What is an engine?
To understand how power adders work, you need to get the fundamentals of engines down. For the sake of education, your engine is an air pump. It pulls in air, squeezes it and forces it out. Combustion is a byproduct of this, not the main focus of an engine. Injecting fuel into a hot air mixture and lighting that fuel produces the power to keep the engine pumping air, by means of vacuum. Of course, you can only pump so much air from a certain volume in the combustion area, and this is called Volumetric efficiency (VE).
An engine's VE is a calculation of the size of the engine, the compression ratio (CP or CR) of the engine's combustion chamber and the rotating assembly, the pumping losses (frictional losses, heat loss, etc.) and the speed at which the engine can effectively move this air. More technical details will follow on these specific calculations, but for now we'll keep it simple. The amount of air (Volume) your engine can move is Torque. How fast the engine can move that air (Velocity) is Horsepower. There are also two measurements of HP; BHP/WHP. BHP (Brake horsepower) is power calculated at the engine's crankshaft. WHP (Wheel Horsepower) is power calculated at the wheels.
Let's talk about how to make an engine RUN. You need 4 different things; Air, Fuel, Spark and compression. Let's delve a (little) bit deeper;
AIR: Remember how we talked about engines being air pumps? You can't run an engine without it actually pumping the air. Pull air in, push air out. MOVE THE AIR. The MORE air your engine can MOVE, the more TORQUE it makes. The FASTER it can move this air, the more HORSEPOWER it makes. With this in mind, the less restriction in the air system, the more air it can move, faster. There is science behind the most efficient design here, and this can become its own topic (See: intake and exhaust theory) but let's stick to basics. If your engine can't breathe, it can't make power. While we're here, know that air expands as it heats up, and contracts as it cools off. Colder air = Denser air = More air per specific area, so more power can be extracted because you can inject more fuel for the air and make more boom boom. So you want the coldest air possible entering the engine, and some people go to extremes to do this (see: Iceboxes for drag racing). Done.
FUEL: An engine pushing air through will make 0 power, and it will actually take energy to compress that air in the first place. That's why starting up the engine takes a lot of energy from the starter and draws a lot of amperage. Fuel is what provides the energy to keep the engine moving. If you time fuel delivery and quantity properly, an engine will run indefinitely (See: Rudolf Diesel's first Diesel Prototype engine). Let's skip specifics again, since this can become its own topic. Your fuel system has to inject the right amount of fuel per amount of air that the engine is pumping to run properly; Ideal gasoline Air-To-Fuel (AFR) ratio is 14.7 air molecules to 1 gasoline molecule (14.7:1). This is referred to as the Stoichiometric coefficent. At this ratio, the fuel will burn completely and produce the most ideal ratio of exhaust gases. IF your fuel system is injecting MORE fuel than this, you are RUNNING RICH. Likewise, if you inject less fuel than this ratio, you are RUNNING LEAN. Most people will call them rich, fat and happy, and lean mean explosion machine but the reality is, there are reasons to run different ratios and there's a huge list of factors that you need to consider for each situation. More in depth later.
Spark: Spark is the big difference between a Gasoline and Diesel engine. Diesel engines compress the air/fuel mixture to heat it up past its FLASH POINT (past a point where the fuel will spontaneously combust) while Gasoline engines artificially raise the operating conditions of the Air/Fuel mix past that point. Let's get one thing straight here, Sparks DO NOT IGNITE THE FUEL, they simply superheat the air in the immediate location around the plug to surpass the flash point. Spark plugs cause a spark (duhhhh) which is a flash of superheated Oxygen atoms in a plasma state. This plasma state is super hot, and it causes the fuel to spontaneously combust. The process spirals in progressive waves depending on the design of the plug, chamber, blah blah blah, details, physics, thermodynamics jargon. What you need to know is that your fuel heats up from the explosion fronts (created in shock waves) and it's a compound effect. You have something called a flame front, which is the outermost portion of the explosion and you need to time this explosion correctly to produce the most power and force against the piston and rotating assembly, and subsequently, produce the most torque. When the fuel ignites at the wrong time or not at all, you get abnormal combustion (many names to it depending on what's happening, like spark knock, engine ping, fuel knock, etc.) and this can AND WILL cause major engine damage. More on that later as well....
Compression: All of these factors are important, but what good is a leaking air pump? If you can't compress the darn air, then the explosion from the fuel and spark won't have enough force to actually drive the engine and make power. Your engine needs to have proper compression to make all of this power in a controlled environment. Every engine is different, but the rotating assembly design (pistons, rods, crank, etc) will dictate your Compression Ratio (CR/CP). This is another 3 topics on its own but the basics are; the higher the CR, the more force the explosion will produce, the more heat will be generated and the higher the torque of the engine. This also makes the fuel more volatile and so it will spontaneously combust without the spark plug in the form of pre-detonation, spark knock, etc. if not controlled properly. This is why high comp motors or FI motors run higher octane fuels (fuel that resists detonation better) and will <ON PURPOSE> lower CR sometimes. For all you BK1 3.8s, your stock CR is 10.5:1, and BK2 3.8s are 11.5:1. This means that for the BK1 3.8, your combustion chamber compresses the air/fuel mixture 10:5 times atmospheric pressure, and for the BK2 that compression is 11:5 times atmospheric pressure. For reference, ATMospheric pressure is 14.7Psi at sea level (and it gets thinner the higher up you go in elevation). Hint, hint: If you want to do a compression test, know your engine's operating CR, get the test kit hooked up to your spark plug hole and crank the engine with the ignition module relay and fuel pump relay disconnected, then measure the pressure. If your CR is 10.0:1 for example, look to hit 125-135Psi (147Psi is IDEAL and you will always have some pumping losses/seepage past valves, pistons, etc. so don't expect the exact number, 75-85% compression is a good number, and there are different pressures expected for cold engines, warm engines and before/after squirting oil into the cylinder to mimic running conditions - We can talk all day on specifics).
Now that you have more of an idea of how engines work, we'll get into the difference between a modification and a power adder. A MODification, is something that allows the engine to breathe BETTER. Think of it as eliminating a restriction (larger intake volume, free-flowing exhaust, etc.). Mods can only help the engine move as much air as it can physically run according to its VE.
What is a power adder?
Glad you asked! A Power adder is something that artificially forces an engine to make more power. This is not to be confused with mods that allow the engine to breathe better. Let's go more in-depth