Replace the steering wheel with a smaller, sportier-looking and more grippy wheel from MOMO or a similar company (see Resources). Scions come with relatively large steering wheels, so replacing the wheel with an aftermarket one is a good first step. You will need a steering wheels adapter to allow the wheel to fit. Also, it should be noted that a smaller aftermarket wheel will not allow you to use the air bag, which many people consider an important safety feature.
Install an alloy or carbon fiber shift knob from a company like Sparco (see Resources 2) on Scions that are equipped with a manual gearbox. An alloy shift knob feels great on your palm and can also make shifting more effortless, particularly if it is a heavier knob. Most aftermarket shift knobs are held on with a series of set screws that run around the base of the knob and fasten the knob to the shift lever. Some will fasten in the same method as the original shift knob.
Upgrade the rubber pedal pads to alloy pedals, which provide more grip and look better. A set of alloy pedals for the gas, clutch and brake controls is relatively easy to install. They are either held on with clips or awith nuts and bolts, in which case you will need to use a drill and a drill bit to make holes in the existing pedals to bolt on alloy pedals.
Replace the original seats with aftermarket sport or racing seats from Recaro or Bride. Upgraded seats will offer superior bolstering over the stock seats, which will really come in handy if your Scion has been modified to accelerate, corner and stop faster than stock. Aftermarket seats require the use of seat adapters in order to be installed in a Scion, but these adapters are available from the seat manufacturers. Installing them is a matter of removing the original seats and bolting in the adapters and the new seats.
Install racing harnesses to complement the new seats. Multi-point harnesses look great and hold the occupants in much better than the standard three-point seat belts that come standard with the Scion.
Upgrade the lighting and the gauges. There are several accessories available that can help your Scion stand out from the crowd and make the interior a more pleasant place to be (or at least a cooler place to be.) The stock gauges can be swapped for more interesting looking gauges and lighting (see Resources). You can also install a multi-piece graphic set on the interior surfaces that will liven up the center console, dash and door panels.The Scion lineup is designed and made by Toyota specifically for the U.S. market. Only here can buyers experience the car's combination of youthful design, clever engineering and practicality. There are several Scion models available, including the xA, xB, xD and tC, but they all take equally well to tuning and modifying. The interior is one of the first areas that many owners modify first.