A question we get a lot 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? It's not that easy of an 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. These headers are for a 4 cylinder or an 8 cylinder car, and we'll go into more detail below.
As the name implies, the headers start from 4 pipes that merge into 2 pipes and those merge into 1 pipe. You can see from the headers on the right how this design plays out. For most cars, this design produces more mid range power with the sacrifice of top end power. Mid range power is great for the street since when you drive you usually do not rev your motor close to redline. Instead, you keep the revs somewhere in the middle, usually shifting at 3-6K, and this is where the headers shine. Do note that not all 4-2-1 headers produce more mid range power at the expense of top end. Some high quality headers are able to improve top end as much as they improve the mid range. This is more the exception than the rule as most headers that are 4-2-1 do produce more power in the mid range, so the "seat of the pants" and "butt dyno" make these headers feel stronger since the power band isn't as high in the RPM range. This goes the same for both 4 cylinder and 8 cylinder applications. Since on a V8 the headers are 4 cylinder per side, you would simply have two 4-2-1 headers, one on each side.
4-1 headers are designed so that all 4 exhaust pipes merge into one. In most dyno tests, this produces the most top end power since it usually offers the best flow characteristics for the engine at high engine speeds. 4-1 headers usually move the power band up, which makes the bottom of the RPM band feel a bit weak and the "seat of the pants" feel might not be as strong as a 4-2-1 header. However, dyno tests have show that at low RPM there is very little difference in power. The 4-1 headers usually have less back-pressure than the 4-2-1 header and customers have stated their cars seem louder at high RPM with the 4-1 headers. Most headers that are street legal or CARB legal are usually of the 4-2-1 design but there are exceptions. You can see the design of the 4-1 headers in the picture on the right.
Which headers offer more ground clearance?
Since 4-2-1 headers merge into 2 pipes before they merge into one, there is usually more ground clearance here. You usually have only 2 pipes under the car instead of 4. You can see the difference in ground clearance from the pictures of the headers above. Vibrant headers offer great ground clearance with the 4-1 and 4-2-1 design.