A few reasons why major, mass produced brands aren't well built
As headers get older, there are two areas they tend to initially fail
- One area is where the header tubes enter the header flange. Because this area is the HOTTEST part of the header and is also the area where most of the vibration stress is concentrated, the chance of the header developing a crack is at it's maximum. External brazing the tubing where it connects to the flange will counteract this, but it is a process most manufacturers ignore.
- The other area is the large or inlet end of the collector - where the header tubes enter. Most mass-produced headers that are built with collectors have ones that are swaged (or stretched) to fit over the header tubes. This means that the wall thickness of a swaged collector is considerable thinner at it's inlet or expanded end (as much as 25% thinner, depending on the amount of expansion) and is therefore, much more likely to crack or burnout in that area. A collector design that is of a consistent wall thickness, with deep creases designed to reduce exhaust gas expansion and improve turbulence control will create more power and be stronger than your conventional collector.
In depth about Equal Length design
Out of the 40 years Ed has been in business, all of his header testing and experiences has been based entirely upon the use of TRUE equal length design. A lot of companies claim equal length, TRUE equal length is defined as
all tube lengths held within +/- 1/2" of designated length. Ed has measured many company's headers (he does repair of damaged units as well, so he gets this a lot) and very seldom, he says, has he ever measured a mass-production header with less than 4" variation in tube length.
There are two major reasons why Equal Length header designes are so important.
- This is the only way to optimize performance because all of the cylinders of an engine - relative to how the header affects them - function equally. No differences in the power outputs of different cylinders because of differences in exhaust tuning and exhaust scavenging due to the header tubes having different lengths. Combined with correct tube lengths, an equal length header design maximizes power over a very wide RPM band which improves performance on both track and street.
[LIST]Varying header tube lengths often create unequal air/fuel mixture distribution problems in intake manifolds. Engines using unequal length header designs have proven that the engine sometimes will not respond to changes in carb jet sizes and/or ignition settings, may not run smoothly, may not perform better (or sometimes worse) when compared to engines running equal length designs.
In depth about Header Length
The length of a header (this includes the length of the header tubes AND the collector) has two basic effects on an engine:
- The length of the header determines at what point in the RPM range that the header "tunes" or maximizes it's effect on horsepower output. It does this by using the sound waves reflecting back and forth inside the tubes and collector to further aid in the extracting of exhaust gases from the engine's cylinder. The effect on the engine is that as the header's length decreases, the part of the RPM range where the "tuning" effect adds power increases. It should also be pointed out that if the lengths are way off (as in, too long or too short for the engine's capabilities) then the header can literally be "out of tune" and actually push exhaust gases backwards into the cylinders.
The range of useable lengths can vary considerable, relative to the RPM range of the motor and the intended use of the vehicle in concern. For example: "Pro Stock" drag cars may use headers with tube lengths as short as 24" and collector lengths basically no longer than the collector taper itself, the power to weight ratio of these cars along with the rpm range these engines run in, basically dictate header designs that only need work from 9,000 rpm and up. In contrast, most "street" vehicles as well as many competition vehicles have engines revved anywhere from 6000 to 9000 and need a header that is much longer so that the header "tunes" in the engine's actual rpm range. 98% of the time, "tuned" lengths should be no shorter than 32". On the street, where increased bottom and mid-range power is needed, the header tubes should be no shorter than 34" in length. On a Honda revving around 8000 rpms, consider a header tube between 38" and 42". Notice that mass production headers are quite often MUCH shorter than that.
- The length of a header actually represents specific volume. This volume contains a MASS (weight) of exhaust gases. While the utilization of the speed of these contained exhaust gases creates "exhaust scavenging" and, when optimized, can increase horsepower considerably, it has been proven that LONGER headers (as they contain a larger mass of exhaust gases) are quite beneficial when used on street cars as they further improve exhaust scavenging. Mass-produced headers are generally shorter in the interests of reducing costs, and a lot of times actually hurt the performance of an engine when compared to stock manifolds.