Technical Articles

Webster’s Dictionary defines su-per-charg-er, “A device by which an increased quantity of air is supplied to the cylinders of an internal combustion engine, producing greater power.”

So, is a turbocharger a supercharger?

Well, yes by definition. Common in today’s language is the term “forced induction systems.” Both superchargers and turbochargers are forced induction systems.

Confused yet?

Hopefully this article will sort out some of the confusion.

Both superchargers and turbochargers compress the air flowing into the engine. By compressing more air into each cylinder, more fuel can be added in the process. More air and fuel per stroke means more engine power. Simply stated, turbo/supercharged engines produces more power overall than the same engine without the charging.

The amount of air added to a supercharged engine is measured in terms of boost. Normal atmospheric pressure is 14.7 pounds per square inch (psi) at sea level. A naturally aspirated engine, like in a stock Hummer, therefore has 14.7 psi of air entering each cylinder during the power cycle when driven at sea level. The typical boost provided by either a turbocharger or a supercharger, in street applications, is 6 to 8 psi. At 7.35 pounds of boost, you are getting about 50-percent more air into the engine. Therefore, with the proper amount of fuel added, you would expect to get 50-percent more power. All superchargers have some losses and are not perfectly efficient, so in the real world you might get a 30-percent to 40-percent increase in power at 7.35 pounds of boost.

Supercharger types

There are four major types of forced induction systems used in the marketplace today.

The roots supercharger, the twin-screw supercharger, the centrifugal supercharger and the turbocharger.

Type in these words in “google” and you will get enough charts, graphs, data, misinformation and opinions to confuse a seasoned mechanic. Keep the following in mind. Each of these superchargers has advantages and disadvantages. No one can say with 100% authority that their supercharging system is best. This article briefly explains these different systems so that you can choose a supercharging system that is right for the way you drive your Hummer

Roots Type Superchargers

The oldest and best know supercharger is the roots supercharger. Its basic design dates back to the 1880’s when the Roots brothers designed it as an air conveyor for mine shafts.

The roots blower is a positive displacement unit. Every revolution of the blower produces a fixed volume of air. The result of this fixed volume of air is that boost is produced early as the engine RPM increases. Most roots superchargers produce full boost at 2000-2500 RPM.

Eaton improved upon the roots blower by taking each rotor and twisting them 60 degrees to form a helix. The two counter rotating rotors have three intermeshed lobes that help reduce pressure variations and provide a smooth discharge of air.

Magnuson Products has the most popular roots type supercharger systems on the market today and uses the newer style Eaton blower. Their system also includes a small bypass valve placed between the throttle body and the supercharger that practically eliminates any power drain associated with the supercharger under normal cruising conditions when no boost is needed.

Magnuson Roots Type Supercharger

Twin Screw Supercharger

Mr. Alf Lysholm originally invented the twin-screw supercharger in the 1930’s.

Many people confuse the twin-screw supercharger because they look similar to a roots supercharger, especially inside an engine compartment. However, they differ in that as a twin-screw supercharger draws air, the design of the rotors actually compresses air before discharging it from the supercharger. Because the compressing of air is done inside the supercharger, the twin-screw supercharger produces less heat than a roots supercharger. Just like the roots blower, the twin-screw supercharger produces a fixed amount of air with each revolution and reaches full boost early in the RPM band, with full boost in the 2000-2500 RPM range.

Kenne Bell Twin Screw Supercharger

Centrifugal Superchargers

Centrifugal superchargers are based on technology that is newer than the roots or twin- screw superchargers. What differs is that the centrifugal supercharger is NOT a positive displacement supercharger like the roots or twin screw. A centrifugal supercharger spins an impeller at high RPM, accelerating air after it enters the unit. Centrifugal force moves the air to the outside of the spinning impeller blades. Before exiting the unit, air is forced through a diffuser, which slows down the air, creating pressure. This air is then piped to the engine intake.

One significant difference between a centrifugal supercharger and a roots blower is that the centrifugal is a true compressor rather than an air mover. This means that the air exiting the centrifugal is already under pressure.

