Turbo Charged - Import Tuner Magazine

In our first installment of Horsepower 101, we learned about the basics of nitrous oxide. For our second installment, we will look at two other power adders that rely on the magic of boost pressure--turbos and superchargers.

How it WorksMash the pedal and feel the power come on as the boost gauge climbs. In most instances, as the boost pressure climbs, so does the power.

But what is boost pressure and how does it help to make more power? Both a turbo and a supercharger fall under the classification of a "forced-induction" device. As such, both devices try to force additional air into the engine. Boost pressure results when the turbocharger or supercharger's compressor feeds more air into the engine than it would normally ingest. As a result, an abundance of additional air begins to build pressure inside the intake manifold. This supply of air, at a "boosted" pressure above the natural norm, fills the cylinders with a higher mass of air once the intake valves open.

More Boost = More Power?In simplified terms, more boost pressure usually results in more power. Of course, there are always exceptions. These exceptions result either due to misapplication or going beyond the intended use of the turbocharger or supercharger system. In these cases, the advantage of the higher boost pressure is offset by a larger disadvantage of a charge temperature increase. To avoid this pitfall, it is important to select the turbocharger or supercharger system based on the intended horsepower goals that you have set for your combination.

Burn More Fuel, Make More PowerAs we learned before, the more fuel that you can combust, the more power that you can make. Combusting fuel requires oxygen. In the first installment of Horsepower 101, we learned that nitrous oxide supplies an abundance of oxygen to the mix. Having an ample supply of forced additional air (which would contain a higher mass of oxygen, too) allows us to combust more fuel.

Regardless of what type of forced-induction is being used, every turbocharger or supercharger system accomplishes both of the above. In some way, either through the factory injectors or by upgrading to larger injectors controlled by some type of engine management, the turbocharger or supercharger system puts more fuel into the engine. The additional amount of oxygen needed to burn this fuel is also supplied by the forced induction system.

The Basic Systems (Positive Displacement, Centrifugal, Turbo)All forced-induction systems designed for automotive use fall under three categories; positive-displacement supercharger, centrifugal supercharger and turbocharger. Each of the three systems has some shared and some unique characteristics.

Positive displacement superchargers are pulley-driven by the engine's crankshaft, use the size of the pulley to determine boost pressure, have a low-to-medium-high compressor efficiency, provide peak boost instantly. Examples would include a Jackson Racing supercharger or the factory supercharger in the first-generation, supercharged MR2.

Centrifugal superchargers are also driven by a pulley-driven by the engine's crankshaft and also use the size of the pulleys to determine peak boost pressure. A centrifugal supercharger has very high compressor efficiency and can be teamed to an intercooler system easily. The boost curve of a centrifugal supercharger is very different from a positive-displacement supercharger. A centrifugal supercharger builds boost proportional to rpm. If peak boost is configured to 8 psi on an 8000 rpm redline engine, the system will produce 4 psi of boost pressure at 4000 rpm, 6 psi at 6000 rpm and 8 psi at 8000 rpm. While this boost curve would sacrifice some low-rpm performance, it can also act as a built-in traction control for front-wheel-drive and street tire vehicles. Examples of centrifugal superchargers would include Vortech and ProCharger.

Turbochargers are essentially turbine-driven superchargers. Unlike a supercharger that uses the crankshaft to power the compressor, a turbocharger uses the enthalpy of the exhaust gases to power the compressor. What the heck is enthalpy? Enthalpy is basically the amount of energy contained in both the heat and velocity of the exhaust gases. Exhaust gases can be 1,400 to 1,800F. The turbine section of the turbocharger converts the enthalpy into shaft power to spin the compressor section.

The sizing of the turbine housing, turbine wheel, compressor housing and compressor wheel all affect the boost response characteristics of the turbocharger systems. In general, a turbocharger's boost response falls somewhere between a positive-displacement supercharger and a centrifugal supercharger. The efficiency of the compressor is generally very high unless the turbocharger is mismatched for the application. Turbocharger systems are available from APEX Integration, HKS, GReddy, DRAG, FMAX, Rev-Hard and XS Engineering to name a few. Intercooler systems are easily added and can be a big benefit on all gasoline-burning applications.

The Good, The Bad, The UglyThe good news is that forced induction offers the biggest full-time power improvements. Unlike nitrous-oxide systems, there is no bottle., so the performance increase never runs out. For full racing applications, nothing can touch the power potential of a turbocharged engine. The horsepower increase from a properly installed supercharger or turbocharger system is typically on the order of a 40- to 80-percent increase. Most basic systems come ready to generate additional horsepower extremely reliably, as long as the engine is in good mechanical condition and the system is installed properly.

The bad news is that an improperly installed supercharger or turbocharger system can cause severe engine damage. With turbocharger systems the urge to crank up the boost beyond recommended levels is a real danger. When engines are asked to produce more power than they can handle then parts break. Connecting rods and pistons are usually the first parts to let loose. When forced induction puts the air into the engine without enough fuel added or no fuel at all, then you've got trouble. The temperatures in the combustion chamber will skyrocket. The engine may detonate and parts will be broken and melted.

There are some ugly facts that you'll have to face when it comes to using a supercharger or turbocharger system. First, boost and horsepower are extremely addicting. The more you get, the more you want. Second, the less you learn about forced induction, the more likely you are to have a bad experience. Third, every engine has its limit. A stock engine doesn't have the toughness of a racing engine. Chances are that there's a tuner out there with your same engine and supercharger or turbocharger system. Use their experiences to your advantage.

Better Safe Than SorryIf you want to have a good forced-induction system experience there are some considerations you can make to increase the chances of coming away with a smile. Since a turbo or supercharger system relies on the fuel system, it is always best to be sure that your fuel system is at its peak efficiency. Factory fuel filters begin to degrade in performance as early as 10,000 miles. When installing a new forced-induction system, it is recommended that you replace your factory fuel filter and be sure that the injectors are clean.

The other area that you need to address is the vehicle's ignition system. A factory ignition system is designed to operate at near factory horsepower levels. A forced-induction system can easily overcome the capabilities of a stock ignition system. Be sure that the spark plugs are new and that the ignition cables are in good condition. The cap and rotor should also be inspected on non-direct-ignition-system (non-DIS) cars. To ensure a good spark, an ignition amplifier, high-performance ignition wires and spark plugs that are one heat range cooler (for applications over 50 hp) are highly recommended. In the absence of an ignition amplifier, it's a good idea to tighten your spark plug gap by .010 to .005 in.. This will make it easier for your ignition to generate a spark even in the high-horsepower.

Finally, for forced-induction applications, especially turbocharger applications, a larger-diameter free flowing exhaust system is a must. On turbocharged applications, larger exhaust systems will actually improve boost response as well.

Coming SoonIn the next installment of Horsepower 101, we'll take a look at camshafts. That's right, the magic of bumpsticks will be revealed. Knowledge is power; we'll catch you next month.