World Products Merlin IV Block - Engine Builder Magazine

World Products Merlin IV Block

World Products has completely redesigned and re-tooled the famed Merlin Big Block to achieve new heights in performance and ease of use for engine builders and racers.

World Products has completely redesigned and re-tooled the famed Merlin Big Block to achieve new heights in performance and ease of use for engine builders and racers. Starting with all new foundry tooling and machining fixtures, World has made improvements to virtually every area of the new Merlin IV with the goal of producing a technologically advanced and top-performing iron BBC block.

New features include thicker main webs for increased strength and thicker cylinder walls, which are nominally .310″ @ 4.600″ bore. In addition to the standard BBC 9.800″ and 10.200″ deck heights, new are deck heights measuring 9.500″, 9.850″ and 10.250″. These allow greater versatility for specific engine combinations. Head bolt holes are blind on all available deck heights and deck thickness is nominally .600″.

The Merlin IV is available with a 2.120″ journal for standard BBC cam and standard .842″ lifter bores, or with a 2.283″ journal for a 55mm Babbitt cam and .904″ lifter bores. Cam journals up to 2.480″ or 60mm Babbitt and 1.060″ lifter bores can be accommodated, but are not stocked by World Products. World also has increased the volume in the priority main oiling system and added a front oil feed for dry sump systems, and relocated the lifter oil feeds and restrictor provisions to the front of the block.

The new block features siamese cylinder bores in 4.245″, 4.495″ or 4.595″ which finish at 4.250″, 4.500″ and 4.600″ respectively. Water jackets have been further enlarged for better cooling capacity. Nodular iron or 1045 billet steel 4-bolt main caps are standard and feature dual register to prevent cap walk. High strength 1/2″ ARP fasteners are employed to secure the main caps, with bolts used on the nodular caps and studs for the billet caps.

Cast and machined in ISO 9000 certified facilities, the Merlin IV is 100% American made and subject to stringent quality assurance procedures to ensure superior quality and performance. This new block is sure be a favorite among racers and professional engine builders.

For more information: 877-630-6651 or

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