Blow-Off Valve: A spring loaded diverter valve placed in the inlet path of the engine that lets boost pressure from the supercharger to blow-off before getting to the engine when the driver is not accelerating hard.  The valve is operated by a vacuum created beyond the throttle plate (i.e. in the intake manifold).

Boost: Pressurizing an internal combustion engine's intake, with a supercharger, so that it processes more air and fuel than it would when naturally aspirated, (letting mother nature fill the cylinders).  Boost is measured in pounds per square inch.  Normal atmospheric pressure, at sea level, is 14.7 pounds per square inch.  If you run 14.7 pounds of boost you will effectively double the effective displacement of your engine.  A 463 cubic inch engine becomes almost as powerful as a 926 cubic inch engine without a significant increase in weight. 

Detonation: The pinging noise produced when valves are slammed shut by the ignition occurring to soon rather than being allowed to close by their own spring tension.  It is usually associated with low octane fuel, a lean mixture, or the ignition timing being too advanced.  See Stoichiometric.

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.

Fuel Cut:  An action taken by the ECU, in self defense. In response to a signal from the speed sensor indicating that the vehicle has exceeded maximum speed, the ECU immediately stops all fuel delivery at speeds above 99 mph.  The triggering of Fuel Cut is a very traumatic experience for both car and driver.  Remedying this problem with Fuel Cut is apparently as simple as wiring the electric fuel pump power through the ignition switch rather than from the ECU.

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 unburned 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.

Intercooler: When air is compressed, the temperature rises and the density goes down. Reduced air density would not lead to improvement of combustion efficiency. An intercooler cools down the air compressed and heated by the turbocharger thus eliminating the loss of density.  A typical intercooler reduces your boost pressure by around two and one half pounds.  This project will avoid that loss by mounting the turbochargers at the rear and the pipe returning air to the intake will serve as an intercooler since it is exposed to air-flow on the underside of the truck.  This will produce only about a half pound of boost loss.

Porting: A high speed grinder and several grinding stones are used to meticulously and methodically increase the size of intake and exhaust ports to their original engineering specifications.   This makes it easier for air and fuel to flow through the engine, thus, it becomes more efficient.  The process of removing the casting flaws from heads and leaving their runners with a machined surface rather than a porous one that causes turbulence by it's sand cast surface.   The combustion chamber is also machined and any sharp points are removed.

Stoichiometric: (stoik-e-o-metrik) 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 Stoichiometric is considered a "rich" mixture; less fuel makes the mixture "lean."  A rich mixture burns cool and leaves carbon monoxide and unburned hydrocarbons in the exhaust gases. A lean mixture burns hot and fast, and therefore leaves more unused oxides of nitrogen in the exhaust.

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.  Most other superchargers are run by a belt off the engine. Other uncommon drive mechanisms include hydraulic and electric.  While they perform the same function, turbochargers and superchargers go about it in completely different ways. As has already been mentioned, a turbo is driven by the exhaust gasses which are already being expelled from the engine. So, in effect, turbos add 'free' power since their compression is created by what was already discarded.

Superchargers, however, are different: they are belt-driven. They feature a pulley whose belt is directly attached to the crankshaft, this allowing them to spin in direct proportion to the engine itself. The upside is a near absence of lag (see below); at least some boost is typically available the instant you crack the throttle. The primary drawback to a supercharger, however, is that they take power to make power. The overall result is more power than there would be without the supercharger; it's just that they aren't as efficient as a turbocharger from an energy standpoint. Other drawbacks include lower mid-range power than a turbo, lower thermal efficiency than a turbo, (sometimes) much harder to incorporate intercooling, etc.

Throttle Position Sensor (TPS): A potentiometer (like volume control) that sends an increasing voltage to the engine control unit, ECU, so that it knows how hard the driver is pressing on the accelerator pedal.

Turbo: Turbocharger - Contraction for "Turbine Supercharger."  Quite simply, a turbo is merely an exhaust-driven compressor. Imagine a small shaft about the size and length of a new pencil. Now rigidly attach a pinwheel to each end of the pencil. One pinwheel (called the turbine) is placed in the path of the exhaust gases which are exiting the engine. These gasses are 'caught' in the turbine, causing it to spin. This in turn spins the whole shaft, along with the pinwheel on the other end (called the compressor). The compressor is placed in the intake air's path; once it begins spinning, it actually compresses the air on its way into the engine.

