What exactly is the difference between the two? How do both of them affect a car's performance?
Thanks
Tim

Supercharger - compressor for intake air directly driven by mechanical means, such as a belt.

Turbocharger - compressor for intake air, indirectly driven by exhaust turbine.

Supercharger usually has no "lag" from throttle opening to achieving manifold boost and increased power.

Turbocharger has a lag until the turbine can accelerate and produce boost pressure. Many turbo's have very little lag now.

Supercharger boost is proportional to engine speed. Ultimate boost may be regulated by a wastegate.

Turbocharger boost is proportional to engine speed squared. Tubo's are sensitive to specific engine application. Ultimate boost must be regulated by a wastegate.

Supercharger uses mechanical horsepower from the shaft, lowering net power by a fractional amount.

Turbocharger gets its power from waste heat in the exhaust, and does not lower net power.

all such forced-induction systems are rightly called superchargers because they force an intake charge into the engine above what can normally be done with normal aspiration - hence "super"-"charging". Forced induction improves the volumetric efficiency of the engine, allowing it to take in more intake air.

a turbocharger is a supercharger that uses a turbine to drive the compressor. That turbine is driven by the exhaust gases, in normal practice, to put to good use the unused energy of the exhaust gases. The compressor itself is typically a centrifugal fan. What we know as a "turbocharger" is therefore an exhaust-driven supercharger.

all non-exhaust-driven forced-induction systems are therefore referred to as plain "superchargers". Most of them are driven from the engine (someone has mentioned an electric drive as well), and the compressor may be centrifugal, roots-type or screw-type.

there is another type of "supercharging" that does not have moving parts - ram air forced induction - where you use the high pressure at the front of the car as it moves to compress the intake air.

although a "turbocharger" uses the energy of the exhaust gases and does not rob power (directly) from the engine, it does impose some backpressure in the exhaust system, limiting power a bit - but this is negligible compared to the gains in volumetric efficiency due to the compressed intake charge. However, since the turbine itself has a silencing effect on the exhaust gases, a less restrictive muffler system may then be used, to comply with noise level regulations.

Depending on noise levels, with a turbocharger, it's actually legal to run with no muffler at all.

On some engines, a straight-piped turbo diesel is actually quieter than a naturally aspirated version of the same engine with a muffler installed.

At least in CA, assuming noise levels aren't violated, all you need in your exhaust system is a restriction of sorts. A turbocharger counts as such.

Also, there are some turbochargers out there that are not wastegated. Those turbos are usually designed to never be able to put out more boost than the engine can handle, which also means that the amount of boost put out at the low end is usually pretty bad...

Excellent explanations for a good question.

__________________
1983 380SL
1995 C280
1995 S500 coupe
1990 Mazda Miata
2004 Suzuki Hayabusa

A centrifigual blower is similar to a turbocharger (okay, fine, "exhaust-driven supercharger ). You have a disc with vanes sticking out of it, and the vanes suck in the air and push it out into the intake.

A roots blower (this is the one I'm most used to; they're standard {and required} equipment on two-stroke Detroits) looks like two Y-shaped pieces that are longer than they are wide. One is on top of the other, and they're made to mesh in with each other (they come real close to touching, but don't actually touch). On Detroits, these blowers are actually gear-driven (if the blower stops, the engine doesn't work since there's no way to get fresh air in and the exhaust out), but they're belt-driven on most other applications.

The screw-type...I'm waiting to hear about this one too. I've never heard of one before.

Isn't a screw type what Mercedes use, at least in the V8? It makes no supercharger whine - why?

__________________
190E's:
2.5-16v 1990 90,000m Astral Silver
2.0E 8v 1986 107,000m Black 2nd owner
http://www.maylane.demon.co.uk/190esmall.jpghttp://www.maylane.demon.co.uk/190esmall2.jpg

there is no whine because the rotors are teflon-coated

"there is no whine because the rotors are teflon-coated"

Supercharger whine is caused by the drive gears. Usually, blowers with straight cut gears are very loud and ones with helix gears are rather quiet. Noise has nothing to do with the teflon coating. The Mercedes blower, I'm sure, is engineered to be as quiet as possible.

Here is a pretty good explination of the different types of superchargers:
http://www.sportcompactcarweb.com/tech/0107scc_garage/
http://www.autospeed.com/cms/article.html?&A=1102

Twin-Screw:
http://www.whipplesuperchargers.com/product.asp?ProdID=1162

This is from the literature about the C32 AMG: http://mbspy.bacosys.be/w203c32.htm :

"The newly developed V6 engine uses a positive-displacement, Lysholm-type supercharger with scrolling aluminum rotors, providing usable boost virtually from idle speed. The rotors are also teflon-tipped for more positive sealing, quiet operation and long life. "

How would teflon coated rotors make for quieter operation. The non-teflon coated rotors don't make contact with each other so how would this have any effect on noise?

