The Confusion of Header Terminology
The questions "Are Sanderson headers direct-fit?" or "Do I need to modify my down pipes to connect to Sanderson headers?" are asked regularly, and the answers are simple.
NO, Sanderson does not manufacture direct-fit headers, and YES, you will need to modify your down pipes! But, please allow me to explain how this can be confusing for some.
This is simply a misunderstanding of terminology. We often own newer vehicles that we drive on a daily basis. We like the warranty, reliability, power and fuel efficiency that goes with all the creature comforts in a modern vehicle. We may decide to upgrade these newer vehicles. And one of the most common upgrades is to change the exhaust system by adding a cat-back kit with different mufflers, or to install headers. All vehicles since 1995 (1996 in the USA) use what is called an OBD (on-board diagnostic) system that coincides with the computer-controlled systems on the vehicle. To maintain the integrity of these systems, laws were passed to ensure the various system components were receiving accurate information to manage the proper performance and efficiency of the engine. This is a GOOD thing!
On these late model vehicles (same as vehicles of the past), upgrading the exhaust is usually the most cost-effective step to improved performance, but you do NOT want to go backwards by affecting the efficiency of the engine. Making sure you use aftermarket performance components that are designed to work on these late model vehicles is extremely important! This includes maintaining component location such as the catalytic converter, and any sensors within or near the factory exhaust. No one wants to spend hundreds (or thousands) of dollars on an exhaust upgrade that causes the engine to run less than optimum due to what was mentioned above. Additionally, because of the implementation of OBD systems, car manufacturers use more standardized designs for these new vehicles. It is too costly to make mid-year changes that redesign for example---an exhaust system.
However, on our classic cars, trucks, and street rods this is not the case. A vehicle manufacturer may keep with the same design during an entire model year (or longer), or may have numerous changes throughout a production cycle. What if a vehicle manufacturer prior to the 1990's used "X" sourced exhaust manifolds for assemblies between August through October, but that supplier could not keep up with production (or had a problem), forcing the vehicle manufacturer to change. Then, a "Y" sourced manifold was used for the rest of the model year? And, what if these two manifolds changed the collector exit location? If a header manufacturer such as Sanderson wanted to build direct-fit headers for this classic vehicle we would need to create two variations of a header set (just for that ONE vehicle) if it were to be a direct-fit item! Imagine for a moment the number of vehicles built since the 1920's, and how many likely variations there could be. For example, some Ford applications have been know to have three or more variations of components in a single year. This is costly and a huge waste of time and important resources for any header manufacturer.
Headers manufactured for classic cars or street rods are built for more of a universal fit. We are not bound by the restrictions of OBD, and design our headers to offer the best fit for a variety of vehicle applications. Instead of building a specific header for each and every possible configuration, we at Sanderson will often redesign a popular header slightly to provide proper fit on an even wider range of vehicle applications.
What this means is that you WILL need to change the down pipes on your classic car, truck, or street rod to connect to your under chassis exhaust piping to your new headers. This is one of many primary activities at most muffler shops, and should not scare you away from adding headers to your classic Mustang, Thunderbird, Camaro, Buick Skylark, Dodge Dart, or any of the other numerous vehicle applications our headers are designed to fit.
In a way, we (as consumers and vehicle enthusiasts) have become accustomed to direct-fit terminology because it is the current standard for newer model vehicles. The osmosis of hearing or seeing "direct fit" or "smog legal" or "cat-back" in regular advertisements is understandable in how it can cause confusion with the requirements of our classic vehicles. Just remember, it is not the case. Headers for classic cars will require some changes to your under chassis exhaust piping during installation.