3S-GTE: The engine in the 1991+ MR2 Turbo. In-line, 4-cylinder, 2.0 litre 16 valve turbocharged engine with TVIS.
BGB: "Big Green Book". The Toyota Repair Manuals for a particular model. aka "shop manuals".
ECU: "Engine Control Unit". Generic name for the computer that controls the engine, and other associated functions such as air conditioning, in modern cars. The ECU controls fuel and spark delivery to maximize fuel efficiency and power while minimizing pollution and controlling detonation. Toyota calls the ECU the PCME ("Powertrain Control Module Engine").
Fuel Cut: n. 1. An action taken by the ECU, in self defence. In response to a signal from the MAP (Manifold Absolute Pressure) sensor indicating that the boost has exceeded 12psi, the ECU immediately stops all fuel delivery at engine speeds above 3000RPM. The triggering of Fuel Cut is apparently a very traumatic experience for both car and driver. Resetting the Fuel Cut is apparently as simple as switching off and restarting the engine, although I have also been told that a circuit breaker must be reset manually. 2. The boost pressure at which ~ is triggered.
Heat Range (of spark plugs): The tip of a spark plug gets very hot. A spark plug that runs too hot will deteriorate quickly, and can cause detonation in the engine. A plug that runs too cold will "foul". A plug at the right temperature can clean itself of carbon and unburnt hydrocarbons, without triggering detonation. The length of the insulator determines the heat range of a plug; a longer insulator will run hotter because it holds the tip farther away from the head, which acts as a heat sink. In general, high-performance engines run colder plugs than ordinary engines do.
Stoichiometric: An air/fuel mixture is stoichiometric if there is exactly enough oxygen to completely burn all of the fuel, with none left over. The air:fuel ratio of 14.7:1 at zero humidity is stoichiometric. More fuel than stiochiometric is considered a "rich" mixture; less fuel makes the mixture "lean". A rich mixture burns cool and leaves carbon monoxide and unburnt hydrocarbons in the exhaust gases. A lean mixture burns hot and fast, and therefore creates more NOx.
Supercharger: An air pump that pressurizes the engine's air intake system. Positive displacement superchargers, such as the Roots type, provide a constant boost pressure at all engine speeds. Negative displacement superchargers, such as the centrifugal type, provide boost pressure only above a certain engine (impeller) speed. A turbine supercharger ("turbo") is a centrifugal supercharger whose impeller is spun by a turbine in the exhaust stream, and so enjoys the lowest parasitic drag of all supercharger types. Most other superchargers are run by a belt off the engine. Other uncommon drive mechanisms include hydraulic and electric.
Supercharging: To pack more air/fuel mixture into a cylinders than the engine could draw in itself, is to supercharge the engine. A "turbo" is in fact type of supercharger (a "turbine supercharger"). There are other types of superchargers, some similar to a turbo and some quite different. Inertial Supercharging is natural supercharging that occurs at certain engine speeds, due to the inertia (momentum) of the air in the intake runners. The effect is tuned by careful design of intake plennum and runners, and is encouraged to occur over a broader range of engine speeds by variable-volume intake systems such as TVIS.
Turbo: Contraction for "Turbine Supercharger". See Supercharger.
TVIS: "Toyota Variable Intake System".
It's actually pretty simple. You know your engine is a 4-valve-per-cylinder design -- that's two intake valves and two exhaust valves. The purpose of two valves of each type is that each valve is half the weight of one big valve -- so this means that it can pop open and closed quicker. Two valves can open and close faster than one big valve, and this is usually the limiting factor in how fast the engine can go. Your redline is 7200 RPM, and it's that high mainly thanks to the 4 valves per cylinder instead of 2.
So, cam shafts actuate the valves, and they determine the lift, duration and timing of the valves' open-time and closed-time. The cams can be tuned either to give low-end torque OR high-end power, not both. To get both, it takes a variable-valve timing system like Honda's VTEC, or a variable volume intake system like TVIS.
Here's how TVIS works: at high-RPMs (above 4200 in the 3S-GTE), the engine works like TVIS wasn't there. You're in the sweet spot of the cams, and the engine makes piles of power. But if the engine worked the same way at low-RPMs, then you'd have no torque and a rough idle. In other words you'd be "off the cams". So what TVIS does is it closes off one intake runner to each cylinder -- that's one of two, since each intake valve gets its own runner (the runner carries air from the main intake chamber down to the valve). So really each cylinder is running off only one intake valve, at low RPMs. This might seem counter-productive, but really at low RPMs the engine can get enough air through only one valve. The consequence of this is that the air in the one runner has to move twice as fast to fill the cylinder - in other words, that moving air has twice the momentum. This is the point. As the piston starts moving up again after the intake stroke to begin the compression stroke, that intake valve is still open. Why doesn't some air get pushed out again? Because of the momentum of the air in the runner still trying to push more air in. This is called Inertial Supercharging.
The result of having TVIS is to broaden the torque curve, and it is why the MR2 makes tonnes of power from 3000 RPM right up to and beyond 6000 (see dyno chart of stock MR2 Turbo). TVIS the system itself is simply eight little butterfly valves, one over every other intake runner, that are open above 4200 RPM and closed below.
WOT: Wide Open Throttle.
