Fenderwell Headers
Although they require cutting up some sheetmetal, fenderwell headers offer packaging benefits over more conventional headers. "With fenderwell headers, there is lots of spark plug room, you don't have to worry about oil pan or starter clearance, and in most cases they are very easy to install," Lemons explains. "The drawbacks are that they require cutting your inner fenderwells and compromise tire clearance, which can limit a car's turning radius. Also, if the collectors are pointing downward, they'll blow dust on your neighbors in the pits."
Collector Length
Experimenting with collector length is a decades-old trick, but there are some simple facts to remember before tweaking away. "A longer collector will typically make more torque, while a shorter collector will typically make less torque but more top-end power," Lemons says. "If a car has a full exhaust system, it will be less sensitive to the length of the collector. With open headers, sometimes it's pretty common to use a larger collector in addition to collector extensions to fine-tune the torque requirements to launch the vehicle out of the hole."
Raw Materials
The two most common materials used in building headers are mild steel and stainless steel, each with its pros and cons. "We build headers in both materials, and the most significant difference between the two is that stainless costs about twice as much," Lemons says. "Stainless is a stronger material and won't rust, but it discolors and weighs more. Mild-steel headers that are well-coated inside and out make a lot of sense, since they're cheaper, lighter, and very durable. We use 3/8-inch-thick header and collector flanges, 18-gauge tubing, and 16-gauge collectors. Both types of metals are TIG welded."
Primary Length
Primary length definitely has an effect on the power curve, but in stock chassis cars, getting all four tubes from the flange to the collector in a normal location limits how much the length of tube can vary from one design to another. "The difference between a complicated design with many bends and a simple design with fewer bends is only a few inches, which isn't enough to significantly impact the power curve," Lemons explains. "However, having the ability to use different tube sizes allows much greater flexibility in designing a header. Smaller tubes act like longer tubes, and bigger tubes act like shorter tubes."
Bends
While a bunch of fancy bends can boost a header's intimidation factor, they're not necessarily desirable for ultimate performance. Lemons says in a perfect world, a header would only have one bend: out and back. However, the confines of a stock chassis makes this impossible. "To make things even worse, performance headers require putting too big a tube into too small a chassis and trying to get them as close to the same length as possible," he explains. "This is not an easy task. We try to keep our designs as free-flowing as possible by using as large a radius in our bends as we can in addition to keeping the tube square to the exhaust port without back-cutting the bend at the flange."