Centrifugal superchargers build boost relative to engine RPM. These superchargers start boosting around 2000 to 3000 RPM, and attain full boost at max RPM. Boost builds exponentially in the upper half of the power-band. The quoted maximum boost of a centrifugal supercharger occurs at max RPM for the engine and at a lower discharge temperature than a roots blower.

Vortech Centrifugal Supercharger

Turbochargers

The key difference between a turbocharger and a supercharger is its power supply. All three superchargers described thus far are belt driven. This means that it takes engine power to produce supercharger power.

With a turbocharger, exhaust gases from the engine are used to spin a turbine. This turbine is connected to a compressor similar in design to the centrifugal supercharger described above. Air discharged from the compressor is piped to the intake manifold to make boost.

The design of a turbocharger is critical because inherent in all turbochargers is turbo lag. It takes a second or so for the turbine to spin up and create boost from the compressor. Smaller turbochargers as are found on most street engine applications will provide boost more quickly and at lower engine speeds because smaller units quickly overcome the inertia of the turbocharger’s rotating parts. However, at higher turbine speeds as the throttle is increased, too much boost may result. A wastegate is used to reduce boost at higher RPM. If the pressure gets too high the wastegate bypasses some of the exhaust around the turbine blades, allowing the blades to slow down.

Most turbochargers are mounted in the engine compartment with the exhaust gases being supplied from one of the exhaust manifolds. For the Hummer H2, Squires Turbo Systems has developed a turbo charging system that mounts the turbine and compressor near the end of the tail-pipe.

STS Remote Mounted Turbo System (shown on an H2)

Supercharger Design Considerations

When manufacturers are designing their units, they look at a number of factors inherent with forced induction systems.

Volumetric Efficiency:

To keep things simple, it is a measure of the CFM of air in vs. the CFM of air out. When volumetric efficiency drops off due to leakage or design, so does boost and therefore power. Boost will not drop off as engine RPM increases on a supercharger with a high volumetric efficiency.

Adiabatic Efficiency

Basically this is a measure of how much engine power it takes to run the supercharger. The more power consumed to run the supercharger, the less overall power available to put to the wheels. All belt driven superchargers have some parasitic loss because they are belt driven which is part, but not all, of the equation for adiabatic efficiency.

Turbochargers, are driven by exhaust gases and therefore do not use any of the crankshaft's power in order to operate. A turbocharger does increase backpressure in the exhaust upon start up so some engine power is also used to run the turbine and compressor. This is loss is minimal and equals out with the increased inlet pressure for the majority of the powerband. Turbochargers have the least parasitic loses of all forced induction systems.

Temperature Efficiency

This is simply the temperature of the air measured before it enters the supercharger as compared to the temperature of the air after it exits the supercharger. Superchargers with higher exit temperatures are obviously less thermally efficient.

High temperatures are what damages most engines with superchargers installed. When air is compressed, increased heat is an inevitable result. Excessive heat can lead to detonation or “knock.”

Engine timing dictates when the spark plug ignites to make the best use of the air fuel mixture entering the combustion chamber. Under normal conditions, the spark ignites the mixture just before the piston reaches the top of the compression stroke. The flame front moves the spark towards the outside of the cylinder in a controlled fashion and a smooth burn is the result.

Detonation or “knock” occurs when the air fuel mixture that is ahead of the flame front ignites early, before the framed front arrives. This is due to the air fuel mixture being overheated. Hotter air entering the combustion chamber due to supercharging along with the heat of the compression stroke causes this overheating. When this air fuel mixture ignites early, the controlled burn becomes uncontrolled and will cause a pinging sound or “knock”. Prolonged detonation (even a few seconds of knock) can lead to engine damage. Cylinder head damage is the common result but detonation can also damage piston rings, pistons, bearings, and rods.

The most severe type of detonation is pre-ignition. This occurs when the air fuel mixture is so hot that it ignites the air and fuel mixture during the compression stroke before the spark plug even fires. The piston travels up into a wave of exploding gas. This condition can easily bend connecting rods, ruin rings, and crack pistons.

