When building a Subaru WRX/STi or other popular Subaru model, many important questions will come up. While there are many to ask regarding performance, no one question has been asked as often as the debate between equal length and unequal length headers. Below you'll see some of the key ideas behind equal and unequal length headers.
UEL and EL Headers and Engine Wear
Let's look at bit into how a header works and what it does for the engine. Simply put, the header directs hot exhaust gases away from the cylinder and into the turbocharger. An equal length Subaru WRX/STi header will expell gases at an equal rate per pulse, with gas from each cylinder leaving the header at the same time. With an unequal length header, gas from the two longer runners will remain in the header as it will take longer to reach the collector.
This results in lower cylinder temperature on an equal length header, which can help prevent ringland failure. Another benefit of equal length headers is the balance of backpressure at the exhaust ports, which will improve volumetric efficency and overall top end performance.
EL and UEL Headers and Performance
Unequal Length Headers are typically lighter since shorter runners on two cylinders require less material. For those enthusiasts hoping to shed every ounce of weight from their car, this can be a huge advantage over equal length headers. Two shorter runners also means less engine RPM required to get exhaust gas to the turbo, so you'll see quicker turbo response with a car running UEL Subaru Headers. This is usually around 200-300rpms, but those few RPM's can be vital for cars that require a quick spooling turbo.
Equal Length Subaru headers will perform better at mid RPM, with slight loss at higher RPM's. This is due in large part to the design of the headers, as a 4-2-1 design is more efficient in these areas than a 4-1 design seen with UEL Subaru Headers.
UEL and EL Subaru Headers and Sound
Knowing what we already discussed about the different types of Subaru WRX/STi Headers, we can easily see how they will each sound differently. The shorter runner on a UEL header will create a louder noise than a longer runner as it has less piping to travel through. This results in the iconic Subuaru Rumble. This rumble doesnt exist on cars running an Equal Length header
Whether or not you want this sound will help you decide which header is best. Some people personally love the Boxer Rumble, while others are completely fine without it - it's all user preference!
Equal Length Headers appear to be the winner here. However, both headers will increase performance over stock, and both typically increase the sound of the exhaust. On most street driven applications, the increase in cylinder temperatures seen with a UEL Subaru header is negligible. At the end of the day, it's completely up to you the owner of the car which will be better suited for your application.