Intake manifold, heat crossover.

No matter the argument, some people will never agree that blocking the cross over is a good thing. Leaving it unblocked does not one single thing for performance. It's all about cold weather fuel mixing and cold weather driveability and wait for it..........EMISSIONS. As long as you give the engine time enough to warm up, it will run fine, even in the coldest climates with the exhaust cross over blocked, plus, the proof is THERE regarding performance from keeping the mixture cooler, even when the engine reaches operating temperature. There's zero reason to leave the cross over open, unless you're running a stone stock engine and even then it will show benefits from blocking it off. You will simply not have the faster warm up when the engine is cold and in cold weather. Big whoop.