Aftermarket exhaust manifolds that increase the internal bore size of their units compared to the port size on the cylinder head cools the exhaust inside the manifold only, but, the temperatures inside the combustion chamber is higher because of less turbo boost. This has a negative effect on engine performance as it decreases turbo drive pressure energy and falsely lowers EGT readings. EGT is normally monitored by the driver to determine cylinder temperatures and by changing the base temperature referred to can result in engine damage. BDs Full Bore exhaust manifold restores exhaust flow balance, improves power and reduces EGTs inside the combustion chamber. All of which is accomplished by maintaining internal bore size thus maintaining turbo drive pressure. Get better performance and save hundreds of dollars by using BD product versus other aftermarket manifold kits. Made from high-silicon ductile iron, the Full Bore is a direct, bolt-in replacement for the factory manifold and is even drilled and tapped to accept the most popular EGT probes.