Why is this hot? Well, normally aspirated engines have to work to draw in their intake air. In other words, as the intake valves open, the piston's downward movement creates a vacuum which 'draws in' some air through the intake system. Ideally, the piston's movement would intake 100% of the air that could fill the combustion chamber. In the real world this is not the case; the typical engine will draw in only about 80% of the total volume of the combustion chamber. There are many causes for this--intake restrictions, valve timing, camshaft design, and much more.  Now imagine that the engine mentioned above has a turbocharger. When the turbo compresses the air it builds up pressure in the intake manifold.  So now when the intake valves open, air is actually forced or blown into the combustion chamber. (This is one reason why turbocharged engines are sometimes referred to as 'blown' or 'forced-induction' engines.) As you might imagine, this allows for more air to fill the chamber; the amount can be far greater than 100% of the chamber's actual  volume, thus the tremendous gains in total available power. 

Okay, so now we have more air entering the engine. To benefit from this, we need more fuel to match. On computerized cars, various sensors will see this amount of boost pressure and increase the amount of fuel accordingly. Now that we have more fuel entering the engine, more power is made. (Yes, when you get right down to it, the only way to make more power--on any engine--is to burn more fuel.)  Our 454 cubic inch engine can perform as if it were a 908 cubic inch engine just by boosting 14.7 pounds.  More boost is possible if the engine has been built to handle the increased power.  Obviously it isn't the goal of this project to produce the most fuel efficient Hummer in the world, we'll settle for one of the fastest and just add a larger fuel tank so we can make it to the next filling station.

Turbo Lag: The majority of turbochargers feature a waste gate which allows some of the exhaust gas to be directed around the turbine. This allows the turbo's shaft to spin at a reduced speed, promoting increased turbo life (among other things). Think of it as a 'stand by' mode. Since the turbo isn't needed during relaxed driving anyway, this effect is harmless...

...until you suddenly want to accelerate. Let's say that you are loafing along, engine spinning 1500 rpm or so. You instantly floor the throttle. The exhaust gas flows through the turbo and cause it to spool (spin up to speed and create boost). However, at this engine speed there isn't very much exhaust gas coming out. Worse still, the turbo needs to really get spinning to create a lot of boost. (Some turbos will spin at 150,000 rpm and beyond!) So you, the driver, need to wait for engine revs to raise and create enough exhaust gas flow to spool the turbo. This wait time--the period between hitting the throttle at low engine speed and the creation of appreciable boost--is properly called boost response. Many people incorrectly call it lag, which is really something different. Lag actually refers to how long it takes to spool the turbo when you're already at a sufficient engine speed to create boost. For example, let's say your engine can make 12 PSI at 4000 RPM. You're cruising along at a steady road speed, engine spinning 4000 RPM, and now you floor it. How long it takes to achieve your usual 12 PSI is your turbo's lag time. Between the two, slow boost response usually causes the most complaints.

There are two aspects to consider when dealing with boost response: engine factors and driver factors. As far as engine factors go, there are many things which affect turbo lag... although most are directly related to the design of the turbo itself. Turbos can be designed to minimize lag but this usually comes at the expense of top-end flow. In other words, you can barter for instant boost response by giving up gobs of horsepower in the upper third of your RPM range. (Behold the catch-22 in designing one turbo for all uses.)

Driver factors are another matter. You basically need to understand how a turbo works and modify your driving style accordingly. To sum it up, don't get caught with your pants down! If you feel that there may soon be a sudden need for serious thrust, downshift until your engine speed is at least 3000 RPM. This way there will be noticeable boost almost as soon as you hit WOT. If you are going up a hill at WOT around, say 1800 RPM and your speed is dropping, you'll need to downshift just like any other car in the same situation. Remember: turbos need exhaust gas in order to spin. Let them have some when they need it.

Waste Gate: A valve, operated by boost pressure, that discharges exhaust gasses before they enter the turbocharger and cause too much boost.  Most are spring operated and many feature an adjustment so that the operator can adjust the desired amount of boost with a screwdriver or Allen wrench.

WOT: Wide Open Throttle.