I have 2 Demon Supercharger Carbs 850cfm. They are in good condition and work great. They were on a pair of 502s with 177 weiend superchargers. Engines made 640 hp on the dyno. This is not a duel carb set up its for two motors. They have manifold refrenced power valves that gives you extra fuel upon boost. They are 4150 pattern and I will sell the set for $475. Any questions email or call. 856-228-4744 Thanks, Jeff at J&J Marine.