BrandonSB

which is more efficient? a supercharger or a turbo? whats the difference?

bitchin_buick

How much money do you have? Really?

BrandonSB

enough just a question i think can help anybody looking to add some power to there vehicle.

bitchin_buick

Point taken! What 3rd do you have? Profile shows nothing........

TheMonster

What engine, what trans?

BrandonSB

87 z28 ill have to update some!

BrandonSB

454, TH350,

just wondering the difference between them both, i think everyone would benefit from knowing the difference to help make there decision.

lb9 GTA

I'll start with whats different. All superchargers are driven directly by the engine either by a belt, gears, or on really old setups bolted to the crankshaft itself. The typical supercharger that bolts on top of the engine is a roots/screw type. It uses two rotors that mesh together and pull air into the engine. The other type of supercharger is the centrifugal type. It looks sorta like a turbo. The air is pulled into the inlet and flung into the "compressor housing" (the snail looking thing). As more air is flung into the compressor housing it is forced through the spiraling passage that gets prograssively slightly smaller compressing the air and then pushed out the outlet and into the intake track of the engine. Turbochargers are similar to the centrifugal type supercharger but is driven by the energy in the exhaust gasses that spin an impeller which then spinns the compressor via a shaft.

Another difference is that superchargers tend to effect the power band of the engine quite a bit where as once a turbo is spooled, it tends to follow
the power band of the engine.

As for what is more efficiant. Because turbochargers are not driven directly by the engine but essentialy waste energy unlike superchargers, turbochargers are more efficiant.

I hope that explains it clearly enough for you.

If anyone is better educated on the subject feel free to correct me

BadBowtie87

lb9 pretty much hit the nail on the head. Efficiency is best served via turbo. Superchargers "take power to make power" because they are belt or gear driven.

BrandonSB

i heard turbos tend to lag aswell? via google.. hold on ill paste it..

http://www.automotivearticles.com/12...charger_.shtml

Brian Ferrari Explains..

lb9 GTA

That depends on the sizing of the turbo as well as the system design its self. The lager the turbo the longer it takes to spool up. There are ways to move the same amount of air and get less lag tho. Two smaller turbos will spool faster than one large one. Automakers often go that route when dealing with more than four cylinders. They sometimes to go one step further and use whats called a sequential twin turbo system. Instead of using two equal sized turbos they use one small turbo and one larger turbo. That allows boost to come in earlyer and smoother. The exhaust manifolds also play a roll in how the turbos spool. Tube headers will start to build boost faster than log style manifolds due to increased exhaust flow.

IMO a little lag = launch control

BrandonSB

good point

vwdave

I think I can write a book on this topic as Ive ran both. A procharger P1SC in a harley F150, and misc turbo setups. Im just going to make a few points. Notice Im going to be talking about procharger type blowers.

Two terms we have to get straight. Boost threshold, and lag. Boost threshold is the amount of time it takes for the motor to get the turbo spinning at low rpm's. Lag is the amount of time it takes to get into the power when the engine is above boost threshold. Think about holding the car at 3500 rpms and punching it. The time it takes for it to respond is lag.

Regardless of what others tell you, there is no wrong way. Just different ways. The Procharger took on the powerband of the motor with the same curve. Just drastically higher. It took some RPM for it to really start moving. It still has to fill up the intake piping with pressure and airflow before it can start making power. So it did have "lag."

I have setup numberous turbos on many applications. Properly setup, the lag is minimal. But its a series of tradeoffs. Want a ton of top end? Youre going to have to have a big turbo which is going to have a poor response, but its going to scream. You want instant response and tons of mid-range torque, you have to give up some top end to do it. A smaller exhaust housing, smaller exhaust and intake pipes and such is going to contribute. The shorter and smaller those pipes are, the less lag you will have as it will have less room to have to fill before filling the motor.

The whole notion of "Wasted energy" and "free horsepower" is a load of crap. Youre effectively clogging your exhaust up with the turbo. The only reason people cant give you an exact figure is that afaik, there is no plausible way of measuring the amount of added backpressure vs the loss of horsepower that the turbo takes away.

bitchin_buick

Got any pics of the beast yet? Z28 with a 454 Isn't enough for you? I'm just jealous............

