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17th Annual Technical Forum: Performance Exhaust

Counterman magazine presents 15 technical and sales topics in an easy-to-read question-and-answer format for the magazine’s annual Technical Forum. This article appeared in the August 2009 issue.

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Q. My truck doesn’t get very good gas mileage. If I replace the stock muffler with a performance muffler, will it help?
A. It should. Uncorking the exhaust system with a low-restriction, free-flowing muffler is a great way to improve fuel economy and power at the same time. Diesel trucks, in particular, often benefit most from replacing a stock, restrictive muffler with an aftermarket performance muffler.

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Most manufacturers claim power gains of 15 to 25 horsepower or more with their products, and maybe 5 to 10 percent better fuel economy. The larger the displacement of the engine, the more it usually benefits from upgrading to a free-flowing exhaust system. This is especially true with big turbocharged diesel engines. Reducing exhaust backpressure allows boost to come up more quickly and to reach a higher level. Throttle response is also improved, and the engine usually runs cooler.

Options include a direct fit replacement muffler designed to fit your vehicle, or a universal muffler that’s about the same length as the original. Either will work, though a muffler that has been designed specifically for your truck will probably deliver better sound and performance than a one-size-fits-all muffler.

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Installing a big bore muffler on a small car with a four-cylinder engine, for example, can often produce a very unpleasant exhaust tone because the muffler isn’t tuned to take out the higher frequency exhaust pulses. The result is a loud, buzzy, annoying exhaust sound.

In the case of your truck, you want a deep, powerful sound. A complete cat-back exhaust system would provide the biggest gains. Complete systems typically use smooth mandrel bent tubing that may be a larger diameter than the original. The system is a simple bolt-on installation that replaces your old stock system.

Higher-quality aftermarket performance exhaust systems are typically made of stainless steel for extended durability and corrosion resistance. Most premium mufflers and systems are plasma or TIG welded to maintain the strength and corrosion resistance of the stainless steel.

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The pipes and muffler shells are usually made of aircraft-quality T-304 stainless, but there are less expensive and less durable grades of stainless available, or plain steel or coated steel if you’re looking for a budget-priced system or muffler. It all depends on how much you want to spend, and how long you want your exhaust system and muffler to last. Stainless steel pipes and mufflers will usually last 10 to 12 years or more with everyday driving, while plain or coated steel typically goes about 3 to 5 years before it succumbs to rust.

A stainless performance muffler can retail for $200 to $300 or more, and a complete system can easily cost $500 to $800 or more depending on the make and model of the vehicle. Polished stainless steel mufflers and exhaust tips are also available if you want to dress up the appearance of your truck.

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Q. Can I replace my catalytic converter with a straight pipe to improve performance and fuel economy?
A. No. All street-driven vehicles that were originally equipped with a catalytic converter must retain a converter. A vehicle without a converter will not pass an emissions test. Removing the converter causes a significant increase in exhaust pollutants, and does not improve performance that much anyway. Aftermarket replacement converters that have a more free-flowing design are available, and are a good upgrade alternative if you are looking to maximize the performance and fuel economy potential of your vehicle.

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