The problem with modifying the camshafts is that when you shift the power band from a low or mid range band to a higher band, the idle can be adversely affected. Slight power band shifts will yield only minor, if any, idle problems, but will only offer minimal power improvements. The more power you expect to get from a camshaft, the more problems you can expect to encounter, eventually leading to major problems with vacuum controlled accessories, such as the power brake booster. The engine will not create enough of a vacuum for the brake booster to function properly.

Second generation Probes have direct fit 'drop-in' camshafts from J-Spec engine which can improve top end power, without much of an idle change. Although there aren't any major companies offering performance camshafts for Probes, many performance engine shops in your area may be able to create custom camshafts for any application.

The Positive Crankcase Ventilation (PCV) system relieves the pressure in the cylinder head caused by a pressurized crankcase. Older engines use to vent these fumes into the atmosphere, but due to the EPA and emission regulations, newer engines are designed to vent the fumes into the intake system to be burned up along with the air and fuel mixture. The problem with this is that the crankcase fumes contain vaporized oil. This mist settles on anything in its path and coats the entire intake manifold with an oily film as well as enters the combustion chamber with the air/fuel mixture. When the piston rings begin to wear, combustion pressure increases blow-by considerably. This can end up causing your car's emissions to worsen and result in failure of emission tests. As the oily film builds up, a substantial decrease in performance will occur, including engine problems such as low idling and stalling.

Many Probes with over 100,000 miles on them suffer from excessive blow-by. Although you can opt for the breather filter addition procedure (see Do It Yourself Upgrades) for a simple low-cost way to keep the fumes and oil from entering your intake system, they can be illegal in many states due to vehicle emission codes. The best legal option are catch cans. They attach between the PCV valve and the intake manifold to filter out oil before it reaches your intake system. This keeps your intake system cleaner. The only requirement is that you empty the tank occasionally as normal maintenance.

As compression and horsepower increases under turbocharged and supercharged applications, head gaskets can become weak and fail. Standard head gaskets are usually made of layers of material such as steel, carbon, and asbestos. A seal is made when the cylinder head is torqued down and the head gasket is squished.

Copper head gaskets are solid and always keep their shape. Even under extreme compression, copper head gaskets will maintain their integrity. Since copper head gaskets do not squish during the cylinder head torquing, they can be reused over and over again. As long as they are properly installed, they will last the life of your car.

The only real problem that can occur with copper head gaskets are leaks. Before installation, the engine block surface and cylinder head must both be milled perfectly flat. Since copper head gaskets do not squish to create a seal, any imperfections can result in a leakage of oil, coolant, or air. Proper preparation will add considerably to the cost of this upgrade.

Although locating a direct fit copper head gasket may be difficult, most shops and companies that offer them for other engines are usually willing to work with custom applications.

When an engine is built at the factory, the crankshaft is balanced in line with the pistons for smooth engine rotation. Although it's balanced closely enough, there is a wide enough tolerance that more horsepower is lost during the rotation then there needs to be. When upgrading an engine, this lost horsepower can be more evident. Having each piston balanced so each are perfectly equal in weight, then balancing the crankshaft for the pistons using a strict tolerance, will allow the engine to run considerably smoother. The smoother the engine can run, the less horsepower is lost from the rotation. This also greatly increases engine life, since less stress is being placed on the bearings.

It's also important to have the engine balanced when replacing the pistons. If you replace the pistons with a lighter or heavier set of pistons, engine rotation can be adversely effected and engine life can be considerable reduced.

A cheap alternative to expensive mounts would be using two screw-type hose clamps in a cross pattern over each stock mount. Tighten the clamps to how restrictive you want the engine's movement. The tighter the clamps, the harsher the vibration will be, so again, this is only recommended for track use only.

The most popular engine upgrade is the Japanese spec engines straight from Japan. These engines are basically the same as their US brothers, but instead they're designed for racing without the EPA controlled guidelines. The KLZE is the Japanese version of Mazda's KL03 2.5L V-6 engine found in 2nd generation GTs. Swapping the stock V-6 with this engine will bring you straight to 200hp without any other modifications. A nice place to start. For 2.0L 4-cylinder second generation Probes, there's the FSZE engine which will produce about 170hp, up from 118hp of the stock Probe engine. The only problem with these engines are that they're technically not legal for street use.

