Chevy 350 Exhaust Flange Bolt Size: Specifications and Installation Guide

ByThe Answerlode Editorial Team

Chevy 350 Exhaust Flange Bolt Size: The Answer

The standard exhaust manifold bolt for a Chevy 350 small block is 3/8″-16 (3/8 inch diameter, 16 threads per inch). This applies whether your 350 is in an early truck, a Camaro, or any other vehicle—the bolt size doesn’t change. You’ll need a 9/16″ socket or wrench to install them.

Length and Specifications

Most original Chevy 350 exhaust manifold bolts are 2 1/4″ to 2 1/2″ long. Length can vary depending on the specific manifold design and whether you’re running original cast iron manifolds or aftermarket headers, so measure your old bolts or check your manifold’s specifications before ordering replacements.

The torque specification is 20–25 foot-pounds. Use this range to avoid both under-tightening (which causes exhaust leaks) and over-tightening (which can strip threads or crack the manifold). Always torque the bolts when the engine is cold, since metal expands as it heats and a hot manifold will loosen as it cools.

Installation Sequence

Tighten the bolts in a center-outward pattern, working from the middle bolts toward the ends. This distributes clamping pressure evenly across the manifold gasket and helps prevent warping or gasket failure. Use a calibrated torque wrench rather than guessing by feel—it’s the difference between a sealed manifold and an exhaust leak that’ll drive you crazy.

Finding the Right Bolts

Replacement kits for 3/8″-16 exhaust manifold bolts are widely available from automotive suppliers and online retailers. Grade 5 or Grade 8 bolts offer better durability than lower grades, and stainless steel options resist corrosion if you want longevity. Some kits include washers and gaskets; verify what you’re getting before ordering to avoid a second trip.

Troubleshooting Common Issues

If an old bolt won’t budge, apply penetrating oil and let it soak before trying again. Forcing a stuck bolt risks breaking it off inside the manifold, which turns a simple swap into a drill-out job. After installation, run the engine and listen for exhaust hissing. A leak usually means either the bolts came loose during the heat cycle or the gasket wasn’t seated properly. Re-check your torque specs after the first startup.

Before You Buy

Confirm the bolt length by comparing to your old bolts or checking the manifold’s manual. Cast iron manifolds (most common on 350s) handle standard torque specs fine. If you’re using aluminum manifolds or headers, they’re softer and may need slightly lower torque to avoid stripping threads—check the product documentation. Anti-seize compound is sometimes recommended for exhaust bolts in high-vibration or salt-air environments, but use it sparingly and only if the manufacturer suggests it, since excess can throw off your torque reading.

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