Intercoolers

To reduce the heat caused by the compressing of air, many manufactures offer intercoolers with their (technically an aftercooler since they cool air after it is discharged from the supercharger and before it enters the intake manifold.) kits. An intercooler looks like a radiator and takes away heat through an air to water exchange. There are some air-to-air intercoolers but they are not used in Hummer kits.

Some experts state that cooler supercharged air entering the engine makes more power. This statement is a little misleading. Cooler air entering the engine by use of an intercooler DOES mean that there is less chance of detonation, which can lead to a longer power cycle and therefore more overall power.

Volumetric, adiabatic, and temperature efficiency are mentioned here because arguments occur constantly regarding which supercharger is best based on these factors. What counts is how these factors are overcome to produce more” power under the curve.” Arguing these factors as the sole basis for choosing a particular supercharger is irrelevant. The overall power produced and at what RPM that power is produced is what counts.

For example, Top fuel dragsters roots blowers, which have the greatest parasitic losses of all designs. Due to parasitic losses, it takes 900 horsepower to run the blower. However that same engine in producing thousands of horsepower and the top fuel dragster runs the quarter mile in under four seconds!

Other Considerations:

Most superchargers available for the Hummer H2 already have the following but it is important to mention these considerations:

ECU Programmer:

Make sure your kit comes with a programmer that reprograms your ECU for the supercharger being installed. Manufacturers spend thousands of hours making sure that critical engine parameters are set up for the newly installed supercharger. Some kits used to offer a piggyback controller that was added to the ECU. In today’s electronic world it is almost impossible to get a piggyback controller to communicate properly with the ECU. A properly programmed stand-alone programmer that recalibrates the vehicle installed ECU is the way to go.

Quality & Reliability:

The longer a manufacturer has had systems on the market, the “bugs” associated with the system are most likely been solved. Also issues related to quality have been corrected. This is similar to a new model year vehicle. The 2004 and 2005 H2s have had minor improvements based on the 2003 feedback. If you are buying the “newest” supercharger on the market, make sure the company has had similar experience with comparable supercharger systems.

Make sure numerous hours of testing have been performed both with a dynamometer and also on the road. You do not want you H2 to be a test platform for the manufacturer unless this agreed upon up front.

Complete Kit:

Make sure the kit comes with everything you need for a complete installation. This includes properly sized fuel injectors, additional fuel systems (if required), and all necessary hoses, clamps, etc. All kits send the major components; make sure they send the minor ones as well. Also ensure that complete instructions, including ECU programming instructions are part of the package.

Warranty:

This is one of the most misunderstood areas regarding superchargers. Most kits come with a warranty. Their warranty is for the supercharger kit they are selling you. It is not for your powertrain-period.

Some manufacturers offer a second warranty for you engine and drive train at a price of $200.00 or so. This warranty typically offers $3000.00 for the engine and $2000.00 for the drivetrain in the event they are damaged due to the increased horsepower and torque created by the supercharger installation. If you read the fine print of this warranty, it will state that all other engine components must remain factory for the warranty to be valid since the supercharger was designed for a factory engine.

Many Hummer owners are driving around with a supercharger and also with headers, cat back exhaust and an aftermarket air filter. They think their add on warranty for the engine and drive train is in full effect. It is not.

It is possible for you to buy a warranty that also includes other modifications as well as supercharger damage. However, the modifications must be disclosed to the warranty company and it will most likely be too expensive to buy.

The MAGNUSON MOSS WARRANTY ACT, US Code - Title 15, Chapter 50, Sections 2301-2312 states that legally, a vehicle manufacturer cannot void the warranty on a vehicle due to an aftermarket part unless they can prove that the aftermarket part caused or contributed to the failure in the vehicle. Some owners think that this means of their engine or drivetrain are covered under this act after a supercharger is installed. Chances are almost 100% that GM will consider the supercharger the cause of the engine or drivetrain damage.

