Basics of Racing Headers

The majority of stock exhaust systems do not have the capability of transferring enough exhaust gas when the engine is at high speeds. Some of the things that restrict the flow include catalytic converters, exhaust manifolds, mufflers, and other connecting pipes sending residue from combustion away from the engine.

An increase in power levels brings about a proportionate increase in the amounts of exhaust. Thus, the system demands more. For this reason, header manufacturers now make bigger pipes available for rpm power gains.

Since by-products of combustion do not burn twice, exhausts systems that are unable to get rid of exhaust gas can contaminate fresh air/fuel charges. Exhaust-flow velocity remains an important aspect of an efficient exhaust system. When the rpm is low, the flow rate will be slow. The flow rate will increase when the engine speed does.

Furthermore, increasing the restrictions will slow down the velocity and power once again. Interestingly, ignition spark timing, compression ratio, camshaft design, and piston displacement also affects the velocity and power. Sizing of system components, like headers, can be keyed to piston displacement and engine speed.

What Do Primary Pipes Do?

The primary function of a primary pipe is to set the original rpm point, where a torque boost is generated by the headers. Bear in mind that intake and exhaust systems can be adjusted to different engine speeds. Hence, it is possible to narrow or broaden an overall torque curve by the dimensioning intake and exhaust systems separately.

Several variables are responsible for how engine performances are affected by headers. These include the length and diameter of the primary pipe and collector. For headers, the flow rate is determined by the primary pipe diameter. At peak torque, the mean flow velocity is 240-260 feet per second (fps). However, this is usually determined by the mathematical basis used for the calculation.

When the length of the primary pipes are adjusted, the amount of torque produced below and above the peak-torque rpm is affected. Increasing the length of the primary-pipe gives the reverse effect of reducing the length. The diameter of the primary pipe plays a huge role in determining the torque curve.

What Do Header Collectors Do?

Collectors also affect the torque below peak torque. Adding more collector volume typically alters the torque. At below peak torque, collector helps to improve the engine. Joining collectors also boost low-rpm torque as a result of an increase in overall volume of the collector.

Header Size

When the piston moves downward, cylinder pressure will be less than atmospheric pressure. The intake flow velocity will then depend on engine speed, piston displacement, and the inlet path’s cross-section area. The exhaust flow velocity depends on engine speed, piston displacement, the exhaust path’s cross-sectional area, as well as the cylinder pressure during the exhaust cycle.

Matching Headers to Objectives

By knowing any tow of the three variables mentioned earlier (rpm, piston displacement, or primary pipe diameter), you can simply determine the third variable.

• Peak torque rpm = Primary pipe area x 88,200 / displacement of one cylinder.
• Primary pipe area = Peak-Torque rpm / 88,200 x displacement of one cylinder.
• Displacement of one cylinder = Primary pipe area x 88,200 / peak-torque rpm.

Always remember, headers are just a single aspect of the entire power equation. When you are looking for a way to improve power and performance in stock racing or drag racing situations, headers should only be considered as one aspect of the entire compression, camshaft, cylinder head, and induction system.

The area of the header pipe obtained here may not be as accurate as some advanced computer-modeling software. However, it can still serve as a valuable quick-and-dirty to determine your choice of the header.

Conclusion

A lot still remain about the science of exhaust system which cannot be explained in this article. It is still important for you to note that the final combination of parts should put all the components into consideration as a single unit, instead of looking at headers as a single entity. By treating as a complete system, you will be able to determine the best overall power of the engine.