BrandonSB

i never stated i had the engine, i was asking what would be better because i plan on this build

BrandonSB

never meant for this to be a "bragging" or "ego boosting thread" as you might see it, i just think its a question that most people can benefit from learning about and find out about making there decision, im sorry if you misunderstood..

lb9 GTA

I respectfully disagree. The exhaust energy that powers the turbo is really only used by the engine for scavenging and, while you are creating a "clog" in the exhaust, that restriction and it's affect is infanitly variable depending on exhaust gas volume, turbine speed, and waste gate operation. The amount of power it takes for the engine to work a turbo is minimal at best especially when you consider that a turbocharger is also an exhaust sound deadening device making it possible to eliminate mufflers in some cases (see STS turbo systems or the Dodge Neon SRT4 [which came from the factory with a straight pipe after the cat] for example).

bitchin_buick

I never thought that.... I just love hot rods and was hoping to see pics..... I was just giving you a hard time in my last post.....

ZZ3Astro

From what I've researched on this subject, it appears the turbo's presence on the exhaust side does not amount to much loading on the engine.

An average number to work with of boost pressure vs pre-turbo exhaust back pressure is 1:1. Some setups approach 2:1 (boost charge:exhaust backpressure) and inefficient systems can go in the opposite direction. It's also interesting to note that this ratio is not fixed in any given system. It varies with operating conditions such as current boost psi.

The heat of the combustion process expands the 'volume' of the inlet air to several times its original volume. The expansion comes mostly from increasing the inlet air's temperature from ambient to 1300-1600 degree F. I don't know the expansion amount but I've found a reference to four times the original volume. If you're a math wiz, run the numbers through "The Ideal Gas Law". But assuming it is 4 x ambient 14.7 psi = 58.8 psi, not accounting for any heat losses transferred through engine cooling system. In other words, based on a 4:1 number, sealing a cylinder full of ambient air and heating it to ~1500 deg F would create a pressure of ~58 psi in the cylinder.

Upon combustion, the cylinder pressure in a naturally aspirated engine can be 600 to 800 psi (over 800 psi for a high performance engine). As the piston retreats and thus cylinder volume expands, this pressure will drop before the exhaust valve opens, but it will still be at a significant pressure when the valve opens. So if you have a 9:1 compression ratio and peak cylinder pressure at TDC is 600 psi, at the bottom of the stroke you should see 600 / 9 = 66.6 psi. Pretty close to the 4 x ambient number above fwiw.

Now factor in say 14.7 psi of boost to the ambient 14.7. A 9:1 compression puts non-ignition cylinder pressure at 264.6 psi. Ignition of that yeilding an expansion volume 4:1 ratio produces 1058.4 psi. Using the other method, double the typical 600 psi to 1200 psi. Now go through the combustion stroke and bring the piston to the bottom of the bore for the 9:1 (de)compression ratio and it yields 117.6 or 133.3 psi respectively. side note: I'd like to verify these numbers somehow.. Considering a 30 over piston has over 12.75 square inches, that 1058 psi number comes out to a peak force of more than 13,489 pounds pushing down on the rod!!

So the backpressure produced is about 10% of total exhaust pressure, although many other factors play in, such as exhaust valves opening sooner than BDC, thermal factors and fluid dynamics/velocity of the gases through the manifolds/headers.

None of this really matter though. You put a turbo on a V8 and you have a winning combo regardless!

BrandonSB

im jelous of every vehicle you own.

BrandonSB

hahahaha understood! i love hot rods/track cars aswell, i hope to have a build like this someday! im only young still and have lots of time to make something out of this car hopefully one day ill be able to throw up some numbers haha

ZZ3Astro

Haha well I'll give you that the Iroc is a cool car to have. The Duramax on the other hand has been a lot of bad luck for me. It is a truly wonderful truck but seems to have a black cloud hovering over it.

7-2010 - smash and grab $1000 in damage, $500 contents lost

8-2010 - entire top half of oak tree falls on it $5000 in damage, 4 weeks

9-2010 - body shop totally screwed up - complete redo of entire job + total repaint 3 weeks

12-2010 - contaminated diesel, $7000 and counting, almost 6 weeks so far

1-2011 - still in shop, two of the eight new injectors are bad

Still want it? LOL

bitchin_buick

I have 2 great teenage boys whom I love (sniff,sniff), but I can't wait till they are on their own..... Then dad's time is on! Time to change the locks yet?

vwdave

I never stated how much. Just debunking the typical notion that its zero hp lost by adding it.

