LSXR Rectangle Port Heads (LS3, L99, L76)LSXRRectangle Port Heads (LS3, L99, L76) FAST engineers teamed up with airflow specialists at RHS to develop polymer intake manifolds for GM LS based engines. Testing on a near stock LS7 engine with a Big Mouth 102mm Throttle Body produced gains of 16+ horsepower, and 26+ rear wheel horsepower on a 500c. i. engine. The LSXR 102mm Intake Manifold features a revolutionary new modular design that allows fast and easy disassembly and features the ability