For Post-1986 Mercruiser GM V8 Big Block -4 inch elbow -No spacer In the V8 GM Big Block, GLMs fully tuned design guides exhaust gases directly to the riser without turbulance and back pressure. This increases the engines performance. These GLM manifolds also feature an additional 30% increase in water cooling area that decreases the manifolds overall body temperature significantly. In GLMs Mercruiser replacement 4 inch riser, there are two additional water jackets. This allows a higher volume of water to flow through the riser, keeping the engine cooler. *All manifolds and risers are powdercoated black for maximum corrosion protection* **Cast Iron manifolds and risers come with a 3 year warranty**