For a fun experiment, I might make a turbo bbc for a drag car in the future. Ill make the setup, run it without the turbos (not even on the car) dyno and track test it, then add the turbos on and see what happens.

Also for a fun experiment, drive a car with a seized turbo. Slower than two old people going at it.

lb9 GTA

Very true. I imagine it'd be the same as driving a car with a clogged cat.

lb9 GTA

There's actually an old HRM article where they compaired a GMC style supercharger, a centrifugal supercharger, and a turbo on the same engine at the same boost level on a dyno. I've been looking for it so I can link it to this thread. There's some intersting information on it mostly when it comes to the difference in powerbands between the 3. IIRC the centrifugal made the most peak hp and the turbo made the most torque and average hp. It's probably over 10 years old so I'm having difficult time trying to find it.

BadBowtie87

And it would be that same as losing a belt on the supercharger, both centrifugal and roots type.

BrandonSB

find it yet?

lb9 GTA

I couldn't find it on their site. I'll have to find that issue and look in their arcives. I'll start looking for it tomorow. Been a little bussy.

lb9 GTA

Unless it's a positive displacement on a miller cycle. Then it just won't run.

BrandonSB

sounds good, your also local to me aswell.

Tony89GTA

iTrader: (7)

I remember that one, think I have it to and might even be a post on it on this site to IIRC.

Edit found the post https://www.thirdgen.org/forums/powe...-turbo-vs.html

83 Crossfire TA

iTrader: (2)

The supercharger on a miller cycle engine is there just to make up efficiency for the extra cycle, it should run without it, just not well.

lb9 GTA

The biggest difference in a miller cycle engine is that the intake valve is held open significantly longer. Like half way into the compression stroke. Without the SC you essentially blow half the intake charge out the intake and have very little compression. Add to that the fact that the SC used on those engines are positive displacement there would be almost no air in the cylinders for it to run on. It might run, but I'm sceptical. They deffinatly don't start without that belt hooked up.

Street Lethal

iTrader: (16)

I have to disagree here, there are no trade-off's. First of all, we choose our turbo chargers for our particular application, not just the overall displacement of the engine. What moves the turbine is the amount of air we squeeze into the combustion chamber, and this of course is depicted by our cam specs and overall cfm, as well as the velocity of that cfm during vacuum, and larger turbo's are no exception. Not to mention, what many people overlook is the overlap factor, as the right amount of overlap (which superchargers hate, but turbo's love) will help the turbo spool, not to mention the load (gearing) behind it, the amount of stall during gear changes from a roll, and from a standstill, a trans brake. Lag is a forgone conclusion in the turbo world. However, if someone were to throw too big of a turbo for their particular application because they simply don't understand the nature of symmetry, then I would completely agree with what your saying....

flrtin1

Here is a older dyno graph for a small roots vs centrifical in a controlled head to head comparison

"Here is a nice illustration which shows the typical Boost, HP, TQ responses from two different types of superchargers. This is a comparison between the Magnacharger (Roots type blower) and a ProCharger (centrifugal type blower). These dynos were performed on an SuperFlow engine dyno, using the exact same engine combos and tuning.

ProCharger D1 @ 10 psi boost intercooled
Magnacharger MP112 @ 10 psi boost intercooled
5.3L LSX based truck engine, with LPE cam and headers. Stock heads.
26 degrees timing, 103 octane fuel"

