For most Small Block Chevy (SBC) header installations, the standard mounting hardware is 3/8-16 bolts, typically about 1.5 to 2 inches long, and made of Grade 8 steel or stainless steel. Always verify the exact size with your header kit and head design, as variations exist between manufacturers.
Common hardware specs you are likely to encounter
The following details cover typical SBC header bolt sizing, including diameter, thread pitch, length, and materials. Exact choices can vary by header design and engine head style.
- Diameter: 3/8 inch (0.375 in)
- Thread pitch: 16 threads per inch (3/8-16 UNC)
- Length: commonly 1.25 to 2 inches, depending on flange thickness and gasket type
- Material: Grade 8 steel is standard; stainless steel is common for corrosion resistance
- Finish: zinc or black oxide; anti-seize compound is often recommended, especially with aluminum heads
- Common bolt count: typical SBC header setups use multiple bolts along the flange (often eight total for a complete header pair), with four bolts per flange being a common arrangement
- Variations: some high-performance or aluminum-head applications may use 7/16-14 or even 1/2-inch fasteners; always follow the header manufacturer’s spec
In practice, the exact length and count depend on the header design, the flange thickness, and the gasket stack. If in doubt, measure the flange and gasket thickness and compare to the kit’s requirements to avoid bottoming or insufficient clamping.
Installation tips and torque guidelines
Proper installation ensures a leak-free seal and avoids head thread damage. Use the following guidelines as a baseline, but always cite your header maker’s torque specifications.
- Apply anti-seize to the bolt threads to ease future removal and prevent galling, particularly with stainless or aluminum components
- Torque in a crisscross or star pattern to promote even pressure across the gasket
- Target torque typically ranges from 20 to 25 ft-lbs for 3/8-16 bolts; adjust if the header kit specifies a different value
- Avoid over-tightening to prevent thread stripping in the cylinder head; re-torque after the first heat cycle or a short run if the kit advises
- If using studs and nuts instead of bolts, install per the kit’s torque spec and ensure proper locking provisions
Remember that aluminum heads, thick gaskets, or unique flange designs can shift the required torque. Refer to the header manufacturer for exact numbers and any special installation notes.
Summary
For most SBC header installations, expect 3/8-16 bolts in the 1.5–2 inch length range, typically Grade 8 or stainless, with a torque target around 20–25 ft-lbs. Always confirm with the specific header kit you’re using, account for gasket thickness, and follow a proper tightening sequence to ensure a solid, leak-free seal.