To stay on the leading edge of technology; an exhaust manufacturer (or fabricator) must maintain a close working relationship with top engine builders and racers. The feedback gained from these relationships is used to constantly refine the finished exhaust product.

The two key factors that have the greatest effect on exhaust flow are volume and velocity. A properly tuned exhaust header must have enough tube size to allow the correct volume of exhaust gas to pass from the engine for maximum power and the velocity must be maintained to provide maximum torque. The proper balance of these two factors will put the torque and horsepower at the most useable point in the rpm range for a particular application.

The Basics

When an exhaust valve opens, the escaping exhaust gasses create a negative pressure wave that travels at the speed of sound down the header tube. As this wave reaches the end of the header tube, it expands, causing a negative “suction” wave to travel back up the tube. When this “suction” wave reaches the cylinder, it again reverses direction heading back down the tube in the direction of the original wave.

A properly designed header is engineered to take advantage of this wave action. If the header is designed so that the negative wave reaches the cylinder as the exhaust and intake valve are both open (valve overlap), the suction created by this wave will assist in removing exhaust gas from the cylinder (scavenging).

As the exhaust is pulled out faster, the intake charge is pulled in faster resulting in better cylinder filling. This causes higher volumetric efficiency, which results in increased engine power.

Production vs. Custom Headers

It is important to understand why and how Dawson Racing Headers produces a superior custom header when compared to an average production style header. Unlike mass producers of exhaust systems, we build headers that are geared to the specific needs called for by each customer. We are not interested in taking short cuts in the design phase to ease the manufacturing process in an attempt to mass-produce headers. Performance is our primary concern.

Products that are designed with mass production in mind always sacrifice peak performance. For example, if a tube used in a header design is compromised in length so that it can be bent in one piece very quickly instead of being cut and welded, it will not require elaborate tooling or time and attention from a trained craftsman to assemble the finished product. Likewise, if a set of headers can be designed to fit a wide range of applications instead of just one, the sales numbers will be higher, requiring less work on the manufacturers part. This also limits the tube size choice for the customer, as the manufacturer has to choose the most “popular” size to build. The performance of the header is compromised, starting with the design process, to achieve these production goals.

The compromises listed above (and many others too numerous to completely list here) can produces a part for relatively small amounts of money when compared to a custom part. The greatest challenge when taking this approach is to sell enough of the product to make it worth the investment in the tools, machinery and fixtures required to enable the use of lesser skilled workers in the design and manufacturing processes.

It has been said by header manufacturers that good design is a good compromise. This approach and that described above often sacrifices the quality of the product in favor of speedy and cheap manufacture. These are not sacrifices that Dawson Racing Headers is willing to make. Our goal is to make a header (or exhaust system) with the best fit and performance that our efforts can achieve.

Current Technology

The “bigger is better” theory has almost always proven to be false, but never more so than today. The trend in today’s high rpm competition engines (Competition Eliminator and Pro Stock) is toward smaller and shorter primary tubes combined with a properly matched “venturi” (neckdown) style 4 into 1 or Tri-Y collector.

Many factors must be taken into consideration when choosing a header tube size for a particular combination. Specifics such as vehicle use (race only and what class, street and race or street only), vehicle weight, transmission type and ratios as well as rear end gearing are all factors. Engine parameters such as cubic inch displacement, intended rpm range, shift points, camshaft type (hydraulic, solid, or roller), camshaft specs (lift, duration and overlap), compression ratio, carburetion (or fuel injection) and cylinder head type and airflow all have an effect on header tube size.

Another key factor in designing a proper header is the primary tube length. As mentioned above, high rpm engines tend to respond better to shorter primary tube lengths. Conversely, lower rpm engines work better with longer primary tubes. Tube length can be an excellent tuning aid and allows the racer to shift his peak torque when necessary with the use of primary tube extensions.

The final part of the header combination is the collector. There are many types of collectors available today for the different types and uses of a header. The choice of a collector size and length should be part of an overall header design and not an afterthought. On street headers, a welded on collector is the most practical. For the bracket type racer, a slip on merged style collector is probably the best choice for value and power. For the high rpm and maximum effort engine, a merged “neckdown” style collector or a Tri-Y style collector can be the ultimate choice for maximum power. These collectors have gained wide acceptance in all of the faster classes as part of a total header combination.

As in the past, designing a header is not an exact science. It is a matter of “cut, test and try again” (an old Hooker adage). There are basic principals that always hold true, but since no two engines will react exactly the same, ongoing dyno and track testing is critical to achieve maximum performance for a specific combination.

We take all of the above listed important factors as well as current dyno and track testing information into consideration before designing and building a header for our customers. The many class and race wins as well as records are a testament to our success. Let us be part of your winning combination!

Material Choices – Mild vs. Stainless Steel

One of the biggest choices that a customer has to make is that of what materials and coatings to use on his new header. As with any other header decisions, the choice depends on the end use of the header and, of course, his budget. The two most common materials are mild and stainless steel. There are many other more exotic materials available such as Inconel and Titanium to name a few, but we will not cover those at this time. If you have questions about these exotic materials, please call.

Mild steel is an excellent choice as a header material when used in the proper applications. Most of the street and race headers today are built from mild steel and covered with a metallic ceramic coating for protection and good looks.

A mild steel header does have its drawbacks - when used in any application it has a limited lifespan. It will eventually succumb to the ravages of rust and temperature (even with today’s modern coatings). This said, it is also important to know that we have seen coated headers that have lasted for 15 years or more. The application of a Metallic Ceramic Coating will increase the life of a header and decrease under hood temperatures resulting in a slight power increase. Because the coating helps hold more heat inside the pipe and expel it out the end of the header (instead of radiate it though the tube), we have seen headers used in extreme conditions such as fuel funny car zoomies increase life from about 12 runs to as high as 20 runs.

It is important to note that a mild steel header rusts from the inside out. This is the result of high temperatures and the presence of moisture and certain acids created by the combustion process. Vehicles that sit for long periods or that do not warm up the exhaust system completely are even more prone to this. Many coating manufacturers sell an inside/outside coating service, but we have yet to see a coating that could withstand the high exhaust temperatures generated inside a header tube without eventually burning off. Also a coated header is extremely difficult to repair because the coating has to be completely removed before welding to avoid contamination.

Another issue to be addressed is the use of heat insulating wraps. We strongly discourage the use of these wraps on anything but drag race headers. These wraps hold in too much heat and over a period of time will literally “cook” the carbon out of the steel, causing it to break down and disinigrate.

The use of stainless steel in the construction of headers is usually the best choice in most cases (if the budget allows) and a necessity in some others. Stainless steel offers many advantages over mild steel – the most notable of these being ease of repair (no rust or coatings to deal with) and a virtually infinite life. They also do not require thermal barrier coatings and are not affected by thermal heat wraps.

Certain applications that generate high exhaust temperatures such as high rpm race engines and turbocharged applications almost require the use of stainless to gain longer life. Because stainless is not high in carbon like mild steel, high exhaust temperatures do not affect it. It is also denser than mild steel and because of this, it is stronger and has better heat retention, which increases the exhaust speed and gives it the potential to make more power. Because it is stronger, a header can be built out of thinner material, which makes the finished product lighter.