Cold air intakes differ from air rams in that they aren't designed to force air into the engine. They replace the stock air filter with a cone filter, but instead of the filter feeding off of the hot engine compartment air, the cold air intake extends down to the bottom of the engine compartment and supplies the filter with fresh air. Although better than the stock set up, this is not as effective as an air ram.

The two generations of Probes have different set ups for how air gets to the air box and filter. 1st generation Probes have a plastic tube that extends from the air box into the left fender. The opening of this tube is directly behind a support that connects the fender, front bumper cover, and frame. This design makes it almost impossible for foreign objects to enter the intake, but also makes it very hard for AIR to get in. I haven't seen any air ram kits for the Probe, but with a couple of feet of air duct, a custom designed air ram can be better and much cheaper.

The 2nd generation Probe has a less restrictive setup, but benefits greatly from an air ram. It has a tube that runs from the air box through the engine compartment just under the hood, and to an opening just above the radiator. Most air ram kits cost over $100 and usually aren't better than anything you could build for $10.

Manual boost controllers are simple knobs that allow you to adjust the boost through an approximate range. A more accurate boost gauge is highly recommended with a manual controller. An electronic boost controller costs more, but is very helpful when adjusting the turbo's levels. Most include an integrated boost gauge that allows you to better fine tune the boost levels.

Before increasing your car's boost level, check the engine's condition and compression. Increasing the boost on worn engines can cause damage.

The first generation Probe GT's stock turbo system has a bypass valve that relieves the pressure during deceleration by bypassing the turbo. The valve is located just after the turbo's outlet and sends excess air back into the tube connected to the turbo's inlet. Although stock valves function well, they tend to be unreliable at higher boost levels. Aftermarket bypass valves are more reliable at higher boost levels and are less likely to leak precious boost at lower boost levels.

Aftermarket blow-off valves differ from bypass valves, as they expel excess air out of the intake system, rather than sending it back into the intake system at a different location. This provides a slightly quicker response of boost... useful when the throttle plates closed as a result of shifting gears, but this is the only benefit of blow-off valves over bypass valves. Blow-off valves are more popular then bypass valves, simply due to the noise they make. When the air is expelled out of the system during deceleration, the air makes a 'whoosh' sound. Unfortunately, since the air flow meter had already accounted for the air entering the intake and does not register the fact that the air is being expelled from the intake, the ECU still thinks that air is in the pipes and injects the appropriate amount of fuel into the cylinders. This will cause a richening of the fuel/air mixture and can cause stalling. A heavy downside, but people must have their noises.

In combination with a cold air intake that can send fresh air into the engine compartment, colder air can enter the filter, but it's still limited by the underhood temperatures. 

Since these filters are made of a stronger material than paper, most high-flow replacement filters are washable, allowing a lifetime of use. This makes their price tag more acceptable.

Most people notice that when an engine is still cold, their cars seems a bit more 'lively'. When the engine warms up, the car seems just a bit duller performance-wise. This is due to the fact that the intake manifold becomes hot and warms the intake air considerably, robbing you of 2-3 horsepower. One option would be to lift the rear of the hood an inch or two to allow more air to circulate, but this can have a negative effect on appearance.

Another way to keep the intake manifold temperature down is to stop the problem at its root. Much of the intake manifold's heat is conducted from the engine block. The only thing that's between the intake manifold and the engine block is a gasket 1/32" thick. Heat easily conducts through this seal, heating the intake manifold and the air that enters the engine. Thermal insulators are basically extra thick gaskets made of a material with a very low thermal conductivity. This effectively reduces the amount of heat that's transferred from the engine block to the intake manifold. Thermal insulators won't add power to your engine, however they will help keep the drop in power experienced after the engine warms to a minimum. A temperature drop of 20° to 50° can be expected, which could yield 3 to 5 horsepower.

The main downside to this upgrade is the installation. Although kits can include several different parts to make installation as easy as possible, such as longer studs and bolts, brackets, and fittings, installation isn't always simple.

The e-Ram from e-Racing offers an electronic supercharger that could fit almost any vehicle. At wide open throttle, the blower forces air into the intake system which keeps the engine from starving for air.

The problem with these devices is all the extra air that's being forced in. Without an additional fuel management system or an upgraded fuel system, the air/fuel mixture can run somewhat lean, limiting improvements that result from the increased airflow.

The stock intercooler for the first generation Probe GTs is small and, like most other factory parts, conservatively designed. Getting a larger intercooler will increase the surface area allowing the air to cool better. Horsepower gains depend on your overall turbo and intake set up. If everything else is stock, gains will be minimal with a drop in boost pressure and response. If you have a high flow air filter and air ram, gains will be more noticeable. You will benefit most from a larger intercooler if you have a high flow filter, air ram, and you increase the turbo boost.

The 2.5L V-6 J-Spec intake manifold has a few differences from its U.S. counterpart that allows more air to enter the engine. The angled throttle body and larger ports allow considerable better airflow, resulting in improved horsepower, especially at higher rpm.

The J-Spec version of the 2.0L 4-cylinder's intake manifold makes an even larger improvement over it's U.S. counterpart. The 2.5L makes a lot of horsepower due to the Variable Resonance Induction System. This system opens valves at higher rpm to allow more airflow into the engine, but closes them at lower rpms to lengthen the runners and provide low end torque. The problem is that the VRIS feature is not available on the U.S. 2.0L. The J-Spec manifold, on the other hand, has the VRIS feature, giving it a considerable boost in power, while retaining low end torque.

You should check inspection laws in your state to make sure this manifold is legal before purchasing.

Unfortunately, nitrous oxide comes at a large price. First, and foremost, is the destructive side effects... stock engines aren't designed to handle that enormous power that comes from nitrous oxide. Aside from increase engine wear, piston damage, cylinder head damage and blown head gaskets are a common result. A stronger head gasket, forged pistons, and an upgraded fuel system is strongly recommended, if not required, driving the price of a nitrous oxide system up substantially. A nitrous oxide system on a four cylinder engine is not recommended. Also, nitrous oxide systems can be extremely dangerous. If not installed correctly or a low-quality system is installed, the nitrous oxide bottle can become a bomb, capable of completely destroying your car.

Nitrous Oxide Systems and Venom Performance currently makes nitrous oxide systems for all Probes.

Currently, there is only one place where you can get a direct fit supercharger kit for your car and they're only available for the second generation Probe GTs. These kits, created by Thomas Knight Turbos, include everything you need to install the supercharger, and yields pretty impressive results. Unfortunately, since it's not a factory manufactured kit, quality is questionable.

The biggest problem with these is the installation. It requires a lot of work and relocation of the battery. You'll need to be very fluent with your car to get through it yourself.

Currently, there is only one place where you can get a direct fit turbo kit for your car and they're only available for the second generation Probe 2.0L and 2.5L engines. These kits, created by Thomas Knight Turbos, include everything you need to install the turbo, and yields pretty impressive results. Unfortunately, since it's not a factory manufactured kit, quality is questionable.

Anyone with a first generation non-turbo 4-cylinder looking to add the first generation GT's turbo to your engine should reconsider. Although the engines are the same, most of the components differ, making this an extremely costly and time consuming job.

The biggest problem with these is the installation. It requires a lot of work and relocation of the battery. You'll need to be very fluent with your car to get through it yourself.

Thomas Knight Turbos offers a twin turbo kit at request, but it's a custom order. Installation is not for the novice mechanic, and it's strongly suggested that you do some major maintenance work on your engine before installing a twin turbo kit.