flrtin1

flrtin1

In this series we'll take a slightly more in depth look at the fundamentals of supercharging that were introduced in our "Supercharger Basics" article. This is part 1 of a 3-part series. After reading these three articles you should have a fairly strong understanding of what the supercharger does, what the advantages of each type of supercharger are, and how superchargers make so much damn power.
This article lays down the foundation of how superchargers came into being by taking a look at the fundamentals of creating more power, and looking back in history at where and how the technology originated.
Making More Power - Four Possibilities with One Common Thread
When it comes to extracting more power from an engine, the common goal, simply stated, is to burn more air and fuel per time. There are essentially four ways to achieve this end.
1.) The first way to make more power, is to make the engine more efficient by tuning the air and fuel delivery, reducing intake and exhaust restrictions, reducing rotating mass, enhancing spark energy, and tuning engine timing. This is the purpose of most aftermarket modifications, like air filters, ignition programmers, exhaust systems, etc. These modifications are very popular because they provide added power, they look good, and they sound good. Moreover, they can be done piece by piece, so your car can build with your budget. The problem with these kinds of modifications is that performance gains are small - often negligble and unnoticable. This is because most engines today are tuned fairly well from the factory, and are not equipped with highly restrictive intake or exhaust components, which would reduce fuel economy. In other words, if you're looking for more moderate power gains, you'll need to get to the heart of the engine where power is really made. Most of these modifications essentially have one goal in mind - make the engine more efficient so it can burn more air and fuel in a given amount of time.
2.) You can also make more power by speeding up the engine, i.e. spinning it at a higher RPM. This technique is very effective in producing more horsepower while keeping the engine lightweight and small. If you look at some of the fastest race cars in the world, you will find them spinning at incredibly high RPMs. The only drawback is that to spin at such high RPMs requires very high quality (and expensive) engine parts that can withstand the torture from the rapid rotation. Furthermore, the increased RPM substantially increases wear and tear on the engine resulting in decreased reliability and shorter engine life. Most street cars and trucks have a redline RPM of around 4000 to 7000 RPM. Spinning the engine faster than the redline RPM in street vehicles is risky without extensive engine modifications to support the higher rotational speeds. The goal with this option is also to burn more air and fuel per time.
3.) Another obvious way to make more power is to simply use a larger engine. Bigger engines burn more air and fuel, and hence, make more power per revolution. Of course, if it were that simple, we'd all be driving around with V-12s. You can fairly easily increase the size of the engine's displacement by boring the cylinders and running a larger piston, or by lengthing the stroke of the crank, but you can only go so far before you've bored the entire cylinder away or your piston is slamming into the cylinder head. To go really big requires a bigger engine, probably with more cylinders. The drawbacks of a bigger engine include their increased size (duh!?), increased weight, and reduced fuel efficiency. In addition, using a larger engine normally is not practical because it would require an entire engine replacement, which would be prohibitively expensive, and would require extensive modifications to mount it to the vehicle. Again, though, the goal of this technique is to (yep you guessed it) help the engine burn more air and fuel per time.
4.) The final way to make more power is to pack more air and fuel into the combustion chamber before igniting it. The end result is the same as using a larger engine. The problem with this technique is that it's not as simple as telling your engine to suck more air and fuel - it's restricted by atmospheric pressure. At sea level, atmospheric pressure is 14.7 psi, which is a measure of how densely packed our atmosphere is with air molecules. As elevation rises, air thins which, as you probably noticed on your last skiing / snowboarding trip, robs power from the engine. Now imagine if you could trick mother nature by making atmospheric pressure 21psi. You'd be packing around 50% more air, which means you could burn 50% more fuel, meaning you'd be making approximately 50% more power. You've probably already figured out that this is exactly what a supercharger does - it compresses air to pressures above atmospheric pressure (boost), thus packing more air into the engine. And you've probably also figured out that the goal of this technique is to burn more air and fuel per time. By utilizing this technique, a small engine can act like a big engine. It is more efficient because it has less weight and rotating mass. In addition, because you can control when the compressor (supercharger) is sending compressed air (boost) to the engine, and when it is not, you can enjoy stock fuel efficiency when the supercharger is not sending boost to the engine (normally at half throttle or less).

In reality there are more than four ways to make more power, but these are the four most conventional ways. You can also use a more potent fuel source that has more potential energy. This is the idea behind Nitrous Oxide and other high-energy fuels - a topic beyond the scope of this article.
A Brief History of the Supercharger
You may be wondering, "Who first thought of compressing air before sending it to the combusion chamber?" Don't run to the library just yet. We'll tell you!
It seems that just before the turn of the century (1900 that is), a German engineer named Gottlieb Daimler (yes, of Daimler Benz, Daimler Chrysler...) obtained a patent for a pump to aid in the delivery of increased amounts of air and fuel to the cylinder, and to aid in the removal of exhast gasses. He didn't call it a "supercharger" in his patent application, but that's what he was describing - this was the birth of the automotive supercharger. But in order to get to the true beginnings, we have to look evern further back in history.

Gottlieb's automotive supercharger design was modeled after a twin-rotor industrial "air-mover" invented and patented nearly 40 years earlier by Mr. Francis Roots (from Indiana) back in 1860. This technology is the foundation of the roots type "blowers" still used today! Soon after the roots air movers (they were not called "compressors because they did not compress air - they only moved it) were used in industrial applications, a German engineer named Krigar invented an air pump that itlizied twin rotating shafts that compressed. This technology would go on years later to become the foundation of the Lysholm twin-screw compressor used in today's automotive applications.


