Equipped with our performance Stainless Steel High Flow Risers, these are our best performing systems. They are a direct replacement for many stock Mercruiser manifolds in Bravo and Alpha applications with exhaust outlets in the stock location (if you have existing exhaust outlets, you should check our dimensions to determine fit before ordering). The 16" long riser on these systems is a must with High Performance camshafts to prevent reversion (water ingestion). NOTE: Engines using larger than stock, aftermarket camshafts may require a dry tailpipe system to prevent reversion. Provide us with your camshaft's lope separation angle and duration at .050" before choosing an exhaust system! These longer risers WILL NOT work with Selector systems or stock "S" pipe connections. Brackets to keep all of the stock componenets in their existing locations (shift quadrant, ignition module and oil filter bracket) are available and sold separately.EMI Thunder Exhaust Manifolds are constructed from the highest strength 356 aluminum that is heat treated to a T-6 condition after it is cast. They are then hard-coat anodized to a military specification throughout to prevent corrosion of all surfaces including the internal water passages. Lastly, EMI Thunder Exhaust come standard with a durable gloss black Fusioncoated finish. They are also available in your choice of custom Fusioncoated colors or highly polished (polished systems are not hard-coat anodized).The EMI-511 System includes 1pr. EMI Exhaust Manifolds, 1pr. High Performance Stainless Risers, Bolts, gaskets, and fittings.