Sierra Exhaust Manifold 18-1986-2, Replaces OE 3857723, Fits GM Small Block V8 305-350 cid

The Sierra Exhaust Manifold 18-1986-2 is a cast iron marine exhaust manifold engineered for GM Small Block V8 engines in the 305 to 350 cubic inch range, a common power plant configuration in stern-drive and inboard boat applications. Exhaust manifolds route hot exhaust gases away from the engine block while providing the water-jacketed cooling passages marine engines require to keep exhaust components safe to operate near fuel, bilge, and crew areas. This manifold is built to meet or exceed the performance of the original equipment part it replaces, using cast iron construction for the strength and heat tolerance the marine exhaust environment demands.

This manifold pairs with the corresponding manifold gasket and mounting kit for a complete installation, so buyers replacing an aging or cracked manifold can source the matching hardware at the same time. It is designed as a direct fit for GM Small Block V8 305-350 cid engines, making it a straightforward swap for boat owners maintaining stern-drive and inboard exhaust systems.

Specifications

• Brand: Sierra
• Manufacturer Part Number: 18-1986-2
• Product Type: Exhaust Manifold
• Material: Cast Iron
• Engine Application: GM Small Block V8 305-350 cu in
• OEM Cross Reference: 3857723
• Compatible Manifold Gasket: 18-2949
• Compatible Mounting Kit: 18-8502
• Weight: 40.1 pounds
• UPC: 808282391232

Fitment

• GM Small Block V8, 305-350 cubic inch engines

Replaces (OEM)

• 3857723

Frequently Asked Questions

What engines does the Sierra 18-1986-2 exhaust manifold fit? The 18-1986-2 manifold is built for GM Small Block V8 engines in the 305 to 350 cubic inch range, a common configuration in stern-drive and inboard marine engines.

What OEM part number does this manifold cross-reference? It cross-references OEM number 3857723, so if your original manifold carries that number, the 18-1986-2 is a direct equivalent.

How much does the 18-1986-2 manifold weigh? This exhaust manifold weighs 40.1 pounds.

What is the manifold made of? The 18-1986-2 is made of cast iron, chosen for its strength and heat resistance in the marine exhaust environment.

Do I need a separate gasket to install this manifold? Yes, the 18-1986-2 manifold is installed with manifold gasket 18-2949, which is sold separately.

Is a mounting kit required for installation? Installation uses mounting kit 18-8502 alongside the 18-1986-2 manifold and its gasket.

Is this a genuine Sierra part or an aftermarket copy? The 18-1986-2 is a genuine Sierra manifold engineered to meet or exceed the original equipment part it replaces.

What comes in the box with this manifold? The package includes the 18-1986-2 cast iron exhaust manifold; the manifold gasket (18-2949) and mounting kit (18-8502) are separate items.

Will this manifold work with other engine sizes besides 305-350 cid? The 18-1986-2 is specified for GM Small Block V8 engines in the 305 to 350 cubic inch range; it is not listed for other displacements.

Why would I need to replace my exhaust manifold? Marine exhaust manifolds like the 18-1986-2 are commonly replaced when the original develops cracks, corrosion, or coolant leaks from age and constant heat cycling.