HEADER DESIGN AND THEORY


WHY ARE EQUAL LENGTH HEADERS SUPERIOR IN DESIGN?
First of all, start thinking of your multi cylinder engine as nothing more than a number of one-cylinder engines on a common crankshaft. The goal of all multi cylinder engine builders is to make each individual cylinder produce an exactly equal amount of torque throughout a given RPM range. Any negative deviation in individual cylinder torque output has a far greater cumulative negative effect than it's individual loss alone. This is due to these single cylinder engines fighting one another, and not working in harmony. Every aspect of each individual cylinder's function must be made as close to equal as possible for maximum output. One such aspect is the overall length of the primary tubes that constitute what we commonly call exhaust headers. Because as RPM increases, the time involved in the valve opening events decreases, longer primary tubes are more efficient at lower RPM, and shorter primaries favor higher RPM. This involves energy wave timing, which is critical in the design of an exhaust header. In this particular header design, I was limited by the fact that it had to be a direct bolt on, terminating at the existing catalytic converter. However, I was still able to make the primary tubes 39 inches long from valve seat to collector. This favors midrange efficiency over top end, as this is not a high RPM racing engine. I also made sure there was ground clearance equal to the factory system as I know you guys love to lower your cars, and smashed primary tubes are notoriously inefficient. For a more in depth view on header design theory, please read the information on this other web page.
To lower production costs, it is common practice to use multiple parts that are identical. The more individually different parts there are in an assembly, the more it costs.
Honda's design considerations are biased toward the lowest production cost, and making sure the catalytic converter gets up to operating temperature very quickly for low exhaust emissions. This mandates that they use stainless steel and or cast iron as materials of choice. As you can see, there are no individual primary tubes at all in Honda's design. There are 16 individually different parts in this assembly.
In this example of a typical low cost aftermarket exhaust system the primary tubes are close to equal length, but they are far too short to be of any use for proper energy wave tuning. Although there was some consideration given to performance, as seen in the improved transition areas where multiple tubes meet, low production cost was the primary design consideration. Stainless steel is used, once again, to get the catalytic converter up to operating temperature quickly, as this is necessary for C.A.R.B. exemption. There are 16 individually different parts in this assembly.
In this example of a true equal length header set, the design considerations were biased toward maximum performance. The number of bends required to make all the primary tubes equal in length, the complexity of assembly, and all the welding required make this design relatively expensive to produce. All flanges are ground flat after welding to assure stress free, leak proof joints. This particular set of headers is a pre-production set, made of ceramic-coated mild steel, and has many more welds than the production headers will have. Stainless steel will be the material of choice in production, for the same reasons stated above. There are 28 individually different parts in this assembly. I hope all this helps in your understanding of the subject. We all need understanding to make well-informed choices.