Boxster Intake Modifications

Porsche's designers have to design an intake system that is quiet (like the exhaust system, even the intake system can be noisy!), cleans the intake air, prevents water, dust and hot air from being sucked into the engine, works to keep emissions low, and still allows as much power as practical. But properly done, the intake system can be modified to safely allow more power from the engine.

High-Performance Air Filters

Air filters, and their associated housings and tubes, usually present a significant source of restriction to the flow of intake air. By reducing that restriction, power may be increased. It is also possible to design "ram-air" intakes that take advantage of complicated aerodynamic laws to force air into the intake at a higher rate than would otherwise be possible.

Low-Restriction Air Filters

If competition rules limit your allowed modifications, or you're worried about voiding your car's warranty or passing smog inspections, get a low-restriction replacement air filter element -- just don't expect much improvement.

I've replaced the standard air filter element with a K&N air filter element in the hopes of gaining a little more power. It is shaped just like the standard filter and fits nicely into the standard air filter housing without any modifications. This modification is legal in the Boxster's SCCA "Stock Category" autocross class (they even allow you to remove the element entirely though all housings, tubes, ducts etc. must remain in place). I haven't heard or felt any difference, but my tests seem to indicate that it may have helped performance by a few hundredths of a second. Probably not worth the effort for street use by itself, but with other mods it can start to add up. And for autocrossing every little bit helps. However, these filters are reusable and can last for the life of your car, and cost about the same as the standard filters, so you can save money in the long run.

Ram-Air Intakes/Filters

If you want more power, get one of the "ram-air" intakes. They replace the standard air filter housing and ducts with a system that promotes far better airflow. These are legal in the Boxster's SCCA "Street Prepared Category."

There is now a "ram-air" filter/intake setup available from Powerflow. It features a long tube from the intake manifold terminating in a conical air filter in the same location as the stock filter housing -- behind the left-side intake grille (the tube is the orange-yellow tube seen in the photo, the filter is dark red and is seen in the upper-right corner). A frequent poster on the Boxster Racing Board installed one and did before/after dyno tests. It resulted in an impressive 14 horsepower and 12 lbs/ft torque gain. This was on top of power he'd already gained from installing a "Danske" muffler (1-800-632-2743). I think this is entirely possible, based on my past tests of these types of intakes on my wife's Nissan Maxima. It also resulted in an increase in noise... that throaty, deep, gasping type of sound typical of low-restriction intakes.

Update: Another Boxster Racing Board poster also performed dyno tests after installing a Powerflow intake. He reported a smaller 6 hp improvement on his website. Hard to say which is more representative, but it certainly does look like the Powerflow intake helps to some degree.

There is also a unit similar to the Powerflow available from MSDS. Don't know any additional details other than what's at their site yet.

   
Powerflow horsepower graph printout (measured at the rear wheels). Powerflow torque graph printout.

Large-Bore Throttle Bodies

The throttle body is located between the engine and the air filter housing. It controls the amount of air that is allowed into engine. It includes throttle plates that are controlled by the gas pedal. By enlarging the throttle body internally, more air can pass into the engine thus allowing more power, especially at high rpms.

This is a more complicated modification that involves removing the standard throttle body, machining its inside intake passages larger, and often installing larger throttle plates. The downside of this modification, though less of an issue with a modern engine like the Boxster's, is that the car's low-end power is often reduced from the standard levels. Some manufacturers fabricate large throttle body kits, but none is available for the Boxster at present. So if you want to try this, you should contact a reputable machinist, such as those who advertise in PCA's Panorama magazine.

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