Apparently our old friend Gottlieb didn't have much luck in the early stages with his new invention, but the idea inspired French engineer Lois Renault, who patented his own type of supercharger soon after the turn of the century. It wasn't long before superchargers started to show up on American race cars. Lee Chadwick is credited with being one of the first American racers to successfully use a centrifugal supercharger in competitive racing, starting in the Vanderbilt Cup in Long Island, New York in 1908.Soon thereafter superchargers took to the air as World War I military engineers looked for new ways to make more powerful airplanes. Because airplanes fly at such high altitudes, the internal combustion engines that worked great on the ground, suffered at altitude in the thinner air. Although the technology wasn't successfully used in combat before the war ended, it was clear that sueprchargers were well on their way to becoming a mainstream power adding device.
Meanwhile, back in Germany, Mercedes was hard at work trying to make old Gottlieb's supercharger work. By 1921 they found success and released a glimpse of the first production supercharged vehicle utilizing a roots-type supercharger. Mercedes went on to manufacture several supercharged models with great success in the following years.
In the racing scene, supercharged cars were finding more and more success. By 1924, superchargers made their way to the Indy 500. Around the world, racers in Mercedes, Fiats, Bugattis, Alfa Romeos, Buicks, and MGs began using superchargers to help them to the victory circle. Mercedes found great success with their supercharged Grand Prix cars, while Harry Miller's supercharged Indy cars dominated at the Brickyard.
In the mid 1930's Robert Paxton McCulloch started McCulloch Engineering Company and began manufacturing superchargers as the first large American commercial supercharger manufacturer. They began developing superchargers for use on American passenger cars and hydroplane boats. This was the start of the supercharger industry in America as we know it today.Then came World War II in 1939, and the Allied forces had an ace up their sleeve in the form of the supercharged Spitfire fighter planes and B-29 SuperFortress bomber. These supercharged planes seemed almost unaffected by the altitude to the delight of Allied pilots and soldiers.After the war, superchargers took on a new life in the world of racing. Alfa Romeo and British Racing Motors used superchargers on their Grand Prix cars to the horror of the competition before they were eventually outlawed. At Indy, there was no such rule, and centrifugal superchargers howled their way to many vicories.

Paxton's first shop.

Paxton VS57 supercharger.That's it for part 1 of the series. Next time we'll take a look at the modern supercharger and the various technologies that make it work!

flrtin1

Welcome to part 2 of "Superchargers A-Z". If you haven't already read part 1, of this series, you may want to start there.
Some of you may have recognized in part 1 of this series that in the early days of supercharging, there are three types of superchargers - roots, twin-screw, and centrifugal. You may already be familiar with these buzz-words, but most people don't understand how each technology differs. Before buying a supercharger, you should familiarize yourself with how each type of supercharger works. Each has its own set of advantages and disadvantages that may make it ideal - or not - for your performance needs. Today we take a technical look at the technology behind each type of supercharger.
First lets begin with some basics. There are many components that go into making a complete supercharger system - mounting brackets, ignition controller, fuel pump, etc. In this article we look at only one component of a supercharger system - the supercharger itself (sometimes called a "head unit", "compressor", or "blower"). All superchargers, except turbochargers, are driven via a pulley that is connected either to the engine's accessory belt, or to its own belt that goes directly to a crank pulley. This is where the similarities between the different supercharger technologies end.
The Roots Supercharger (aka "blower")
The roots supercharger was originally designed as an air moving device for industrial buildings. The roots supercharger features two counter-rotating lobes that trap air from the intake side of the supercharger (normally at the back of the supercharger), move it around the outside casing of the lobes, and out the bottom of the supercharger through an outlet / discharge port. Like the twin screw supercharger, the roots is a "positive displacement" aka "fixed displacement" supercharger, meaning that it moves a fixed volume of air per rotation. Notwithstanding minor amounts of air-leak at low rpms, the roots supercharger cannot flow backwards like a centrifugal supercharger, and is thus nearly as efficient in its ability to pump air at low rpms as it is at high rpms. What this means is that roots superchargers are very capable of making large amounts of boost even when engine rpms are very low. This makes for great low-end and midrange power, and also makes them great for trucks and towing vehicles. The roots is also self lubricated, and is the simplest of the supercharger designs, meaning it is reasonably priced and very reliable. This is why roots superchargers have been the choice of GM, Ford, Mercedes, and Toyota for OE applications.
The only real disadvantage to the roots supercharger is that it creates a lot of heat. There are two reasons for this. First, the roots supercharger does not compress air - it only moves from the intake port to the discharge port (i.e. it is the only supercharger design with no internal compression ratio). All of the compression is done in the intake manifold. Laws of thermodynamics kick in in favor of supercharger designs with an internal compression ratio (centrifugal and twin screw) because they do less work on the incoming air charge. We will leave the mathematics of this phenomenon to a later (much more boring) discussion. Another reason roots superchargers create higher amounts of heat is because they tend to carry some of the compressed air in the intake back into the supercharger because it gets trapped by the rotating lobes that are exposed to the hotter air in the intake manifold.

