It’s an accepted part of hot rodding lore that headers help make more power and torque on any engine versus the typical stock cast manifold, but do you know why? It’s all about flow, right? Well, yes and no. It’s more about optimizing how the exhaust exits the engine’s combustion chamber, but there is much more to it than just using the largest pipe possible. Before you throw down some hard-earned hundies for a set of tubes for your car, it pays to have a basic understanding of what you’re getting in return and why.
Why Are Headers Better?
Aside from the restriction created by their very short runners and log, OE exhaust manifol
If an internal combustion engine is just an explosion-powered air pump, then how the air exits the engine is just as important as how it gets ingested. As the piston travels through the exhaust stroke, the burned gases are expelled past the open exhaust valve and into the exhaust manifold. By nature, manifolds have very short runners that dump into a common plenum (or "log"), which causes the gases from each cylinder to build up pressure in the manifold. That backpressure can not only prevent all of the exhaust from being emptied from the chamber, the proximity of the log to the chambers can allow exhaust from one cylinder to flow back into another cylinder during cam overlap. If all the exhaust gases are not removed from the cylinder, the intake charge will be diluted, meaning less power will be made. On top of that, backpressure also requires power to be expended to force the gases out of the cylinder, so there is a loss there as well.
Four Common Header Types
4-into-1 Long-Tube: This is the classic long-tube header that everyone is most familiar with, and comprises the vast majority of the aftermarket offerings for street and race application. The benefit of long-tube headers is the significant decrease in backpressure on the cylinder due to the separation of exhaust gases into their own individual pipes. Their length also prevents the crossflow of exhaust from one cylinder to another. These are also the most versatile headers since they can be tuned in different ways via primary diameter, length, secondary (collector) diameter, and shape to account for different horsepower and operating ranges. They’re the go-to design for most hot street and race cars.
Tri-Y headers, like these from Doug’s are traditionally designed for a midrange torque inc
Tri-Y Long-Tube: Tri-Y headers came to popularity when they were used by Shelby for the GT350 Mustangs. The tri-Y design combines a short primary that is paired with another cylinder that is synchronized in the firing order into a 2-into-1 collector that steps to a larger diameter secondary tube. The two secondary tubes are then merged into a final 2-into-1 collector creating an overall length similar to a 4-into-1 design. The traditional design works well to build more torque from idle to 4,500-5,000 rpm, so they are very effective for street use, however, autocrossers and road racers also love them for their midrange torque and increased throttle response as well. NASCAR teams use a derivative design, called a 4-into-2-into-1 (4:2:1), which uses much longer primary and secondary tubes for higher-rpm effectiveness.
Shorty & Block Hugger: Shorty headers primarily came into existence because of emissions systems that require catalytic converters and oxygen sensors located in a specific range close to the exhaust ports. Shorties are better than most manifolds since they offer short runners that do not combine into a single log, which helps separate exhaust gases and prevents crossflow into another cylinder. Nevertheless, the tubes are too short to maximize potential gains and they lack a collector of any significant length, which also hurts overall gains. Some performance-oriented cars actually come from the factory with a shorty-style header, Mustangs for example. These factory headers work pretty well considering the confines and are often only bested by shorty headers that have runners dyno tuned for increases on specific engine combinations—and by long-tubes, of course.
Mid-length headers, like these from Hooker, maintain stock ground clearance while still gi
Mid-Length: Brought out as an alternative to shorties without the ground clearance issues of full lengths, mid-length headers keep the tubes and collector up above the chassis but allow for longer primary lengths. Not much length is sacrificed in the primary tubes, but the collectors are very short, which does affect their tunability. Mid-length headers will almost always make more usable power on the street than shorties, although not quite as much as long-tubes or tri-Y designs.