The ACT, in principle, protects the Hummer owner from their entire warranty being voided because of a supercharger installation. For example, under this ACT, the dealer or GM cannot refuse to fix your mirror or other items covered under warranty simply because you installed a supercharger. They can however void your engine and powertrain warranty.

When you think about it, this makes sense. You can’t expect GM to provide an engine and powertrain warranty after you install a device that can provide up to 50% more power.

If you have questions regarding exactly what is and is not covered after a supercharger installation consult your dealer or a GM representative, not the supercharger manufacturer.

Advantages & Disadvantages

Keeping the above factors related to supercharger performance and design in mind, which supercharger is right for your Hummer H2? As stated at the beginning of this article, it depends.

Each manufacturer will argue that their system is the right system. Each has its advantages and disadvantages.

An advantage of the roots and twin-screw superchargers is that they inherently provide instant boost. So, if you are at a stoplight and want to move away quickly, these are the superchargers of choice. They will give you that “push you back in the seat” feeling because the response is very quick. Also, while on the highway, the rapid response of these units makes passing seem effortless.

A disadvantage of the roots supercharger is that it creates a lot of heat when at full boost. After 10-12 seconds, discharge heat causes the timing to retard in order to prevent detonation, which then results in a power drop. The also happens with the twin-screw but to a lesser extent since discharge temperatures are lower. On the street, if you are at full boost for 10 seconds or more, you will surely get a speeding ticket!

The centrifugal supercharger has the advantage of fewer moving parts and is very reliable. It does not make boost until 2500-3000 RPM so a lag in power is felt early on. Also the boost curve is almost linear with max boost occurring at red line RPM. This is viewed as a disadvantage to some daily drivers since the boost potential is not normally realized in street conditions. In racing applications, more boost can be obtained at the high end than either the roots to the twin screw and the high end of the power band is where the racer uses the engine.

The advantages of a turbocharger are less parasitic losses, cooler discharge temperatures, and due the wastegate, constant boost can be maintained after the turbocharger spools up around 2500-3000 RPM. This means a high boost level or max boost can be obtained during daily driving conditions. The turbocharger has more moving parts than the others and some view this as a disadvantage since more parts mean more potential problems. Also, a turbocharger does not make boost until 2500-3000 due to turbo lag.

More Power?

Many Hummer owners love the power their properly installed and tuned supercharger provides. Some begin to wonder, “if six pounds of boost make it run this good, then lets try to get eight or ten pounds of boost!”

This can be easily done on all the superchargers mentioned here. A common example is installing a smaller pulley on a roots blower. The supercharger will force more air in per engine revolution and more boost can be made. Other methods achieve are used to make more boost on the other types of superchargers mentioned here.

Keep this in mind. MORE BOOST DOES NOT ALWAYS EQUAL MORE power. The Hummer H2 units are designed for a certain boost level. Increasing that boost level could lead to high discharge temperatures and a reduction in timing. Also the system could fail to provide enough fuel for an increased boost level, which in turn leads to a leaner engine, and more heat production.

Changing boost levels from the manufacturer’s design boost levels should be done with caution. A dynamometer should be used along with tuning software to make sure the increased boost level is performing as intended. Also keep in mind that a stock engine can only take so much increased stress. In many cases, higher boost levels require better pistons, crankshafts, and connecting rods to ensure the engine can withstand the higher boost levels.

Conclusion:

Note: The above table is for comparison purposes. All Hummer H2 units make six to eight pounds of boost for street applications.

For a Hummer H2, all of the superchargers discussed here can have an application. Too many times, arguments regarding parasitic loses, volumetric efficiency, max boost, normal boost levels, etc. cloud the issue facing the H2 driver.

Useable, reliable power in street and off road conditions should dictate which system you install. Some owners prefer the instant boost provided by the roots and twin-screw superchargers. Others will trade that instant boost for turbocharger or centrifugal supercharger based on their use of the H2.

Hummers Gone Wild hummersgonewild.com supplies and installs all types of forced induction systems for the Hummer H2.as well as for racing applications. Feel free to give them a call at 609-689-0714 or e-mail them a question at info@hummersgonewild.com.