A roots supercharger ("blower").

Want to know why a roots supercharger creates more heat than a centrifugal or twin screw? Calculate the amount of work each does on the incoming air charge and measure the area underneath the curve on the Pressure Volume Graph.

The Twin Screw Supercharger
The twin screw supercharger at first glance appears to look similar to a roots supercharger both inside and out. The two technologies are indeed similar, however there are significant differences. At the heart of the twin-screw supercharger are two rotors, or "screws" that rotate towards each other. The rotors mesh together and draw air from the back of the supercharger. The twisting rotors move the air to the front of the supercharger, while compressing the air before discharging through a port at or near the front of the supercharger.
Because the compression is done inside the supercharger, this design produces less heat than a roots supercharger - in fact, it is almost as thermally efficient as a centrifugal design. Like the roots design, the twin-screw is a fixed displacement supercharger (meaning that it pumps a fixed volume of air per revolution), and because the tolerances between the rotating screws are very tight, its ability to create boost at low rpms is unparalleled. These characteristics make it ideal for trucks and towing vehicles, where low to mid range power is primary in importance. Another important advantage of the twin screw compressor is its reliability. Unlike a roots supercharger, the rotors in a twin screw supercharger do not actually touch, so there are virtually no wearing parts. For this reason, twin screw compressors are commonly used to pressurize cabins in passenger aircraft. Like roots superchargers, twin screw superchargers are self lubricated and do not tap into the engine's oil supply.
One disadvantage of the twin screw design is that, because it has an internal compression ratio, the twin screw is compressing air even when it is not sending boost to the engine (i.e. under cruising or deceleration). An internal bypass valve releases the pressurized air, but because it takes work to pressurize the air in the first place, the twin screw supercharger draws more power from the engine than while not under boost. Like the roots, the throttle body must be placed before the compressor because it is a fixed displacement supercharger.

A cutaway view of a twin screw supercharger.

Airflow through a twin screw supercharger.


The Centrifugal Supercharger
Although the centrifugal supercharger is founded on a technology much newer than either the roots or the twin screw, it was the first supercharger to be successfully applied to automotive applications. Unlike the roots, the centrifugal supercharger is NOT a positive displacement / fixed displacement supercharger because it does not move a fixed volume of air per revolution. The centrifugal supercharger essentially operates like a high speed fan propeller / impeller, sucking air into the center of the supercharger and pushing it to the outside of the rapidly spinning (40,000 + rpm) impeller blades. The air naturally travels to the outside of the blades because of its centrifugal force created by its rotating inertia. At the outside of the blades, a "scroll" is waiting to catch the air molecules. Just before entering the scroll, the air molecules are forced to travel through a venturi, which creates the internal compression. As the air travels around the scroll, the diameter of the scroll increases, which slows the velocity of the air, but further increases its pressure.
The centrifugal supercharger enjoys several advantageous characteristics that make it the most popular supercharger design in the aftermarket world. First, it is simple and reliable because it has very few moving parts - just a few gears and the impeller. Second, the centrifugal supercharger produces very little heat because of its internal compression ratio. It is also small in size and very versatile because it can "free-wheel" and allow the engine to suck air through it or even flow air backwards. For this reason it can be placed anywhere in the intake tract - it can even "blow through" the throttle body, meaning it can be mounted nearly anywhere. It is also the most thermally efficient supercharger, meaning that it produces the lowest discharge temperature.
The only significant disadvantage of the centrifugal supercharger is that it must be spinning at a relatively high speed before it begins to make a significant amount of boost. For this reason, it is not helpful in creating boost (and power) at low engine rpms. Normally the supercharger only begins to create boost at around 3000 rpm, and the boost curve gradually and increasingly rises with engine RPM. Many centrifugal superchargers do not have a self-lubricating oil system, and draw oil from the engine's oil supply. The disadvantage to this is that you must tap the oil pan for the oil return line. However, in doing so, the supercharger becomes virtually maintenance free. Some manufacturers make a "self-contained" centrifugal supercharger that is self-lubricated like roots and twin screw superchargers.

