The intake system is the key to engine power. The more air you can get into the cylinders, the more horsepower the engine will produce. The key to an optimal intake system is giving the engine at least all the air it requires for most horsepower throughout the rpm range. This requires keeping the intake vacuum at a minimal with the least restrictions so there is no loss of power at high rpm when the engine needs the most air. The key to a perfect intake system is feeding the cylinders all the air they can handle to get the most horsepower from the engine. The perfect intake system will not necessarily have the highest pressure rate, but rather no vacuum present anywhere in the intake system so the engine will always have all the air it requires for the best power throughout the entire rpm range.

When upgrading your intake system, remember that cooler air is better. Click Here for more information on cold versus hot intake air.

Key
Pros: The benefits of a particular upgrade.
Cons: The down side of a particular upgrade.
Cost: Approximate price range based on numerous quotes and price sheets.
HP Gains: Estimated increase in horsepower you can expect from a particular upgrade. Not necessarily peak horsepower.
Manufacturers: Examples of particular companies that sell a particular upgrade.
Availability: Which Probes the upgrade is for.

Contents
Air Ram/Cold Air Intake
Boost Controller
Bypass/Blow-Off Valves
Cone Air Filter
High-Flow Air Filter
Intake Manifold Thermal Insulators
Intake Supercharger
Intercooler
Intercooler Piping
J-Spec Intake Manifold
Nitrous Oxide
Supercharger
Throttle Body
Turbocharger
Turbocharger Upgrades
Twin Turbo

Air Ram/Cold Air Intake
Stock air intakes are designed with two ideas in mind...  conservative placement and EPA guidelines (yes, the EPA has guidelines for intakes too). Intakes are usually placed high away from ground water and tucked away to keep foreign objects from entering them. Air rams extend or replace stock intakes in order to bring them into the open. The normal stream of air that's around the car is forced into the intake... the faster your car moves, the faster the air is forced into the intake. This improves horsepower ratings at high RPM when the stock intake can't feed the engine enough air.

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.

Personal Experience: I installed a custom air ram on both my '89 LX and '91 GT. The LX had a noticeable improvement in power, but the GT's turbo is what benefited the most. I dropped approximately .2 seconds of my 0-6 and 1/4 mile times, and there's a big difference in power over 75mph.
Pros: Increased air into the engine, increased high RPM horsepower.
Cons: Increased dirt and water onto air filter.
Cost: $10-$200
HP Gain: 5-10hp
Manufacturers: HKS, Hotshot, K&N, PaceSetter, RS Akimoto, Weapon R
  Availability: Second generation, otherwise require custom work
 

Boost Controller

 

Boost controllers allow you to bypass the preset boost level and adjust it to a higher level. The first generation GT has a boost of 7.3psi and an overboost of 9.3. Increasing the boost level to 10 or 12psi will allow an instant increase in horsepower. The GT's computer will cut the fuel at 15psi, but it's not recommended to go any higher than that anyway without forged pistons. 

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.

Personal Experience: I installed a GReddy PRofec B boost controller in my '92 GT. The kit was basically a universal installation and included everything required to do the install by yourself. Installation was very easy, but the hardest part was finding locations for both the controller unit and the new solenoid. It has two settings for low and high boost which are selectable on the fly. It also has a balance control for adjusting out any overboosting problems you may encounter.
Pros: Adjustable increase in horsepower.
Cons: High boost amounts can damage engine.
Cost: $300-$600
HP Gain: 5-50hp
Manufacturers: A'pexi, GReddy, Hallman, HKS, TurboXS
  Availability: First generation GTs
 

Bypass/Blow-Off Valves
Blow-off and bypass valves are crucial to a turbo's life span. When decelerating or between shifts, the throttle body plates close. If the plates close immediately after heavy acceleration, the boost air gets trapped and pressure forces it back into the turbo. This can be very destructive to a turbine. Blow-off and bypass valves keep air from reentering the turbo by relieving pressure in the pipes.

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.

Personal Experience: Currently looking into a GReddy Blow-Off Valve.
Pros: Increase turbo life, quicker boost response.
Cons: No direct fit valves, stability problem of blow-off valves
Cost: $100-$300
HP Gain: None
Manufacturers: Greddy, HKS, TurboXS
  Availability: First generation GTs
 

Cone Air Filter
Cone air filters have much more surface area than standard drop in filters. This increases air flow into the intake system. The down side is that the stock air box must be removed to fit the new filter. Without the stock air box, the only air that enters the intake is the hot engine air. The horsepower gains from increased air flow is overshadowed by the loss of horsepower from hotter intake temperatures. Air temperature in the intake can increase as much as 100 over the stock air box temperature. Considering for every 10 you lose about 1% of horsepower, that's about a 15hp drop.

