If you need more power from the engine, then changes to the internals will provide bags of added performance and a faster car. But swapping out pistons, and connecting rods and crankshafts are often the last additions to a revised engine. Other mods set the grounds for these to work as they should. More power means pushing more air into the engine, with an aftermarket air intake doing the honours. And more air (and matching fuel ratios with beefed-up injectors) coming in for combustion means more spent gases leaving through the exhaust. These are just one way to add a few more horses, and with the louder and raspier sound, one way to stand out from the crowd. 

Why Consider an Exhaust Upgrade?

Stock exhausts are one area where carmakers do a lot of cost-cutting in order to allow for more affordable cars. Crush-bent mild steel isn’t exactly the best material for high exhaust temperatures and pressure and is prone to kinking and deforming, as well as corrosion if not treated with a coating. The narrower tubing additionally runs the risk of increased back pressure or exhaust lingering in the piping and making its way back toward the exhaust valves. This robs the engine of the space for a new gulp of air needed for the next combustion cycle, so also negatively impacts efficiency and performance. In enduring cases, backpressure can also damage valves, camshafts, and pistons among other parts. 

Aftermarket exhausts come in different configurations, and this will depend on the type of engine and specifics such as forced induction. What’s common in all types though, including cat-back exhausts, is the use of higher-grade materials (stainless steel as a starting point, and titanium or carbon in high-end variants), wider tubing, and solutions to free up the airflow. There’s also the option of tuning the sound that comes out of the exhaust tips. The result is that not only does the engine have room to breathe, but there is a considerable increase in horsepower and torque across a wider power band. 

Configuring Your Exhaust With Different Parts

Exhaust systems are often of the modular type, meaning you can change parts at will. This includes headers and exhaust manifolds, downpipes, catalytic converters, mufflers, and the use of crossover pipes. Each part helps with exhaust flow. Headers and manifolds are the first parts that deal with the exhaust leaving the cylinders and exhaust valves. Revised and aftermarket versions perform better in exhaust scavenging, or sucking out exhaust during the combustion process. The revised designs are mandrel bent to cut down exhaust restrictions and the buildup of backpressure by increasing exhaust velocity and pulling spent gases out faster. Common designs are 4-in-1 header and Y-configurations merging in a wider collector pipe. 

Downpipes link the headers to the rest of the exhaust tubing. Between the two parts in stock exhausts is the catalytic converter. In racing and track application, buyers go with cat-less exhausts without the use of a converter, but with wider and straighter tubing instead. Catalytic converters (or ‘cats’ for short) are exhaust parts introduced in the late 1970s as a way to reduce emissions. They are now mandatory in any car for street use and collect toxic gases from combustion. From here, tubing extends into mid-pipes at the ends of which you’ll find a resonator to prevent exhaust droning and a muffler to quieten the noise. 

Mufflers consist of a series of baffles, chambers, and perforated tubes, in addition to sound-deadening materials, and come in different combinations that let you fine-tune the exhaust note. Where there are two pipes exiting the headers, exhausts can take on some interesting designs, such as X-pipes and Y-pipes and these can be resonated or non-resonated. Lastly, let’s not forget where you have the most freedom in terms of designs, materials, and looks, Tailpipes are what you see at the end of the tubing, and come in polished steel, chrome, carbon, or titanium. These terminate in the exhaust tips. 

Axle-Back, Cat-Back, and Header-Back Exhaust Systems

Axle-back exhausts replace all the components in the stock exhaust from the rear axle to the exhaust tip. This includes mufflers, tailpipe extension tubes, and the tailpipes themselves. While they offer some performance improvements, being in wider diameter and better made, axle-back systems are mostly about tuning the exhaust sound. 

There’s more to be had with cat-back exhausts. These replace all factory parts from the catalytic converter down to the tips, including the factory mid-pipes, resonators, mufflers, tailpipe extension tubes, tailpipes and exhaust tips. The tubing is wider, often 3 inches in decent performance upgrades to 4 inches or more in exhausts lining high-end performance street vehicles, and serves to limit backpressure and increase scavenging and exhaust flow. Moreover, these systems offer some unique muffler configurations, namely with electronically valved systems controlled from the cabin or with a remote to change between different sound profiles. Lastly, there’s more variation in tailpipe extension pipes and exhaust tips with different designs and materials. The result is you get a substantial boost in power over factory figures, more low-end torque (meaning the car pulls better from earlier on), improved sound, better looks, and less stress on the internals. 

If you want to go all out, and completely remove the whole stock exhaust, then header and turbo-back systems are what to look for. Aspirated engines use headers in revised designs, while engines with turbos will have additional piping and larger downpipes to ease airflow. Conservative numbers are that you get between 5 to 10 per cent of added power. For instance, in cars like the Subaru STi this means close to 30 added horsepower. Other changes are similar to cat-back and axle-back exhausts. 

Finding What You Need

Budget will be the first thing to think about when buying an exhaust. As stated, this is just the first of many modifications when you’re serious about increasing power and performance and expenses can soon get out of hand. Generally, there are three tiers of brands – those selling exhausts as general factory upgrades and available for most cars, mid-tier systems that combine improved materials and production process with better designs, and high-end exhausts geared toward track and performance cars and costing in excess of five figures. Pricing is also more in line with the vehicle. All will give you much more than what you currently have. 

Next, ensure is getting an exhaust that is compatible with your car. You can go for any of the three types of exhausts but pay attention to the types of fuel, the number of cylinders, and whether the engine is aspirated or with forced induction. Brands and retailers make these easy, with distinct product lines and exhaust systems built specifically for your make and model. And lastly, get the exhaust installed by a pro if you’re after the best results.