A centrifugal supercharger.

Airflow through a centrifugal supercharger.

The Turbocharger
You may be wondering where the turbocharger fits in to this equation. Technically, a turbocharger IS a type of supercharger - one that is driven by exhaust gasses rather than from a pulley that draws power from the engine's crank. Because we have covered this topic in depth in our Turbos vs. Superchargers article, we will not re-examine the differences again here. Because the turbocharger relies on a technology substantially different from the three traditional supercharger technologies discussed above, it is beyond the scope of this article.
That's it for part 2 of the series - next time we'll pull everything together and discuss what goes into making a complete supercharger system, and how the supercharger works in conjunction with the engine.

flrtin1

Welcome to the 3rd and final installment of "Superchargers A-Z". If you haven't already read Part 1 and Part 2, of this series, you may want to start there.
So far in this series we've discussed what a supercharger is, where it came from, and what technolgies drive the core of any supercharger system - the supercharger itself. Today we'll take a look at the supercharger system as a whole. Because of the radical performance differences between a supercharged engine and a normally aspirated engine, the supercharger must integrate with other critical engine systems like the ignition system and the fuel delivery system. Don't worry, though, because almost all of the supercharger systems sold today are complete supercharger systems and do not require the addition of 3rd party fuel and ignition components. With this in mind, let's break a supercharger system down into its main functional components - a discussion of the supercharger itself is not included in this article because it was the focus of part 2 of this series. Keep in mind that each supercharger system is designed for a specific application, and the specific contents of different supercharger systems vary greatly.
The Air Intake System
Because a supercharged engine draws substantially more air than a normally aspirated engine, it is important to minimize intake restrictions. To ensure a smooth delivery of air to the supercharger, most supercharger systems include a high-flow air filter as well as low-restriction tubing or ducting to deliver air from the atmosphere to the supercharger. It is important to maintain a clean air filter to minimize the particles that come into contact with the supercharger's impeller, rotors, or screws. Most supercharger systems will draw air from behind the fender wall, where there is an abundance of cool air that has not been heated by the engine. Because superchargers heat air as it is compressed, a cool air supply helps to keep the charge temperatures at a reasonable level. On a non-intercooled application, the cold air pickup can lower the charge temperature by up to 60 degrees!
On most vehicles the incoming air charge passes through a Mass Air Flow sensor (aka MAF) on its way to the supercharger, although on centrifugal superchargers, the Mass Air Flow sensor can be mounted after the supercharger ("blow-through" setup). The Mass Air Flow sensor measures, you guessed it, the mass of air that the engine is drawing. This reading allows your engine's ECU (Electronic Control Unit) to calibrate and deliver the appropriate amount of fuel for the incoming air charge.
Once the supercharger has worked its magic, the air must be delivered from the supercharger to the engine intake. Although many roots and twin screw superchargers bolt directly to the manifold, most centrifugal superchargers require an extra tube called a Discharge Tube to carry the air to the intake through the throttle body. This tube will normally be mandrel bent to minimize restrictions.
The Bypass Valve
Compressor surge is a problem that affects most superchargers and develops when the supercharger is creating boost, but the throttle shaft is closed. Although not a problem on some low-boost (5psi or less) applications This condition can occur under deceleration or while shifting between gears, and can cause the car to sputter and chirp. Under surge, the compressor forces air into the closed throttle body until the pressure inside the throttle body is higher than the amount of pressure being created by the supercharger, and the air tries to pop backward through the supercharger. At that point, pressure is released inside the throttle body and the compressor forces air back through the supercharger and into the throttle body, which again has nowhere to go, and the process repeats. While surge normally is not highly damaging to the engine it is certainly annoying and can cause damage with time. To eliminate these problems under surge conditions, a bypass valve (sometimes called an anti-surge valve) is used to release the excess pressure. The bypass valve is actuated using intake manifold vaccuum, which opens the vent valve and releases pressure in the air-intake. Air is either released into the atmoshpere (blowoff valve) or recirculated back through the supercharger compressor (bypass valve).
The Intercooler / Aftercooler
