Buying a new exhaust system can be one of the most exciting, and most cost-effective upgrades any auto enthusiast can make to their vehicle. But beyond remotely-controllable mufflers, masterfully crafted headers and flashy endtips, there are two far-less conspicuous exhaust components that need to be considered: bent tube sections and donuts.
Ask any exhaust system designer and they’ll tell you: the key to getting the best performance from an exhaust system isn’t in resorting to larger diameter tubes: it’s in maximising airflow. Every section of tubing, and every joint between those sections has to be optimised in order for exhaust gases to move as quickly and smoothly as possible. That’s why our tips for ensuring the best possible gas flow are centred on donuts and mandrel bent tubing.
High Performance Tubing and Donuts Make the Smooth Diameter Difference
It’s a fact: when it comes to high performance exhaust tuning, the importance of using only mandrel bent tubing and premium exhaust donut solutions is arguably the most overlooked aspect of exhaust design. Together, these two components are the keys to eliminating flow-disturbing kinks and deformations that occur where tube sections meet, and where the altered inside diameters of curved tube sections can create performance-starving backpressure.
The smoother the inside diameter, the more effective an engine is at producing power, making donuts and mandrel bent essential for optimised output. By keeping exhaust backpressure low and exhaust scavenging high, the smooth-diameter characteristics provided by mandrel bent tubing and donuts are directly responsible for achieving the following:
- Producing instant power gains. A smooth, uniform inside diameter throughout the full length of an exhaust system is crucial for maximising exhaust velocity, and boosting engine output. And as hot spent gases flow naturally from high to low pressure, consistently-sized mandrel bent tubes and donuts ensure the flow remains steady at the most likely points of resistance.
- Increasing engine efficiency. An engine that doesn’t need to work hard to produce power has an automatic efficiency advantage. And regardless of their diameter, the reduction in backpressure that’s possible with uniform-dimension mandrel bent tubes and donuts allow engines to deliver heaps of extra power while still staying within their performance window.
- Improving system reliability. Consistently-sized internal diameter tubes don’t just increase power and efficiency: they also improve system reliability. With their smooth internal diameter surfaces, exhaust systems equipped with mandrel bent tubes and high performance donuts are less likely to experience fatigue-related stress or breakage due to turbulence or resonance.
Make no mistake: any exhaust mod or component that increases airflow, can ultimately be counted on to increase exhaust velocity and engine performance. It’s finely-tuned exhaust mods that produce the most consistent advantages, though. That’s precisely what owners expect from mandrel bent tubes and high precision exhaust donut combinations.
Mandrel Bent Tubing Prioritises Superior Exhaust Scavenging
When it comes to curved sections of exhaust tubing, mandrel bending isn’t just the tuner’s preference: it’s the benchmark for high performance exhaust design. Instead of crush bending exhaust tubes to fit around chassis and suspension components, tubes bent on a special mandrel bending machine are the key to maintaining smooth, consistent tube diameters inside every bend.
Although mandrel bending is considerably more labour-intensive more than standard compression bending, the result is a tighter, smoother-diameter bend that’s free from internal restrictions and backpressure, delivering a core of instant benefits that include:
- Better spent gas flow. The turbulence and internal restrictions created by crush bending can actually reduce exhaust flow by as much as 10%. Mandrel bending, however, is critical for the uninterrupted, smooth diameter scavenging that’s needed for spent exhaust gases to flow freely at all times.
- Greater exhaust durability. Durability is a benchmark of any high quality exhaust system. Unlike crush bent tubes though, mandrel bending doesn’t create excess tubing stresses that could result in motion- or heat-related fatigue or cracks.
- Improved exhaust note. Exhaust designers know that sound and performance invariably go hand-in-hand. The improved airflow produced by smooth diameter tubes is capable of producing an exhaust note that’s both deeper and richer than would ordinarily be possible with crush bent tubing.
Conservatively, the difference in engine torque and output between using crush bent or mandrel bent tubing can be as much as 5% in any configuration. That makes mandrel bent tube sections a priority for complex custom exhaust systems where unusual engine and suspension setups require creative plumbing solutions.
And as mandrel bent tube sections are readily available through the aftermarket in a wide range of radii and diameters, tuners are able to order the precise number and dimension of tube segments they need without the time and cost of having to make their own custom bends.
Leakproof Donuts Keep Exhausts Pressurised and Efficient
Let’s be honest: while exhaust donuts rarely ever warrant a second notice, the job they perform in ensuring proper pressure equalisation throughout the system is irreplaceable, especially in high performance setups. These are environments where even under the best operating conditions, high rates of thermal expansion and severe vibration can ruin a system’s ability to scavenge properly, effectively canceling any advantage that might be achieved with a high performance system. A smooth-diameter leakproof seal is essential for superior exhaust scavenging, and flexible, vibration-resistant donuts guarantee the best operating conditions possible.
With their combined graphite and metal composite construction, exhaust donuts are capable of out-performing even the highest performance copper gaskets in virtually every aspect, especially when it comes to:
- Maximising engine efficiency. Regardless of how much power an engine produces, smooth diameter donut exhaust gaskets are crucial for ensuring the exhaust system remains pressurised, and is delivering maximum exhaust volume flow and efficiency at all times.
- Reducing unwanted exhaust noise. Unlike flat-surfaced copper and carbon fibre gaskets, high performance exhaust donuts do an impeccable job of filling the gaps between exhaust flanges, thereby reducing unwanted exhaust noise while still assuring maximum scavenging.
- Increasing heat-boosted airflow. Heat may be the most destructive by-product of any engine, but it reduces the density of spent exhaust gases, allowing for better scavenging. High performance exhaust donuts are designed to withstand continuous temperatures to 600°C, providing a solid, yet flexible seal between exhaust flanges that’s an immediate aid to airflow.
With their ability to form smooth, leakproof seals between any two mating flanges, donuts are invaluable when it comes to improving airflow and boosting output, particularly on turbocharged engines. And by maintaining consistent airflow and draw-through scavenging, they can even play a role in improving fuel economy throughout the life of the engine, regardless of whether it’s equipped with an OE replacement, or high performance exhaust system.
The Final Word
At the end of the day, it’s important to remember that every part of an exhaust system is critical. And while canyon-sized headers and bass-noted tailpipes are genuine attention-getters, it’s the small parts that deliver the leak-proof/turbulence-free performance needed for maximum exhaust gas flow throughout the entire system.
Mandrel bent tubing and high quality exhaust donuts assure the optimised, smooth diameter airflow that every engine needs to perform its best. They’re the discreet components that exhaust tuners turn to for big performance results.