Forged pistons are a must for heavily modified engines. When increasing the first generation's turbo to over 15psi, or adding nitrous or forced induction to a second generation Probe, forged pistons are highly recommended. Without them, you can do major damage to you're engine.

Some kits will allow you to install larger filters or dual filters for increased flow and better oil filtering. If you can find the room, this could be a considerable improvement with less engine wear due to small particles.

Cylinder heads are designed with valves that are precisely sized for optimal air flow into the cylinder. However, when increasing the cylinder's size or when supercharging or turbocharging an engine, the valves may not offer the optimal flow and can cause a bottleneck.

On stock naturally aspired engines, the increased valve size will offer minimal to no increase in air flow at all. This is because the cylinder is already pulling in and filling the cylinder will all the air it requires. However, increasing the size of a valve and enlarging the valve seat can improve air flow into the engine when a cylinder is overbored to a larger diameter.

On stock turbocharged engines, increasing the valve size can offer some improvement in air flow into the cylinders. This is particularly true on the first generation Probe's 2.2L engine. The non-turbo engine uses 32.5mm intake valves that are precisely matched to the cylinder's need for air. The problem here is that the turbocharged engine uses the same sized valves, even though the air flow is drastically increased as a result of the turbocharger. Increasing the valve size on 2.2L turbocharged engines will offer a mild improvement in air flow. As boost is increased on these engines, oversized valves become more valuable.

The same is true for 2.0L and 2.5L engines when turbochargers and superchargers are added. Air flow is drastically increased and the factory sized valves can no longer pass enough air to the cylinder with the amount of air that the turbo or supercharger is prepared to supply it with.

One particular downside is the possibility of valve masking as a result of there not being enough space for larger valves. Larger valves can open too close to cylinder walls which can hinder air flow into the cylinders.

The radiator is the core of the engine's coolant system. It dissipates the heat that the coolant absorbs from the engine. The Probe's stock radiator is quite large and does a pretty adequate job of keeping the engine cool. However, the construction is somewhat poor. All Probes have radiators that are designed with aluminum cores and plastic tanks. On first generation Probes, these tanks are situated on the top and bottom of the radiator. On second generation Probes, these tanks are on either side of the radiator. There are two main problems with these plastic sections. First, plastic is a poor conductor of heat. Even though the plastic takes up a small percentage of the overall area of the radiator, barely any heat can be dissipated though it. Second, the plastic to aluminum connection is a common failure point. Although the stock units often last over 100,000 miles, 95% of the radiator failures I've seen were due to the weak plastic to metal bond.

Upgrading to an all-aluminum radiator would offer minimal cooling gains, but would last much longer under more grueling conditions, such as on the track or in cold climates where the frequent use of the car can cause continued heating and cooling of the radiator.

Upgrading to a more performance oriented radiator can cool your engine even more, reducing heat wear and damage significantly. These radiators are usually only slightly larger, but are better designed to offer more surface area for more efficient cooling. The downside is the excessive price tag of these units. There are currently no direct fit racing radiators available for the Probe, so custom designing is the only option.

One thing to remember is that the intake manifold is cooled by the coolant as well. Decreasing the coolant temperature would also decrease intake air temperatures enough to provide a slight increase in horsepower.

Standard cylinder head valves are designed with a 3-angle valve seat. The valve seat is ground to three different angles... 30°, 45°, and 60°. This is a quick, cheap design that any shop can easily repeat during a valve job. Some shops offer 'performance grinds' that will grind the seat at 44°, leaving a 1° difference between the seat and the valve. All this really does is shorten the amount of time it takes for a valve to break in and doesn't have anything to do with performance.

A 5-angle valve seat is when a shop grinds two additional angles into the seat at 37.5° and 52.5°. This improves the air flow into the cylinder by offering a smoother path past the valve. Any shop that can do a standard 3-angle grind can do a 5-angle grind for an additional cost.

A radiused valve seat is when the valve seat is ground to a smooth curve. This maximizes air flow into the cylinder head by keeping the path past the valve as smooth as possible, even beyond that of a 5-angle grind. The problem of radiused valve seats is finding a shop that can do it. Only a very small number of shops are equipped to do such work.

Overall, horsepower is increased only slightly. This makes it a very impractical upgrade when done alone. However, it should be kept in mind when you get a valve job or send the head out for other work.