Some supercharger systems include an aftercooler (more commonly called an "intercooler"). The purpose of the intercooler is to remove heat from the air to create a cooler, more densely packed air charge - more on this in Let's Talk Intercoolers, and Aftercooling - Vortech Style. Although the intercooler is not necessary on most street applications, its performance becomes increasingly important on higher-output systems (with correspondingly higher charge temperatures). The intercooler can be compared to a automotive radiator, only instead of cooling water or coolant, the intercooler cools the air. Air-to-air intercoolers force the air through a large air-cooled finned and fluted core, normally mounted in front of the car's radiator. Air-to-water intercoolers force the incoming air charge through a much smaller finned and fluted heat exchanger that is cooled by water. The water is, in turn, cooled by a compact radiator that mounts next to the stock radiator.
The two main purposes of the intercooler are 1. to allow more boost on a given octane level of fuel without detonation, and 2. to help create more power by condensing the air charge. Thus, intercoolers are very common on high boost applications (10+ psi) and on roots-style superchargers, where discharge temperatures are higher than normal. Most street supercharger systems (5-8psi) do not come standard with intercoolers.
The Fuel System
As increased amounts of air are pumped into the engine with the supercharger, so too must increased amounts of fuel be delivered. This is where the power gains come from. Most stock fuel systems are not up to the task of delivering the increased volumes of fuel demanded by a supercharged engine. Without a proper fuel system, your engine may run lean, detonate, and obviously perform below its potential. Because every engine is different, the fuel system requirements vary greatly with different vehicles and with different supecharger systems. Sometimes larger fuel injectors and a larger fuel pump is required. On some applications, a fuel management unit (FMU) will do the job by restricting the fuel return line to build up fuel pressure. On other applications, additional fuel injectors are mounted to the intake manifold, while on some applciations the stock fuel system works like a charm. Fortunately most supercharger systems include all of the fuel system components necessary to tune the engine to perfection. On some race kits, tuner kits, custom installations, and high output systems, it is up to the engine tuner to determine the engine's fuel requirements and tune the fuel system accordingly.
The Ignition System
The engine's ignition system serves the important role of telling the spark plugs when to fire so the compressed air and fuel is ignited at the exact right time to produce maximum power. Ignition timing can be advanced, causing the spark to fire earlier, or retarded, causing the spark to fire later. Ignition timing is critical not only for performance reasons, but also for engine longevity as it used to eliminate detonation (aka spark knock). With the added air and fuel that is compressed in a supercharged engine, the engine is closer to its detonation threshold. To avoid detonation, many supercharger systems retard the ignition timing, thus reducing maximum cylinder pressures and temperatures, and moving away from the detonation threshold. Because retarding the ignition timing causes a slight loss in power, a higher octane fuel or an intercooler are recommended for optimal performance, both of which allow for more timing without detonation. To ensure a complete and cool burn, high quality, cool heat range irridium spark plugs are also recommended for use on supercharged engines.
The Pulley
All superchargers are driven by a pulley that sits inline with the accessory belt or crank pulley. The size of the supercharger pulley is what regulates the speed at which the supercharger spins. Obviously, a smaller pulley turns the supercharger faster, and vice versa. The pulley is easy to change on all superchargers and is often used to increase (or decrease) the ouput of the supercharger. A simple pulley-swap can equate to huge power gains if the rest of the system is up to the task (in particular the fuel and ignition system).
The Rest
Other components serve self explanatory roles. Mounting brackets obviosly are used to attach the supercharger to the engine in a position such that the pulley can be spun from the accessory belt or an additional supercharger belt. The belt tensioner keeps the belt tight around the supercharger pulley, which is important to avoid slippage, especially on centrifugal superchargers which spin at high RPMs. Hardware, hoses, and fittings are of course necessary to attach the supercharger to the engine, connect the oil and fuel lines, and to install the ignition components.
That rounds out the complete supercharger system. Remember that every supercharger system is designed to meet the specific needs of the engine, given the desired level of output from the supercharger. For this reason, some supercharger systems come with only a few of the components mentioned in this article, while others come with it all. Generally speaking, higher output supercharger systems come with more components to meet the increased volume of air, which is why they cost more than entry level systems. Congratulations if you made it through all three parts of this series - you deserve a gold star and are now a supercharger expert!