By Jim Kerr

The young automotive students at the college where I teach often ask me how they should “hop up” their cars. They are looking for more power, quicker acceleration, and better fuel economy, too. Many of these young students drive compact import cars referred to as “tuners.” With splashy paint schemes, custom wheels, aftermarket exhaust systems and powerful audio systems, these cars have already seen lots of modifications, but they still ask about economical (cheap) ways of making power. Often, their questions are about the benefits of cold air intakes.

Factory air intake systems are a compromise. They are designed to keep intake air noise levels low, heat intake air during cold weather and separate rain and snow from the intake airstream. They work well, but are a compromise for performance. The simplest modification is to add a high flow air filter. K & N air filters have to be the best-known brand of performance air filter on the market and increase airflow while still providing effective filtering if they are maintained properly. If you want really good filtering, take a lesson from the Baja 1000 desert racers – they use really large filters, some 2 or 3 feet across. The large area can hold a lot of dust without restricting airflow. Fitting a filter this big into a street driven car can be difficult however, if not impossible.

Other modifications may include ducting cold air into the intake system. Approximately every five degrees Celsius drop in intake air temperature will increase power about one per cent. Under hood temperatures may be in the 70 to 80-degree C range in tight engine compartments so even on a hot 35-degree day using outside air will provide substantial performance gains. There can be many ways of ducting cold air into the intake manifold. Scoops can be installed below the bumper and flexible ducting run up to the air cleaner. This makes for an unobtrusive setup but it also has problems. There is more dirt and dust down low, so air filters may need changing more often. In my part of the country, insects in the summer or snow in the winter can block airflow through the system.

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