Many members of this forum don't seem to realize the difference between superchargers, so I made this thread to help explain.

4 types:

1) Turbo (yes, technically a supercharger)
2) Centrifugal
3) Roots
4) Twin-screw



1) Turbos are the most common on stock cars including the Bugatti Veyron 16.4 - a 1.3 million dollar car with 16 cylinders and a 0-60 time of just 2.3 seconds! They are powered by a turbine in the exaust which is pushed by its flow sort of like in a jet engine. There is lag before it starts which is usually around 4,000 RPM but differs depending on size of engine and size of turbo. Also, turbos tend to lose power in high RPM. Turbos are the most dangerous for the engine with mods since they usually produce too much pressure for the engine (not with RX-8 though). There air coming in is extremly hot and turbos need intercoolers to cool down the incoming air. Turbos are usually hard to install and are likely to eventually break, but usually repairable. Also, they are quiet, but loud enough for you to hear the turbo spinning.

Summary: lag/requires intercooler/quiet


2)Centrifugal superchargers give pulley driven forced induction a bad name. I have never heard of this being used on a stock car, but the Taurus HSO might have. They have lag like turbos and are shaped like them too. Surpisingly low amount of heat produced. Intercooler is not required. These are basically exactly the same as turbos except generally easier to install but require large amounts of horse power to be driven. These are not recommended, buy the turbo instead.

Summary: lag/no intercooler/loud


3) Roots style are very uncommon on stock cars. The only car I can think of is the Lotus Exige 240R supercar - which is a very nice car and is probably the best nadling street legal car since it weighs around 1,500 pounds. The roots style has basically no lag. This means even if it doesn't produce as much top horsepower as the above chargers, it could and usually is faster while racing on a track with turns. Roots-style superchargers are very loud and can break. Also, they send in hot air so intercoolers are needed to cool the air off. Like turbos, roots tend to lose power at higher RPM. Installation can be the hardest of the four. You can adjust how fast they spin but too slow means you don't get as much power and too fast tends to be the same. Also, roots take up around a third less than centrifugal but still take up over 10. Unless you like the noise, twin-screw tends to be a better upgrade.

Summary: no lag/requires intercooler/loud

4) Twin-screw is probably the best type. These are used in very fast cars with forced induction such as the Ford GT. They have no lag and the air stays cool when moving through it. They are quiet and can't spin too fast unlike the roots style. Also, twin-screw compresses air within the charger while roots tries to compress it after moving through it. Twins typically only use around 5 horsepower while giving more than roots. In higher RPM, twin-screw keeps putting out the same power unlike the others. In the way twin-screws are designed, the blades do not rub against the sides so they very rarely break.

Summary: no lag/no intercooler/quiet


PSI:
This is what fools people. Just because it has more PSI doesn't mean it puts more air in. PSI is the measurement of PRESSURE. If the air is cooler it takes more air to make the same PSI of hot air since the particles are closer together in the first place. The best way to seem the most horsepower is to see what the manufacturer lists (we are lucky because they do for the RX-8).

Which is better for engine?
Since twin-screw superchargers put in cold air with less PSI to make the same gain of air in the engine - it is for most of us. However, turbos aren't always on so they are better stock on vehicles. But, since it costs $3,000 or more for forced induction, most people who get it drive in high RPM everyday so the turbo would be worse.

 

good writeup. Now, how much did the twin-screw corp. pay you for plugging them?

 

Wow, there are so many inaccuracies I don't know where to start.

 

Axial flow.

linear boost response. less "lag" than centrifugal. less top end than centrifugal. potentially the most efficient of the bunch.

 

First let me say I'm happy to see a young man starting to do research on supercharging. Having said that you might not want to come off like the authority on it. Just about everything in your post is wrong.
Instead of reading magazines you really should read textbooks. Then you can quote with some real information.

I think this forum has a good education on superchargers and they have tons of threads constantly going over these facts. I know this because I debate it all the time here. Not to beat my own thread (drum) but you could get a better education by reading just the first 25 or 30 pages of "Axial flow supercharger" even just the first 10 pages will tell you more then you already know.

Keep up the research, just dig deeper into engineering facts and stay away from the magazines.

 

Turbos are for certain the best for top end (if you size it for that of course).

There are plenty of stock cars with roots chargers on board; Pontiac GTP, Jaguars (Can't remember the kind), a few different Chevy's, Ion Redline... Just to name a few :wink:.

It is very good to do research. I have a book on the principles of FI, and I learned A LOT from it. Like RP said, go out and get one or two. It is good reading, and you will learn a lot.


Twin screw superchargers are very nice though.

 

ok so since we're teaching each other here .. i just posted this question in another thread .. if all you need is high pressure why not have a home depot compressor with a can and control the release of air PSI/density/whatever into the engine .. last time i checked we had electricity in the cars and you wouldnt have to deal with all the mechanical bullshit .. just plug a hose in your intake .. so book worms can you set me straight here

 

because compressor tank is heavy + it'll only last a second after charging it for over a minute. additionally... such thing exists., except that instead of compressed air, you have chemically bound oxygen in a tank. it's called a nos. maybe you've heard of it.

the closest novel idea i think would be electric supercharger where you use electric motor to blow air into the intake with a propeller. the e-supercharger on the market right now is a joke... but as technology advances, i'm sure we can make an electric motor strong enough to generate the kind of compression turbocharger & superchargers are capable of today. if you think about it, it'll be great!!--light weight, constant boost all the time at a flip of a switch... what more can you ask for?

