Sierra 18-1997-1 Cast Iron Exhaust Manifold - Fits OMC, Pleasurecraft GM & Volvo 283-350 CID Engines, Replaces GLM 56230

The Sierra 18-1997-1 is a cast iron exhaust manifold built for marine inboard and sterndrive engines that route exhaust through a center riser configuration. As the manifold carries hot exhaust gases away from the engine block and up to the riser, it has to hold up to constant heat cycling and marine moisture without cracking or corroding at the mounting flange, which is why Sierra builds this manifold from cast iron rather than lighter stamped alternatives. This manifold is designed as a direct fit for OMC 283, 305, 307 and 350 CID engines built between 1968 and 1980, Pleasurecraft GM 283, 305, 307 and 350 CID engines, and Volvo 307 and 350 CID engines, covering a wide range of small-block V8 marine powerplants that share this exhaust manifold bolt pattern and riser interface. It is finished in white and is sold as a standalone manifold, so it pairs with the matching riser, mounting kit, and gasket set for a complete exhaust rebuild rather than including those components itself. Boat owners typically replace an exhaust manifold like the 18-1997-1 when the original has cracked, rusted through, or is leaking exhaust or water due to age and salt/fresh water exposure. Because it is manufactured to the same form, fit, and function as the original equipment manifold it replaces, it bolts up using the existing mounting hardware and gasket set without modification.

Specifications

• Brand: Sierra
• Manufacturer Part Number: 18-1997-1
• Product Type: Exhaust Manifold
• Material: Cast Iron
• Color/Finish: White
• Fit Type: Universal Fit
• Weight: 36.2 pounds
• UPC: 808282243333
• OEM Cross Reference: GLM 56230, Mallory 9-40110, Osco 994

Fitment

• OMC 283, 305, 307 & 350 CID engines, 1968-1980
• Pleasurecraft GM 283, 305, 307 & 350 CID engines
• Volvo 307 & 350 CID engines

Replaces (OEM)

• GLM 56230
• Mallory 9-40110
• Osco 994

Frequently Asked Questions

What engines does the Sierra 18-1997-1 exhaust manifold fit? The Sierra 18-1997-1 fits OMC 283, 305, 307 and 350 CID engines built from 1968 to 1980, Pleasurecraft GM 283, 305, 307 and 350 CID engines, and Volvo 307 and 350 CID engines.

Is the 18-1997-1 manifold the same as GLM 56230 or Mallory 9-40110? Yes, the Sierra 18-1997-1 exhaust manifold is interchangeable with GLM 56230, Mallory 9-40110, and Osco 994, so any of those part numbers point to the same fit and function.

What material is this exhaust manifold made from? It is cast iron, chosen for its ability to withstand the heat cycling and corrosion exposure of a marine exhaust system over years of use.

Does the 18-1997-1 come with mounting hardware or gaskets? No, the Sierra 18-1997-1 is sold as the manifold only; a matching riser, mounting kit, and gasket set are needed separately to complete an exhaust rebuild.

How much does the Sierra 18-1997-1 manifold weigh? This cast iron exhaust manifold weighs 36.2 pounds.

What color is the Sierra 18-1997-1 manifold? The manifold has a white finish.

Why would I need to replace an exhaust manifold like the 18-1997-1? A center riser manifold such as the 18-1997-1 typically gets replaced when the original cast iron manifold has cracked, corroded, or developed an exhaust or water leak from age and water exposure, since these manifolds see constant heat and moisture cycling.

Is the Sierra 18-1997-1 a genuine OEM part or an aftermarket replacement? The 18-1997-1 is a Sierra manifold manufactured to match the fit, form, and function of the original equipment manifold it replaces on OMC, Pleasurecraft GM, and Volvo small-block engines.

Can this manifold be used on both OMC and Volvo powered boats? Yes, the same Sierra 18-1997-1 manifold is designed to fit OMC 283-350 CID engines (1968-1980), Pleasurecraft GM 283-350 CID engines, and Volvo 307 and 350 CID engines.

What is the manufacturer part number for this exhaust manifold? The manufacturer part number is 18-1997-1, made by Sierra.

Does the Sierra 18-1997-1 require a specific gasket set? The manifold works with the exhaust gaskets and mounting kits designed for its riser interface; consult your engine's exhaust system parts to match the correct gasket set for the 18-1997-1.