This is a simple overview of the basics to get more power out of the majority of engines out there. not all points will apply to all engines but in general the following is true.

Breath Easy: The idea here is to remove restirction causing parts or connections in the intake and exhaust system. All engines are essensally an air pump... so Air in and Air out. The less effort needed to get air processed the more power the engine can get to the ground.

-Air Intake system:
*Cone Filter K&N or equivalent. This will allow more air to enter the system. Remember to keep the intake air cool though. Additional air is important, but if it is hotter it will be come less dense and not supply any more oxygen then your factory system... and possibly less. This results in a decrease in power. Further more, pcms (the engine computer) will start reducting spark timing when the air intake temps increase. this directly reduces power.

*Replace rubber-flex hoses in intake with smoothly bent tubes or adapters. This reduces restricitons in the intake.

-Port match and Polish Intake pieces. (Mass Air Flow sensor, Throttle Body, Intake Manifold, Heads intake and exhaust) This reduces friction in the intake and exhaust because most factory systems have mismatch areas that can be off a considerable amount. Head work is the most expensive of these, but will be the most rewarding.

-Exhaust System (Headers, Down Pipe, Cat Back, High flow mufflers) Factory systems usually are restrictive. Much can be gained from switching out parts or consulting individuals that have experience with your particular engine. On the 3.4 DOHC the cat is said to be restrictive. I personally have seen my cat after I had done a highflow cat and light weight exhaust system, and the factory cat is fine. The stock DOHC has a 2.5" down pipe, although not mandral bent, it flows well and is stainless steel. Also the system after the cat is press bend and actually less then 2 1/4 inch in dia. By installing a new Catalist and new mandral bent exhaust, you can free up some otherwise lost power. You might have heard you need "backpressure" this is a myth! The myth is actauly talking about scavenging. Scavenging it using one exhaust pulse to pull the next... and this is what makes Tq. If your exhaust flows too fast, (say a 3-4" exhaust on a NA car) your first exhaust pulse will leave the system before it gets a chance to pull the next one. This will kill your TQ but help make HP. the key is to balance the two. (refere to my curret system for ideas)

-Cam shafts and Cam timing: These control when the intake and exhaust valves open and close. By Changing the cam timing you are able to get more air in and out of the engine. this is because the cams directly control when airflow occurs in the engine.
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Keep'er Cool: The cooler the engine, the more power it will produce.

-Lower temp Thermostat This will help keep the engine oil at proper temperatures and prevent additional heat soak (heat warming intake temperatures) For the lightly mod'd engines a 180* is recommended. This lower Tstat will also help to eliminate engine KR (Knock retard) KR is where the engine detects detonation and pulls fuel and spark timing to keep the engine safe. But this reduces power in the process. I you are able to scan the engine and discover you have KR a lower temp TStat might help.

-Fender Well Intake / Cold Air Intake. These will allow the engine to breath cooler air then it normally could from the engine bay. Remember cooler = denser air = yields more power.

-Synthetic Oil. This will lower internal friction from engine and reduce operating temperatures. Also it lasts longer and doesnt break down under high temp or high RPM like dino oils.

-Radiator Fan controller. Allows both fans to go on at once, ability to run them when the engine is off (for in staging at the strip), and to adjust the fan activation point to adjust for a new lower temp Thermostat.

-Throttle Body Coolant Bypass. Most factory cars run hot engine coolant thru the Throttle body to prevent ice from forming in the winter. This also increases your intake temperature, which you are trying to lower. If you are in a warm climate or plan on using your car for track only. This is one of those mod's that you might not feel the increase in performace, but it is cheep easy and makes removal of your TB easyer for the future.

-Larger Cooling devices. Radiators, Aux Transmission cooler, Aux Oil Cooler, and Intercooler if you are running a form of boost IE Turbo or Supercharger. Caution! Over cooling of engine coolant can cause the block to crack or excessive engine ware.
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Feed the Beast: Basic Idea? Your probably giving your engine more air, so give'er more fuel.

-Octane Use the lowest octane fuel that does not cause your engine to knock. (the only way to know if your engine is not knocking is to use a OBD scan tool... some people believe you should be able to hear Knocking... prob is if you are hearing the knock/detonation it is far too late... the sound is caused from damage being done to the piston or head) Higher octane rating does not mean the fuel is stronger or that it has more power. The rating is the fuels resistance to ignition from heat, such as carbon, hot spots, or pressure spikes. If your engine is knocking switching to a higher octane will help this.

-Air/Fuel Ratio Re-compute your fuel to air ratio with a Fuel/Air computer. Adjusting injectors, fuel pressure, pump, and lines to match new settings. This allows more or less fuel to be used. More fuel is not always the answer! Natrually aspirated engines tend to like AF ratios in the 12-13 range and Boosted motors tend to like 11-12 range. 12.5 is the AFR that generates the most power on gas...this doesnt mean it is best for a given motor.

