grinding small sections of the block near the cam tunnel and the bottom of the bores. Many machine shops are familiar with 383 and 400 clearancing. Do not skip this step.

Balancing the Rotating Assembly

Even though Scat kits are pre-balanced, it is advisable to have the entire assembly balanced by a reputable machine shop using a balancer. The crankshaft, rods, pistons, rings, bearings, harmonic balancer, and flexplate or flywheel should all be included. A properly balanced engine reduces vibration, extends bearing life, and allows higher rev limits. For a 400-horsepower build, balancing is not optional.

Required Support Modifications

A stroker engine needs adequate airflow, fuel delivery, and cooling. The cylinder heads must be able to flow enough air to support 400 horsepower. Stock 76cc heads will choke a 383; consider aftermarket heads like the popular AFR or Dart SHP series with 180-195cc runners. Camshaft selection is also critical – a cam with around 220-230 degrees of duration at 0.050-inch lift and 0.480-0.520-inch lift works well. The induction system should include a 650-750 cfm carburetor (or equivalent EFI) and a proper intake manifold like a Performer RPM or Air-Gap. Exhaust must be free-flowing; long-tube headers and a 2.5-inch to 3-inch exhaust system help the engine breathe. Finally, ensure the cooling system is up to the task – a high-flow water pump and a large radiator are recommended.

Step-by-Step Installation Guide

Engine Removal and Disassembly

Remove the engine from the vehicle, disconnect all ancillaries, and place it on a stand. Remove the intake manifold, cylinder heads, oil pan, timing cover, front cover, and the original rotating assembly. Keep all fasteners organized.

Block Machining and Cleaning

Take the bare block to a machine shop for cleaning, magnflux inspection, bore honing, and clearancing for the stroker crank. After machining, thoroughly wash the block with hot soapy water and compressed air to remove all metal shavings and debris. Oil the cylinders immediately to prevent rust.

Crankshaft Installation

Install new main bearings in the block and main caps. Lubricate the bearings with assembly lube. Carefully lower the Scat crankshaft into place. Apply assembly lube to the thrust surfaces. Install the main caps with the correct bolts and torque to the specified sequence and torque value (typically 65-70 ft-lbs for a stock block with aftermarket bolts, but follow your kit’s instructions). Verify crankshaft end play (0.003-0.007 inch).

Rod and Piston Installation

Assemble the pistons onto the connecting rods using the correct pin orientation (often a notch facing forward). Install piston rings with gaps staggered. Compress the rings with a ring compressor, then gently tap the piston assembly into the bore using a hammer handle. Guide the rod over the crank journal. Install rod bearings and caps, then torque the rod bolts to specification (often 50-55 ft-lbs with ARP bolts). Check side clearance of the rods on the crank.

Final Assembly and Torque Specifications

Once the rotating assembly is installed, install the timing set, oil pump, oil pan (with new gasket), timing cover, and harmonic balancer. Use a new front seal. Install the cylinder heads, lifters, pushrods, rocker arms, and valvetrain. Torque the head bolts in sequence (typically 65-70 ft-lbs for small-block Chevy). Set valve lash according to camshaft manufacturer specs. Install the intake manifold and carburetor/EFI, then complete with exhaust manifolds or headers. Recheck all fasteners one final time.

Tuning for 400 Horsepower

Carburetor or EFI Selection

A 400-horsepower 383 or 400 needs approximately 650-750 cfm of airflow. A vacuum-secondary Holley 750 or an Edelbrock AVS 2 are good choices. If using EFI, a system like Holley Sniper or FiTech provides precise control and drivability. Ensure the fuel pump delivers adequate pressure and volume (at least 6 psi for carburetor, 58 psi for EFI).

Ignition Timing and Camshaft Considerations

Initial timing should be set around 10-14 degrees BTDC, with total timing around 34-36 degrees BTDC at 3,500 rpm. Use a vacuum advance canister that delivers 10-15 degrees of advance at cruise. The camshaft choice strongly influences power. A hydraulic flat tappet or roller cam with 220-230 degrees duration at 0.050-inch lift and a lobe separation angle of 110-112 degrees will produce peak torque in the 3,000-5,000 rpm range and peak horsepower around 5,500 rpm. For more aggressive builds, a roller cam with 240 degrees duration will push the peak closer to 6,000 rpm but will sacrifice low-end torque.

Dyno Tuning and Air/Fuel Ratios

Professional dyno tuning is the best investment after a stroker build. A dyno session will optimize the jetting, timing curve, and even cam timing if adjustable gears are used. Aim for an air/fuel ratio of 12.5-13.0 at wide open throttle, and 14.7 at idle. Advanced tuning options include using a wideband O2 sensor and data logger.

Expected Results and Performance Gains

A properly built 383 or 400 with Scat components, quality heads, a suitable cam, and good induction should exceed 400 horsepower easily. Typical dyno numbers for a 383 with iron heads (like Vortec) are around 380-420 horsepower, while aluminum heads can push that to 430-460 horsepower. Torque often exceeds 450 lb-ft, with a broad flat curve from 2,500 to 5,500 rpm. The result is a car that feels extremely responsive at part throttle and pulls hard to redline. Fuel economy is generally slightly worse than a stock 350, but the increased torque allows for higher gearing, potentially offsetting the loss in city driving.

Common Mistakes to Avoid

One common mistake is neglecting block clearancing. Installing a stroker crank without proper grinding can result in catastrophic contact. Another is using incorrect piston deck height – make sure the pistons sit slightly below the deck (0.005-0.020 inch) to avoid quench issues. Using a heavy damper without balancing is also a frequent error. Lastly, don’t reuse the old oil pump – always install a high-volume pump with a new pickup and shaft. Failure to upgrade valve springs for the camshaft is another pitfall; cheap springs can break and ruin the engine. Take the time to select quality components and follow Scat’s instruction sheet precisely.

Conclusion

Boosting your Chevy 350 to 400 horsepower with a Scat stroker kit is a proven and rewarding project. The Scat 383 kit is the most popular and best value, delivering impressive torque without breaking the bank. The Scat 400 kit provides even more displacement for those who need maximum grunt. With careful block preparation, proper balancing, and thoughtful component selection for cylinder heads and camshaft, you can build a reliable engine that outperforms many modern V8s. Whether you are restoring a classic or upgrading a weekend warrior, the stroker approach offers the most satisfying power increase. Research your options online at Scat Enterprises, consult with a reputable machine shop, and enjoy the process of building a high-performance Chevy small block that will deliver smiles for years to come.