Let's Get Technical
"Even if running a radical cam and a supercharger, it is best to select a reasonable, smaller primary tube header set, unless then engine will spend most of its time at full throttle."
It is no secret that a good set of headers is one of the best performance investments. In fact, most engine builders say headers are among the first things we should upgrade when modifying our engines. But before we plunk down our hard-earned cash, we must remember a couple of factors that will determine what works best for our particular application.
The first thing to consider is the vehicle's intended use. Are we building a daily driver, a sometimes bracket racer, or a dedicated quarter-miler? The RPM range where we want the most torque, along with the engine's displacement (size), plus any other serious modifications and power-adders (camshaft, blower/supercharger, cylinder heads, nitrous, etc.), are equally important factors.
Stock manifolds are mass-produced and designed to clear all accessories offered for the vehicle in which the engine was originally installed. So naturally, factory exhaust system performance is compromised by manufacturing requirements. Tubular headers are built for improved flow, torque, and power — and their design can be highly specific.
Let's look at how headers work and clear up a couple of common misconceptions. First is the size of the primary tube. It is easy to assume the bigger the primary tube, the better, but that's not the case.
The fact is, primary tubes that are too large actually cost torque and horsepower by slowing down the rate at which the exhaust gases travel through the system. Think of our engines as an air pump. Every time the exhaust leaves the combustion chamber, it is being forced into the primary tube for that cylinder.
Smaller-diameter primary tubes carry less volume than larger ones, but the exhaust in the smaller tubing flows faster. Until the engine reaches the RPM at which the sheer volume of exhaust gases requires larger primary tube diameters, smaller tubes will scavenge the cylinders more efficiently. If operating the engine in the 1500 to 3500 RPM range, which is typical for a street-driven vehicle, we definitely want 1-1/2" to 1-5/8" primary tubes for any small-block engine and 1-3/4" to 1-7/8" for a big-block engine. Any bigger and we will lose a considerable amount of low-end torque. Beyond 3,500 RPM, it is a question of where we want the power peaks. We can see from the dyno chart above that small-tube headers do not lose their edge in horsepower and torque until the engine exceeds 5500 RPM.
Even if we're running a radical camshaft and supercharger, we are often better off sizing our headers smaller rather than larger, unless we plan to spend most of our driving at full throttle. We size our headers correctly for even the most heavily modified street motors.
The second biggest controversy in header design is the "long-tube" versus "equal-length" vs "shorty" styles. Which is best? Like most performance products, there are advantages and disadvantages to both.
Full-length exhaust headers with equal-length primary tubes have been shown to produce slightly more power on an open exhaust system, but not as consistently on a street system with mufflers. Equal-length short headers are offered by some manufacturers for late-model emission-controlled vehicle applications. The fact is, most street motors with shorty headers will produce the same power as they would with expensive equal-length headers at RPMs where a typical street engine spends most of its time.
Equal-length tubes can produce more power, true. However, they must be the right length for the specific motor at the RPM range where you want the power. That means lots of custom fabrication and dyno testing, which translates into lots of time and money.**
**NOTE: Powerful software is available for accurately calculating the header primary tube size and length for a specific engine. This is great for racing applications and for those looking to extract every last 1/4 horsepower from an engine within a specific RPM range. These programs require knowledge of and inputing a substantial amount of information. If this is of interest to you, reach out to one of our resellers, Century Performance Center, that offers this as a service.
For racing applications, the slight gain may justify the cost, but competition cars are more easily built "around the engine" than street cars. For street applications, and when we are working within the confines of a given body style and chassis, with motor mounts, starter, steering linkage, and accessories to think about, the way the headers fit becomes more important.
This is where the "shorty" style header shines. We get a significant performance increase over stock exhaust manifolds at an off-the-shelf price. Plus, Sanderson Headers provide excellent clearance around spark plugs, the starter, and chassis components, as well as ground clearance for lowered vehicles. The chart below illustrates one example of the small sacrifice in power we trade off for the much lower cost and easier installation of compact headers. However, we are not sacrificing at the RPM levels where a street application spends most of its time, idle to ~3500 RPM.
We build hundreds of custom-fabricated headers for one-of-a-kind cars, but for most vehicles, you can get the performance you need with a set of Sanderson Headers from our extensive product line.
Our headers are designed to fit right and produce the power you expect. Plus, the use of top-quality materials, construction, and patented flange design gives you lasting value down the road. Hook 'em up to a well-engineered exhaust system, and you'll feel the difference!
Source of Chart Data:
Our Thanks to Chevy Action! Magazine
Test Engine:
- 433 cu. in. big block Chevy
- 10.4:1 compression
- Holley 780cfm carburetor
- Oval-port heads with 2.09" intake valves and 1.88" exhaust valves
- High-performance mechanical camshaft, specs 250°/259° duration at 0.050 lift
Sanderson Headers
517 Railroad Ave
South San Francisco, California 94080
ph. (650) 583-6617
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