-Power Adder NO2 will give the engine more kick when activated by supplying the engine with more oxygen either in the intake runner or in the fuel system (Dry vs Wet Nos systems) NO2 also cools the intake charge making the incoming air more dense. These systems put more stress on your engine. They systems are not recomended for daily drivers and it is recomend that then engine be rebuilt specificly for NO2 if you plan on running anthing over a 60-70 shot.
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Spark up: With more fuel and more air, it is harder for the factory ignition system to light off the Fuel Air mix. After market ignition systems will not only give more power, they will be more efficient and save you gas.

-New Plugs. Not all plugs are the same or work the same in all engines. Research what plug works best in your engine from other people. For the DOHC the AC Delco Rapid-fire plugs are viewed to be the best plugs for a stock to lightly modified engine. For further modification, NKG iridum plugs are an option. Identifying the correct heat range of a plug is most important. if your plugs are ashy and white this indicates that it was lean... and needs a colder spark plug and or additional fuel. if the plug is dark and has buildup on it, the plug was too cold and the deposits werent being burned off it. a hotter spark plug is adivsed in this situation as with removing fuel or advancing spark timing.

-New Ignition Coils. Coils with lower resistances and stronger spark will deliver more power to the spark plugs. Manufactures for the DOHC are MSD, Accel, Jegs, and Summit. We are luckey in that GM gave us a very good ignition system. the stock DIS (distributorless ignition system) is packed with plenty of power. the stock system has powered Grandprix into the low 10's and some into the 9's in the 1/4 mile. it is very unlikely that the system will need to be upgraded.

-Thicker Wires. Factory Wires are fine, but if you upgrade your Ignition system, you will need to get wires that resist outside inference and are better insulated to accommodate the higher voltage of the new system. again the OEM wires are more then enough for 80-90% of the modified cars. again many people retain the factory wires and have run well into the 10's and 11's with no issues.
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Take a load off: Instead of trying to make more power, try and recover it from parasitic drag by using light weight parts.
* anything that rotates takes a lot of power to spin when heavy.

-Empty the trunk. All the junk you many be lugging around is slowing you down and using extra gas. 100 lbs equals about 15 Hp. Just like the import crowd, you can pull out the trim panels, seats, carpet, spare and jack, and audio system :-X Also you can swap in lighter wheels/tires and body panels. Some engines have items like hoist hooks and brackets in the engine bay that dont serve a mechanical or safety roll. these can be removed.

-Under Drive Pulleys. Not only are these pulleys lighter cause of their Aluminum construction, they are a smaller diameter to reduce the load from the accessories. remember pulley sizes are basicly levers, just round.

-Lightweight flywheel. Not the best for a daily driver, but for track cars these can recover serious power. But arent as strong and are prone to cracking.

-Lightweight engine components. Pistons, Valves, and Lifters. These are esenial for making an engine withsand High RPM! With these you will need to rebalance the engine. By rebalancing the engine you will also gain more power and prolonging the life of the motor by reducing stress.

-Switching to electric Accessories. Such as an electric water pump, fans, or power steering. These reduce the load on the engine and are more efficent. Also removal of the AC system can shave off a few pounds too. But i would rather be a little slower then not have AC!

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Boost: Need i say more?
Any form of boost will give you more power when it is properly tuned. Turbos and superchargers are the main and to my current knowledge the only source of boost avalible to piston engines.

-Turbo's. These use pressure from the exhaust to spin/spool a fan/turbine that powers another fan/compressor to force-more-air/boost into the engine. As you read before More air needs more fuel so proper tuning is a must. But,this addtional Air needs creates more heat, and causes more stress to the engne. Additional heat also increase the chance of causing detonation which shows up as Knock which will either make the pcm reduce power or if power isnt reduced damage will result. Once a turbo is spooled, its output is kept in check by the use of a waste gate. turbos will quickly reach the max boost setting and then maintain it. this gate "wastes" additional exhaust gas when its setting is reached in order to limit the amount of boost created. Working with this is also something called a blow-off-valve or diverter valve. This also limits boost so that during a shift when RPMs are changed pressure can be vented so that damage doesnt occur.

-Superchargers. SC's differ from Turbos in that they are powered by a belt system off of the engine. By having the SC powered directly like this, throtle responce is near instant. This quick responce is why many car companys use SC instead of Turbos. Boost output is directly proportional to the RPM of the engine... As rpm increase boost will increase. Many newer SC's have what is called a BBV Boost Bypass Valve. This valve will open to vent pressure similar to the diveter or blow-off-valve on a turbo. the idea again is to limit boost. It also serves the perpuse on SC cars to alow the engine to use less fuel at low rpm's. with the BBV open the engine acts like an NA motor because the load on the SC is no longer present.

* both forms of boost come with many variables to consider. If you dont know what kind of turbo or SC you need consult experts to plan what your goals for ths system are and how best to aproach the project.