All About GMC Sierra Headers

Exhaust scavenging is the effect of one exhaust pulse shooting out of the exhaust port into the header such that exhaust velocity is optimized and a  low pressure area follows suit. This low pressure area then helps suck the next exhaust charge out of the cylinder and accelerate it down the primary tube before reaching the collector. Proper scavenging lessens restriction and promotes complete evacuation of exhaust gas from the combustion chamber, which then lets more unburned air into the chamber upon the intake stroke. Having traces of the last exhaust charge remain in the combustion chamber during the next inlet and power cycle reduces performance because there is simply less oxygen available to make power.

A shorty header mitigates this problem by increasing the primary tube diameter and length. Doing so improves flow and scavenging effect which results in an improvement in horsepower and torque. Generally speaking, a shorty header will net 10-15 horsepower at the peak and up to 20 at various parts under the curve. Torque should follow suit with similar numbers, however some dyno testing shows certain models to have gained between 20-45 lb-ft of torque between 2500-3500 RPM, which is certainly an important RPM range for a Sierra pickup.

On top of these power and torque improvements, shorty headers are less expensive than their full length counterpart and are much easier to install. Their compact designs make them easier to fit in the engine bay and are engineered to work with the factory mid-pipe.

It is interesting to note that the aftermarket has very few short style exhaust headers available for the latest generation (2014-2018) Sierra pickup, where the previous 2007-2013 generation had considerably more to choose from. This, I believe, stems from a change in the factory design between the two generations. 2007-2013 Sierra pickups were equipped with a truly sorry-looking log style manifold whereas it seems for 2014 GMC seriously upped their game and has been manufacturing the newer Sierras with a better, almost shorty-like model. There may not be a major difference anymore between the stock manifolds and an aftermarket shorty header on newer Sierra trucks.

Full length headers, or long tube headers, take exhaust efficiency to the next level. These headers feature highly extended primary tubes (30” or longer) that culminate in a large collector. The advantage here is related directly to the length of the primary tube. A longer primary tube can better accelerate the exhaust pulse before it reaches the collector, thereby improving scavenging and significantly reducing the effort it takes for the engine to exhale. In addition, this scavenging ability is particularly exemplified at low RPM which greatly benefits low end torque production, an area that is crucial for a hardworking Sierra pickup. In fact, an appropriately sized long tube header should maximize power and torque gains under the curve as compared to a shorty header. This is an ideal situation for a pickup truck where torque and power are needed down low in order to pull heavy. Furthermore, whilst long tube headers are better known for low to mid-range torque production, they will also support more peak horsepower due to sheer volumetric capacity. A 4.8, 5.3, 6.0 or 6.2 V8 will move a lot of air at high RPM and a long tube header will provide ample evacuation capacity without fail.

Common primary tube diameters (measured from the outer diameter) are 1-3/4” and 1-7/8”. There is something to be said about selecting a header that is too large for your engine – it can slow down the exhaust and hamper performance. Fortunately, aftermarket testing has shown that the Gen IV and Gen V GM small-block motors love long tube headers and produce fantastic results with either size.

Having said all that, long tube headers do not arrive without some disadvantages. First off, there is the installation process. Equipping any production vehicle (not just a Sierra) with aftermarket long tube headers can be a chore. They need to be installed from underneath the truck and often times a lot of disassembly or relocation of other engine components needs to take place in order for them to fit and have adequate clearance.

Long tube headers will not work with the factory GM mid-pipe, either, thus you have to purchase a matching Y-pipe or X-pipe as well, driving up overall purchase cost. Depending on what mid-pipe you select, it may not be emissions legal in all states.

Regardless of which type of header you choose, they both share common construction and finish features. Basically, any aftermarket header will be made of mild steel or stainless steel and sport either a plain, chrome or ceramic coating.

As far as steel construction goes, stainless steel always has the advantage over mild steel. It is stronger, more durable and is much more resistant to corrosion. Of course, stainless steel is more expensive. A mild steel, unfinished (no protective coating) or chrome header will perform the same as a more expensive stainless steel version, but it certainly won’t last as long. And given the rougher environments that a Sierra is likely to be exposed to, a chrome or unpainted header cannot be recommended.

On the other hand, both mild steel and stainless steel headers can be had with a ceramic coating. This heat absorbing coating seals the metal underneath and should prevent it from rusting in addition to lowering the under hood temperature.