A good exhaust system can give your car more power and make it sound better, but what constitutes "good," exactly? It's largely down to the shape of the pipes, providing exhaust gases with the path of least resistance, so an engine doesn't have to work as hard to exhale them. Additionally, it creates some room for sound to resonate and create that sweet mechanical music.To prove that, Justin from The Fabrication Series YouTube channel built seven exhaust systems and tested each one on a dyno to find out which bend is the best. He tested everything from the industry-standard mandrel bend to the crinkle bends usually found on exhaust pipes from auto parts stores, to a wacky noodle exhaust made entirely of curved pieces. For each system, he measured horsepower and back pressure, but also used a thermal imaging camera to track hot spots.The mandrel bend is the standard because it provides a consistent diameter between straight and bent sections of pipe. It was used as the control for this experiment, providing a baseline output of 144.8 horsepower (averaged across three dyno pulls) in the Mitsubishi Lancer Ralliart test car. Back pressure averaged 1.42 psi, while noise averaged 101.4 decibels.The Fabrication Series via YouTubeFirst up for comparison was the crinkle bend, which was not favored going in. This type of bend decreases the diameter of the tubing and creates ridges that cause turbulence. Yet while average back pressure was higher at 1.71 psi, it produced about the same amount of power and was 1.0 decibel quieter, likely because the bent portions were made from aluminized steel that's more sound-absorbent than the stainless steel used in the mandrel bend system.AdvertisementAdvertisementCrush bends made with a tubing bender also have a smaller diameter, but the fabrication team tried to get around this by using tubing the next size up for the bends, the theory being that once it was crushed down, it would have the same diameter as the straight sections of tubing it was connected to. Two versions—2.0-inch and 2.2-inch—were tried, and both produced about 1 hp more than the control system. The smaller bend had a lot more back pressure, though, while the larger bend sounded a bit nicer.Okay, what about no bends at all? Miter joints and pie cuts both averaged 146.3 hp—the highest in the test. Back pressure for both was higher than most of the bend options, but noise was within a few tenths of a decibel of the other systems. The difference between bends and joints was less important than just avoiding both in the first place.The all-bend, drunken exhaust pipe had about twice the back pressure of the mandrel-bent system, at 2.83 psi. Thermal imaging also showed that exhaust gases were moving so slowly through it that there were significant temperature differences from one end to the other. It's also about two feet longer than the other systems. But it only lost 0.4 hp to the mandrel-bent system, so there's that.Of course, if you just want more power and want to avoid a lot of costly fabrication, straight pipes are the way to go. Cutting the exhaust off after the catalytic converter yielded the most power—149 hp—but also the most noise, at 110.77 decibels. If you're going to do this, you'd better hope there are no noise ordinances where you live.AdvertisementAdvertisementThe differences in horsepower and sound might be small, but that's because the Lancer Ralliart doesn't make a lot of power or noise to start with. They'd be more noticeable with a louder, more powerful engine. The back pressure numbers tell the real story. The most unconventional shapes showed why they're unconventional, with higher numbers that restrict airflow and dampen performance.
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