MM: What about late-model Mustangs?
DL: Late-model Mustangs pose some concerns due to emission laws. In many cases, headers need to be compliant. JBA Headers was the original for catalyst-forward headers that met tough emission standards. The Cat4ward Shorty headers from JBA and Doug's Shortys will accommodate all original equipment emission controls while offering noticeable power increases. Most of these applications carry a California Air Resources Board E.O. number for legal use on street-driven cars. Additionally, JBA offers H and crossover exhaust systems that compliment the headers for better flow and a terrific musclecar sound. Long-tube headers designed for racing use, including engine swaps, are also available for late-model Mustangs.
MM: We see all kinds of header sizes. How do you choose the right size and type?
DL: A change in tubing diameter and length alters the power band. This can get rather involved and there are many variables that determine optimum diameter. Rule of thumb is that you want to use the smallest diameter that will not hinder high rpm flow. Smaller diameter helps keep exhaust velocities high and that is where the largest improvements will be seen in terms of torque, which is what you want on the street. Bigger is not always better when it comes to headers, especially when low to mid-range torque is important.
Larger, more radical engines will require larger diameter primary tubes right off the ports. For most street-driven small-blocks in classic Mustangs, a 1 5/8-inch to 1 3/4-inch header tube is optimum while big-block and Cleveland cars can use anywhere from 1 3/4- to 2-inches. For the late-model crowd, shorty replacement styles will be 1 5/8-inch for both the 5.0L small-block and 4.6L SOHC/DOHC cars. Long tubes will run between 1 5/8- and 1 3/4-inches.
MM: What about header coatings-painted versus ceramic?
DL: All three PerTronix Exhaust brands offer Metallic Ceramic Thermal Barrier Coating, which offers a couple of advantages over painted or raw steel headers. As the name suggests, this coating is a ceramic material that creates a thermal barrier. It holds more heat inside the header, which helps keep exhaust velocities high, which in turn improves performance. Additionally, it lowers underhood temperatures, creating a cooler intake charge to produce more power. As a side benefit, the coating increases corrosion resistance for longer header life while at the same time offering a much better looking and more durable finish than paint or raw metal. JBA headers are made of stainless steel, which naturally resists corrosion. The optional MCTBC coating on these headers does increase life while adding heat barrier advantages.
Common Header Installation Mistakes
1. Improper flange bolt torque-too loose or too tight
2. Primary tubes too large or too small
3. Collector size too large or too small
4. Header contact with body
5. Incorrect fasteners
6. Choosing long-tube headers that don't fit well with the underbody
7. Installing drag racing headers on a street car-typically too long and they hang too low
8. Headers that interfere with clutch equalizer shaft
9. Not installing a power steering ram header spacer/extension. Nearly all header manufacturers sell them.