Making a vehicle's intake and exhaust system louder can be a simple process. Typical gasoline motors have their "exhaust note" set by the size and openings on the pipes that take in normal air and output exhaust gases. The average backyard mechanic can change the intake and exhaust volumes in about an hour.
Install a larger air intake. A gasoline engine is basically a large air pump, and increasing the width of the intake pipe will cause the pitch and sound of the motor to increase. Installing an intake snorkel will also improve the performance of the motor, and larger, open element filters increase the effect.
Drill holes in the muffler or tailpipe. This can have the most dramatic effect increasing a system's volume, because a muffler is designed to do just the opposite, or "muffle" the sounds of the engine. Several holes half an inch wide or larger can let out exhaust in many pitches or volume levels. The larger the holes, the deeper and more powerful the sound will be.
Add a tailpipe horn. Changes to how the exhaust exits the tailpipe can have the same effect different horn shapes do for musical instruments. A "trumpet" pipe, which simply bolts onto the existing tailpipe, can enhance the sound to incredible levels.
Install a wider tailpipe from the exhaust manifolds to the rear of the vehicle. Normal tailpipes are between one and two inches wide, and replacing them with three- or four-inch pipes will have a dramatic effect on the volume and pitch of the exhaust note. Cut the pipe in front of the catalytic converter and use an adapter to weld in the new one. It might be necessary to have a pipe-bending tool--some vehicles require special shapes to run the exhaust properly.
Cut off the tailpipe at the exhaust manifold. This is the most dangerous method, leaving the engine's exhaust open from the manifold back. Without any type of cat converter or muffler, the exhaust will be incredibly loud, almost deafening depending on the car.