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. 

Personal Experience: I'm sticking with the K&N and air-ram combo.
Pros: Greater increase in air flow.
Cons: Increased intake air temperature.
Cost: $50-$150
HP Gain: 1-3hp
Manufacturers: AMSOIL, AutoPhysics, HKS, K&N, Tenzo
  Availability: All
 

High-Flow Air Filter
The OEM type drop-in filters are usually made of restrictive paper. High-flow replacements are made of a cloth or sponge-like material that allows better flowing of air. This increases the amount of air that can enter the engine and with less effort.

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.

Personal Experience: A K&N filter was the first upgrade for my LX. Not much noticeable gains in power, but the deeper, slightly louder engine sound tells me the engine is getting more air. Also bought one for my '91 GT.
Pros: Increased air flow, increased horsepower at high rpm.
Cons: None.
Cost: $20-$50
HP Gain: 3-5hp
Manufacturers: AMSOIL, HKS, K&N
  Availability: All
 

Intake Manifold Thermal Insulators

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.

Personal Experience: After searching for some time for thermal insulators for my '92 GT, I decided to make them on my own. Testing showed improvements from 20°F to as much as 35°F. I can definitely feel the improvement in performance from the insulators... the lose of performance after my GT warms up is minimal now.
Pros: Reduced intake air temperatures.
Cons: Installation.
Cost: $105
HP Gain: 3-5hp
Manufacturers: Performance Probe
  Availability: First Generation 2.2L
 

Intake Supercharger
Turbos and superchargers do a great job of drawing in the air from the middle or end of the intake system, but this leaves a considerable vacuum at the beginning of the intake system. The optimal turbo or supercharged system will have all the air in requires, and no vacuum at the air sensor. Intake superchargers are electronic blowers that force air in at the beginning of the intake system, reducing or eliminating the vacuum at the air sensor.

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.

Personal Experience: Looking to incorporate it into my intake system sometime in the near future.
Pros: Maximizes intake airflow.
Cons: May cause lean air/fuel mixture, installation may require custom work, price.
Cost: $300-$650
HP Gain: 3-7hp
Manufacturers: e-Racing
  Availability: All
 

Intercooler
The intercooler is an important part of a turbo system. As pressure rises in the intake manifold, temperature also rises. The overall heat in the engine compartment can increase the temperature of the intake air even more. Anyone who's driven hard on cold days as well as hot days knows cooler air provides more power. You can expect to lose 1% of horsepower for every 10 the temperature rises over the outside air temperature. That could be as much as 15 horsepower. An intercooler is like a small radiator for intake air that allows it to cool. Although it can't cool the air completely, an intercooler can help you regain a few horsepower.

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.

Personal Experience: Currently looking into.
Pros: Cooler air entering the engine providing extra horsepower
Cons: No available direct fit kits, drop in boost pressure, lowered boost response.
Cost: $750+
HP Gain: 2-15hp
Manufacturers: HKS, Stillen
  Availability: First generation GTs
 

Intercooler Piping
The same press bent style of piping that hinders performance in a stock exhaust system creates restrictions in the intake of a turbocharged engine as well. Unlike a normally aspired engine where air goes from the air box straight into the throttle body, a turbocharged engine has many feet of extra piping that the air must travel through to get to the intake manifold. Air must travel from the air box to the turbo, then out into the intercooler, then finally into the throttle body. The small, press bent pipes increase restrictions in the intake system and raise the temperature of the air entering the cylinders. Mandrel bent piping will allow a less restrictive airflow traveling throughout the system, reducing backpressure, and thus reducing the turbo's work load.
Personal Experience: Currently looking into custom intake pipes.
Pros: Increases airflow throughout intake system, lower intake temperature.
Cons: Cost
Cost: $300-$400
HP Gain: 2-3hp
Manufacturers: GReddy, HKS
  Availability: First generation GTs
 

J-Spec Intake Manifold
J-Spec engines have become popular upgrades recently. J-Spec engines are engines from Japan, pulled out of Japanese cars. These engines have much more power than the U.S. versions, mostly due to excessive U.S. regulations. For those who want the benefits of J-Spec engines, but don't what to swap the entire engine, many importers are offering certain parts separately from the engine.

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.

