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The rectangular port MM heads are the first in the industry to offer aftermarket 12-degree cylinder heads (15-degrees is stock) for the LS engine. The 12-degree valve angle positions the valves closer to the center of the bore and further away from the cylinder walls, unshrouding the valves for more air flow-thus performance. Mast offers these heads unassembled so you can configure your valvetrain/springs to match your camshaft. Mast stocks all the components you'll need to easily assemble and install these brutes.