Building your Own Headers - Part 2

Building your Own Headers - Part 2
By O'Darrell Poole (c)

As we discussed in our first column the design characteristics of our headers fall into 4 distinct categories. To recap they are as follows

1) Primary Pipe Diameter
2) Primary pipe Length
3) Collector Diameter
4) Collector Length

While the diameter and the length of both the primary and collector pipes are of extreme importance there are other very important factors in header design. We will discuss 3 necessary elements.

1) Cylinder Head to header primary pipe entrance
Maintaining gas flow velocity is vital in proper exhaust scavenging. If your header flange is causing a partial blockage (by way of size or shape) turbulence will be step up at the time when velocities are at its highest therefore turbulence will be at its highest. If your header flange opening is to large gas velocities are slowed down and will effect the timing of the negative pressure pulse used to promote scavenging and cause the pulse to come well after TDC. To ensure proper flow from cylinder head to primary pipe use a header flange shaped to match your head (square, circle, rectangle) and merge it into your primary pipe. Using a header flange with short starter tubes that transition from your square (cyl head port) to your primary pipe ( curcular) is common practice.

2) Primary Pipe to Collector Merging
Maintaining gas velocities into and beyond the collector merge point is sometimes overlooked. The collector is not only the spot where the primary tubes merge into one but must also promote smooth transition from primary pipes to our collector pipe. The method used by some is to weld the centre section together with a small piece of metal to help reduce the dead zone left when for example four pipes meet. Another method is to bring the edges of the pipes together in the centre to form a cross where by eliminating all together the dead zone and welding them together. I prefer the ladder method as it promotes smooth transition with no dead zone.

3) True Equal Length Headers
Apparently equal length headers to some does not mean primary pipe length's that are the same length to every cylinder. We have seen headers primary pipe length vary from cylinder to cylinder by as much as 15". Our internal combustion engine is nothing more than a air pump that we put extensive time into making all the internals the same. Examples are compression ratio's, cylinder head volume, intake tract length, and camshaft lift and durations. Now no one would ever think of putting 8 different pistons in a engine or having cylinder head volumes differ by 25% or have a camshaft ground with 8 different profiles, so why would we put 8 different lengths of pipe on the exhaust side of our engine. Utilizing sound wave and pressure wave technology in our exhaust system is free power and once you have gone through the task of determining proper primary pipe length for your header and then not taking advantage of that imformation is just silly. Design your header for your RPM range then use that length on all cylinders and get equal power from all cylinders.

Stay tuned for more information on designing and building your own headers in up coming columns. We welcome your intake and exhaust system questions!!!! Contact us at autocraftdynamicdesign@live.ca O'Darrell Poole