Personal Experience: None.
Pros: Makes considerable airflow improvements, 2.0L gets VRIS.
Cons: May not be legal in certain areas.
Cost: $500-1000
HP Gain: 10-15hp
  Manufacturers: Corksport
  Availability: Second generation
 

Nitrous Oxide
Nitrous oxide, also known as N2O or laughing gas, is a quick and relatively cheap way to add a lot of horsepower to your engine. It adds horsepower in two ways. First, when nitrous oxide is released into the intake system, it contains almost 2 times more oxygen than air,  allowing more fuel to be burned in the cylinders, creating a lot more horsepower. The more nitrous oxide that's released into the system, the more horsepower can be made. The second way it increases horsepower goes to an important principle of the intake system: colder air is better. For every 10 you drop the air temperature entering the cylinders, you'll get about a 1% horsepower increase. Nitrous oxide can drop the air temperature by 60 to 80, which could add about 10 to 13 horsepower to a second generation GT. Very impressive results either way.

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.

Personal Experience: Stories of blown pistons and spark plugs, safety hazards, and love for my car have kept me clear of this option.
Pros: Massive boosts of power obtainable. 
Cons: Can be destructive to stock engines, not for engines with high miles, safety concerns.
Cost: $300+
HP Gain: 25-100hp
  Manufacturers: Nitrous Oxide Systems, Venom Performance
Availability: All

Supercharger
A supercharger is a type of air induction system that, like a turbo, forces more air into the engine's cylinders. A supercharger is a fan that's belt driven along with the AC and alternator. As the engine spins faster, the blower spins faster forcing more air into the engine. With more air entering the cylinders, more horsepower can be made.

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.

Personal Experience: None
Pros: A lot more horsepower, safer than nitrous oxide
Cons: Quality of some fabricated supercharger setups, installation
Cost: $2500-$5500
HP Gain: 50-125hp
Manufacturers: Thomas Knight Turbos
  Availability: Second generation GTs
 

Throttle Body
The throttle body is the gateway for air entering the intake manifold. The throttle body regulates how much air can enter the intake manifold which enters into the engine's cylinders. This directly controls engine speed. Boring out or getting an oversized throttle body will allow more air into the engine's cylinders, creating more horsepower. The problem is that the additional air passing through the throttle body is unaccounted for, causing the air to fuel ratio to run lean. Combining this upgrade with a fuel regulator will provide the optimal usage.
Personal Experience: Currently looking into.
Pros: More air entering intake manifold, increased horsepower during midrange to high RPM.
Cons: Lean fuel to air mixture.
Cost: $150-$300
HP Gain: 5-10hp
Manufacturers: None
  Availability: All, 1st gen V6 owners may need to get Taurus 3.0 part
 

Turbocharger
A turbocharger is a type of air induction system that forces more air into the engine's cylinders. As the exhaust gases exit the cylinders and go through the exhaust manifold into the exhaust system, it first passes through one side of the turbocharger. As it passes, it causes the turbocharger's fan to spin, which also spins the fan on the intake side of the turbocharger. The spinning of the intake fan forces more air into the intake manifold. With more air entering the cylinders, more horsepower can be made.

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.

Personal Experience: None
Pros: A lot more horsepower, safer than nitrous oxide
Cons: Quality of some fabricated turbo systems, installation
Cost: $2000-$4000
HP Gain: 25-125hp
Manufacturers: Thomas Knight Turbos
  Availability: Second generation
 

Turbocharger Upgrades
A turbo upgrade is basically just a larger turbo capable of forcing more air into the engine with less effort. The only turbo upgrade available is obviously for the first generation GTs since they were the only ones to have a turbo. Thomas Knight Turbos makes a turbo upgrade kit for first generation GTs. Positive effects will be minimal on a stock computer program, but are more evident with either a reprogrammed computer or a boost controller. Negative effects will include lowered boost response, and less boost power at lower engine speeds.
Personal Experience: I purchased a Thomas Knight Turbo upgrade for my '92 GT's turbo. The TKT turbo upgrade is basically a Garrett T3 turbocharger fitted to a Probe's turbo exhaust housing.
Pros: Higher induction capacity over stock turbo
Cons: Less boost response, less boost at lower rpm.
Cost: $500-$1000
HP Gain: 5-10hp
Manufacturers: Thomas Knight Turbos
  Availability: First generation GTs
 

Twin Turbo
As a turbo setup is one of the top upgrades you can get for you Probe, a twin turbo setup would be top-of-the-line. Single turbocharger systems do a great job of forcing air into the engine, but as you increase the size of the turbo, the turbo will take longer to spool up, losing low end boost power. Twin turbo's use to two smaller turbos instead on one large turbo to improve spool up, while offering high end boost power. With a twin turbo system, you get the low spool up time of a small turbo, with the large boost levels of a large turbo.

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.

Personal Experience: None
Pros: Higher induction capacity single turbo, safer then nitrous oxide.
Cons: Quality of some fabricated turbo systems, installation, can be too much for the engine to handle.
Cost: $5000-$8000
HP Gain: 100+hp
Manufacturers: Thomas Knight Turbos
  Availability: Second generation GTs
 

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