What is exhaust system balancing, and why do I need it? Infusing your ride with extra power, fuel economy, and sound is as simple as bolting on a performance exhaust system.
You may be wondering why so many aftermarket performance exhaust system manufacturers are offering dual exhaust systems connected by “H-pipe” or “X-pipe” sections. Not surprisingly, new technologies and refinements to exhausts have made something as simple as tubing as obsolete as the floppy disk. By managing exhaust CFMs, scavenging effects and velocity, exhaust pipes squeeze every bit of flow from modern systems. An X-Pipe or H-Pipe are two exhaust crossover pipe components that serve the same purpose, while operating on quite different principles.
An X-Pipe or an exhaust H-Pipe are at the heart of a performance exhaust system and bolted in the center of the car. Also known as a crossover pipe, each system works by balancing the exhaust pulses from either side—or cylinder bank of a V-style engine. The result is a smooth exhaust system flow and a more efficient engine. But what is the difference between the two?
Why an X-Pipe?
An exhaust X-Pipe muffler is, you guessed it, shaped like an x, and allows the exhaust to flow down the path of least resistance. At lower revs, turbulence is formed as exhaust gases try to shuffle past a second column of gases coming from the other side. While always producing more power than the restrictive factory system, the potential gains are not seen until higher rpms are reached. This is where an X-Pipe exhaust stands apart from the rest. Exhaust gas is pushed out harder as the engine spins faster. The X-Pipe merges this chaos into two uniform streams, allowing a smooth flow from engine headers to exhaust tips through the addition of this exhaust crossover pipe. Both streams keep each other up to speed, which draws even more spent exhaust out the cylinders.
Why an H-Pipe?
An H-Pipe exhaust is also shaped like its namesake and relies on exhaust system expansion to balance the cylinder banks. A small section of tubing in between the main pipes provides an area for gases to expand into during exhaust pulses. Only a small amount of exhaust flows from one stream to the other as both sides push back and forth in the center section.
While both X and H pipes serve the same purpose, they use different methods to build power and economy, all while providing a distinctive sound. Think of an X-Pipe muffler as being at home in a high-winding modern V6 or V8 while an H-Pipe conjures memories of tire-shredding torque in classic American iron.
Do not let the glorious Chevrolet Bow Tie horsepower fool you. Firing eight cylinders every 90 degrees in a 1-8-4-3-6-5-7-2 sequence is an inherently chaotic endeavor. Since the mass of the counterweights and flywheel mask this violence by smoothing out the power delivery of the crankshaft, it is easy to forget that eight individual combustion events are going down every 720 degrees of crank rotation. Alternating the firing order between the left and right bank of cylinders means that there is often a substantial difference in exhaust pressure between each bank. The result—at any given moment—is a traffic jam of exhaust molecules in one bank of cylinders when minimal backpressure exists in the opposite bank. While this recurring scenario reduces engine efficiency and horsepower, the solution is as easy as integrating a balance pipe into the exhaust system.
Adding a balance pipe is like downloading Google Maps for your exhaust. As combustion gases travel out of the header collector and into the intermediate pipe, if their progress slows down due to backpressure, a balance pipe redirects them to a less congested flow path. Just like the name suggests, they help to balance the flow between all the cylinders. Beyond that, they can even help with scavenging by having cylinders from the opposite bank of the engine create a negative wave to increase the overall flow of the exhaust.
In terms of both performance and price, balance pipes are so effective that GM has been installing them for decades on Corvettes and more recently on fifth-gen Camaros. Best of all, balance pipes can be added to any existing dual exhaust system. Before busting out the Sawzall and welder, however, there are many important factors to consider, such as the performance difference between X- and H-pipes, where to place them in the exhaust tract, cost, and potential horsepower and torque gains. Granted that balance pipes are rather simple devices, but there is far more to the science behind how they work than their appearance suggests.
Equalizing Flow
Balancing the exhaust system pressure from bank to bank is just one of the many ways an X- or H-pipe improves overall exhaust flow. With a conservative factory camshaft, the exhaust seemingly flows out the tailpipe in one continuous stream. However, exhaust waves travel in pulses, which become much more noticeable as camshaft duration increases. Consequently, reducing the detrimental effects of these pulses can positively impact horsepower and torque. It functions by taking the left and right banks of an engine’s exhaust and providing a crossover point to equalize flow from side to side thereby the balance pipes smooth out uneven exhaust pulses. Any given engine generates low- and high-pressure exhaust pulses because of the firing order. As these low and high pulses move downstream through the exhaust piping, they travel at different speeds. Having an exhaust system crossover helps draw these pulses out into a more balanced pattern, which ultimately improves engine output. Another benefit is that crossovers also decrease in-cabin exhaust drone.
Best Spot to Mount X-Pipe / H-Pipe Section
Many ask if the best spot to mount an X-pipe or H-pipe section is up front just behind headers (or exhaust manifold), toward the rear in front of mufflers, somewhere in the middle, or anywhere there’s room. Exhaust system experts say the best spot to put your section is generally toward the front of the exhaust system near the transmission.
X-pipes vs. H-pipes
Although X-pipes and H-pipes perform extremely well for a minimal investment in time and money, both offer unique properties that make one more suitable than the other depending on the application. The two biggest differences between an X- and an H-pipe are sound and power. Generally, the X-pipe will deliver a more high-pitched exhaust note, making a car sound more exotic, whereas an H-pipe gives a deeper tone with more of a traditional hot rod sound; though the difference in power gain between the two is very minimal. The X-pipe will usually make anywhere from two to four more horsepower than an H-pipe. The slight horsepower difference comes from the way the X-pipe creates a venturi effect, which helps pull the exhaust gases out of the cylinder faster. Overall, the main difference is sound rather than performance, meaning there are no pros or cons. It’s simply a matter of personal preference.
In addition to differences in sound and horsepower, both X- and H-pipes affect different parts of the powerband as well. An H-pipe tends to make more of a difference at lower rpm, while-X pipes will increase power more at higher rpm. As you can imagine, just by looking at each configuration, in the H-pipe the exhaust must make a sharp 90-degree turn, while the X-pipe offers a smoother transition. The X-pipe creates much more of a scavenging effect. That said, it is important to prevent the X-pipe from necking down too small or flow can be hampered. Both an X- and an H-pipe will smooth out the separated sound of the cylinders, while an X-pipe tends to blend all eight cylinders together more.
For all-out power, X-pipes seem to be the winner, but H-pipes boast several advantages as well. H-pipes typically offer increased backpressure compared to an X-pipe, which nets an increase in low-end torque. They are also more tunable because they offer more options in terms of the length of the crossover, the diameter of the tube, and the size and location of the transfer hole. As a simpler design that takes up less space, H-pipes have more options as to where on the exhaust system the crossover section can be placed. While performance is a large consideration when designing an exhaust system, vehicle packaging is also a huge factor. Depending on the application, an X- or an H-pipe might suit the chassis better, but an H-pipe certainly offers more options as to where it can be placed.
Which Pipe is Best for You?
It can be exhausting choosing the right exhaust system for your ride. If you have got a newer car, and you want to be sporting that feisty zing every time you hit the gas, the X-pipe exhaust option will help to sharpen your tone and your power output along with it.
If you have a more classic muscle car that needs that throaty roar, an H-pipe gives you that borderline obnoxious sound while still providing you with the most performance gains possible.