The noise from a supercharger is caused by gears. At idle a straight cut gear will make a rattling like sound. That is from gear slack in the nose drive. Superchargers that use straight cut gears in the nose drive are louder at idle than those that use helix gears. At idle there is no load on the gears - they tend to rattle back and forth a bit and that presents as a rattling sound. The sound will dissapate as the engine is rev-ed up just above idle and will turn into a nice whine when there is a load on the gears. This is all very normal. As the supercharger ages the rattle sound at idle may get louder. Worn pulleys and belts as well as mis-machined pulleys can also contribute to blower whine.

A "standard" roots blower has straight rotors that intermesh -- some are two, some are three, there may be some four , lobed rotors out there. They all work the same way -- positive displacement, like a gear type hydraulic pump.

A "screw" blower has the rotors "twisted" rather than straight. Harder to make (hence more expensive), but the air delivery has considerably less pulsation and is much easier to maintain laminar flow in (dragsters use screw type blowers). I don't think anyone is making straight rotor blowers anymore.

Root's blowers have been around forever -- since the early 20's anyway (the Bentley "blower", for example). Benz made one in the 30's with the blower clutched in by the accelerator pedal -- past halfway down or so, you instantly got an extra 60 hp. My friend Hans said it was quite an experience to ride in (on a wooden box, no seats -- Rommel's staff car, I believe). Tossed a main bearing on that trip and ended up junked, I think -- this would have been about 1951 or so.

Due to the bearing loads and the tiny clearance on the blowers, Roots type blowers don't last as long as turbochargers, and are more expensive to make. They also tend to produce a fixed raito of boost to atmospheric pressure unless you have a rather more complicated control system than a spring loaded wastegate. A turbo will increase the boost "automatically" as the load increases, and a blower won't.

A centrifugal supercharger will move more air at higher speed, but output is then pretty much regulated by engine rpm, not load. The ones used in aircraft were often two speed (low altitude/high altitude) and had some means to control the amount of boost generated. Not a problem in an aircraft (four or five handles on the "throttle quadrant"), but kinda complicated in an automobile. To get boost when desired and not at other times requires some other system.

Mechanical superchargers in cars always strike me as gimicky -- you can get everything but the near instant power with a turbocharger at much less direct cost, and with considerably less complexity (and later cost when it bites the dust).

None of us are racing, just driving to work or for pleasure, and instant throttle response isn't exactly a necessity.

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

supercharging and turbocharging became widely used around world war 2 and the piston-driven turbo (like in cars today) served as the basis for the jet engine. The 'invention' of the jet was one of those events that lead the industry to wonder why it hadn't been developed sooner....One of the problems with the piston driven engines is that they require high test fuel--- jets run on really low grade fuel.

this also makes on wonder why certain long-haul vehicles (tractor trailers) do not make use of jet propulsion rather than using internal combustion piston-driven diesels.

Jet engines don't like varying loads, they use way more fuel at idle (compared to a diesel) and they are very, very expensive. However, when money is no option (or it's someone elses) they are used (like in an M1A1 or A2 tank).

__________________
1982 Mercedes-Benz 300CD
1982 Mercedes-Benz 240D - stick

While the prinicple of a jet engine is simple, the applications are not. Takes an awful lot of engineering (and research to get the knowledge to do the engineering) to get one to run. Lots of money, too.

An internal combustion engine is fairly easy in comparison -- if you can valve the cylinders, it's not all that hard to squeeze the fuel/air mixture, ignite it, and trap a useful amount of energy from the resulting hot gas. In a jet engine, you must aerodynamically compress the air, spray fuel in, and expand the hot gasses through a turbine the extract any usefull heat, and until you stick a propellor or big fan on the front, the efficency for propulsion is simply horrible below the speed of sound -- at that point, you don't have to work very hard to compress the air. At zero air speed, a straight turbojet (no prop, no fan, all the air goes through the combustion chamber) uses more than 90% of the energy developed by burning the fuel just to compress the air coming in!

Most of the early jet engines had centrifugal compressors just like a turbocharger, and a goodly number of them had a similar turbine setup. Whittle's engines did, the De Haviland Ghost did (some even used both faces of the impellor to compress the air), even some of the German engines were centrifugal. The ones used on the ME262 were axial, both compressor and turbine, and the only reason the turbines lasted as long as they did was that the Germans found a way to bore holes in the blades to push air from the compressor out the blades to cool them. NOT a simple process to design, nor simple to manufacture.

There are also considerable balance problems to overcome -- a device weighing several tons with a rotating section over three feet in diameter going 20,000 rpm will dance all the place with even a slight imbalance! GE builds them with the shaft vertical to prevent bending it during manufacture.

The oils used are critical, too -- successful jet engines really required the development of synthetic oils. The Germans were ahead on that game, too, not entirely by choice (no petroleum). Mineral oils simply will not do the job. Been used since the late 40s.

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!