A very common question we get is: What’s the difference between 4-1 headers and 4-2-1 headers? Which header design is better and which header makes more power?
However, it’s not a straight forward easy answer, and we’ll explain below the differences to help you decide what is best for your car, because really, the answer is- it depends.
4-1 is for high end power and 4-2-1 is for lower end. For cars with automatic transmission we always recommend 4-2-1 because your engine rpm cannot reach as high as manual. It will change gear about 7k rpm automatically for most of the car. Manual is different, you can rev until 9k rpm (depends on your car setup). When 9k rpm, a lot of exhaust gas will be generated. So, 4-1 is working well here.
4-1 has bad respond at low end because of back pressure from your muffler. Imagine your engine is running at 2-3k rpm, the pressure from outside the car is greater than your exhaust pressure generated by your engine. So, your engine will have extra burden now. You will feel more heavier to drive your car, then you will press harder on accelerator. At last, end up burn more fuel.