Header Performance Guide For Mustangs
Choosing The Right Headers For Your Mustang Requires An Understanding Of What Header Design Does For Performance
Headers and exhaust systems have become something of a cliché because everyone talks about them, yet not enough of us know how to choose them. We select headers for all kinds of reasons, many of them having nothing to do with performance. These days, it's more about how they look against a cylinder head and valve cover versus how they perform.
And contrary to what you might believe, headers don't always improve performance. Sometimes, they hinder depending on design. If you're running the same headers on your 427W stroker that you had on the 351W it replaced, you don't have enough header. You need larger header tubes and collectors to handle the increased exhaust gas volume. By the same token, header tubes that are too large will rob you of torque because there needs to be back pressure to make torque depending on valve overlap.
Another important element to header design, aside from performance and good looks, is how they fit. You want an exhaust header that cannot be seen hanging below the car when you look at a side profile of your Mustang. Headers that scrape speed bumps are a bad idea. If you're building a weekend racer, low hanging collectors aren't as critical. For street use, it becomes annoying every time you broach a parking lot.
When you think of PerTronix, you think of innovative ignition systems and ignition retrofits for classic Mustangs. However, PerTronix also has its own header brand, Patriot Headers, and they have acquired a couple of reputable exhaust manufacturers in recent years-JBA Headers and Doug's Headers, which has been around since 1958 and trusted by untold thousands of enthusiasts, including Shelby American in the 1960s.
We spoke with Don Lindfors at PerTronix Performance Products Exhaust Group about choosing headers for Mustangs.
MM: What kind of header do you recommend for classic Mustangs?
DL: The first question you need to ask is why you want headers in the first place. Are you looking to improve mileage or increase power? Do you have a high-performance engine that needs increased exhaust flow, a different sound, etc.? The next thing is the intended use of the car. Is it a daily-driver, a full-blown racer, a street/strip car, or a lowered Pro Touring-type car. With these questions answered, you can make an educated decision as to what best fits your needs. We look at classic Mustangs separately from late-model Mustangs because there are some very important differences, including the fact that in most states classic Mustangs are exempt from emission laws so you don't have to be concerned with that.
The PerTronix Exhaust Group offers several different types of headers for classic Mustangs. Shorty headers improve performance with excellent ground clearance and are a great way to go for lowered cars and stock or mild engines. Long-tube Tri-Y headers were pretty much invented for Mustangs, and Doug's Headers was one of the first in this segment. Tri-Ys offer big boosts in power across the RPM range and slightly better ground clearance than a traditional four-tube header, plus Carroll Shelby used Tri-Ys on his legendary GT350s. Four-tube, full-length headers are the most common type of header. They make big horsepower gains including at high RPM, but they usually sacrifice ground clearance. There are also specialty headers for engine swaps in classic Mustangs.
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.