 

well the tank i just a reserve .. and i dont know how much air in terms of volume engines suck in .. intake pipes look pretty big so i guess you're right that it would eat the tank in a few seconds even if the pressure of the tank was several times higher than whats needed in the engine

to me the whole idea of turbo/supercharges is just overrated because of lack of portabiity and hence a high cost .. every turbo/sc has to custom made to a car because of mechanical mods

if you had an e-charger as you call it .. or even another small 300cc engine pumping air at a flip of a switch .. you could make thousands of them with instructions put in trunk .. plug hose to intake .. flip switch to rx8 (or it comes preprogrammed when you buy) and the price should probably be a third of what turbos go for now

 

Over ambitious

 

Your typical home deport air compressor can only output 5cfm. An NA Renesis breathes 400cfm.

 

So... Basically your saying that: you should have a small motorcycle engine in your trunk to compress air that would be routed to the front of your car to power that engine? So thats about a new 2.5" pipe running from your trunk to your engine. And the trunk engine would have to be carefully matched to the front engine to provide the correct amount of air at the correct RPM.

In essence, you have an egine powering an engine! But wait, why can't we just use the car's engine to provide the same effect?! We could have the car's engine power the compressor directly and cut out the middleman!!! Genius!

 

These things have been tried. GM tried a big oxygen type bottle pressurized to thousands of pounds pressure. It didn't last long and the onboard compressor took hours to refill it.
Next someone tried a six cyld engine with one cyld not firing but used to compress air into a bottle.

Nothing is really new.

"You just keep thinking Butch, that's what you're good at"

 

A good place to start researching superchargers/turbochargers is http://auto.howstuffworks.com

That site has some real basic but accurate information.

 

In order to be 100% accurate, I'd have to write a book so I'll do the best I an to correct much of this without getting TOO long and hopefully I want leave out too many details in the process.
5 types. Don't forget the axial flow.

As you stated turbo lag depends on the size of the engine or the turbo. More accurately it depends on the size of the turbo. The size of the engine is irrelevant as long as it hs a properly sized turbo for the job at hand. In addition to this, the lag time also can change based on load level and what gear you are in. Throw a turbocharged car in 5th gear at 25 mph and floor it. See how long your lag time is. You can time it on a stopwatch.

A turbo will only lose power at high rpm's if they are too small. This isn't the fault of the turbo and has nothing to do with it's compressor design in theory. It is just sized improperly.

Any device that compresses (and some that don't!) air will heat the air up. A properly sized turbo can actually be quite efficient compared to many of the other types of forced induction out there. To say that they necessarily need an intercooler is not necesarily true. No form of forced induction always needs an intercooler. If you re runing low boost levels, it may not be necessary. An intercooler will cause a slight pressure drop. At low boost levels the pressure drop may be greater than the amount of gain that the intercooler adds back in. Even if they come close, the added distance in the piping causes an increase in lag time. It is only above certain levels that you absolutely need an intercooler and this applies to all forms of forced induction. Some forms of FI need it befor others in order to get to certain power levels but again this too depends on many other factors which I am not going to get into there.

Not al turbos have bad lag, some do. Not al turbos are loud. Not all turbo setups require an intercooler.

Since the compressor design is similar to a turbo, the heat from compression is also similar. They are actually quite close in efficiency in this regards but there are many forms of efficiency that apply here. Again as with a turbo an intercooler is not always necessary but wil be at some point. I'm not going to get into the amount of power required to turn these devices but it is considerable in some instances.

The boost curve rises with rpm but is not linear. Depending on the internal gearing of the unit boost may rise with the square, cube, or greater the speed of the engine meaning any considerable boost is being mae at higher rpms only with little to no gain at lower rpms. Again I'm leaving out alot of detail but hopefully the point gets across.

I'm not quite sure why you think a roots style supercharger is uncommon on stock cars. It is extremely common and is currently used on cars from Ford to Mercedes. Eaton superchargers are the most common and they are roots style superchargers. With the exception of theFord GT and the Meredes SLR, nearly every other supercharged car from the factory is a roots.

An advantage of the roots is that it is a simple device that doesn't spin as fast as most other types out there. This makes them very reliable. New roots superchargers are also fairly quiet. This type of supercharging is gnerally accepted at the least efficient form out there but even this needs to be quantified. A properly sized roots blower can be more efficient and more powerful than an improperly sized turbo. There is so much more to it than just yes and no. They may lack the total system efficiency of a centrifugal system but their added boost at lower rpm's would make them more powerful down there. You get the idea. We can keep coming up with examples like this all day both for and against them.

The air is hotter since there is no internal compression ratio. Of all the types of forced induction, this is the only one that does not have an internal compression ratio. It literally blows air hence the nickname, "blower". This means that air in the manifold backs up which raises it's pressure. The rotors of the roots blower basically beat up the air in the manifold. This is more work to keep it there and more work being done to the air heats it up more.

Roots do not always have poor top end power. They can be made to get good top end power but there is always a tradeoff to do this. I'm not going to get into it here.

Does it need an intercooler? I think I answered that above. It depends.

Air does not stay cool in a twinscrew. It compresses it which heats it up. It is cooler than an equally sizes roots blower though. They are far less common in production cars due to cost. Yes the Ford GT has one. That car has also been discontinued. The Mercedes SLR also has one. Mercedes has also stated that by 2008 they wil no longer use any superchargers. They will only use turbos. Richard don't get technical about terms on me!

Not quite sure where your horsepower usage number came from but that too depends. Let's just stay simple and say you are way off in so many ways.

Twinscrew superchargers are nice units but as with every other type, they have their place. No form of turbo/supercharging is always best for very situation. I'm not going to get into any real detail about twinscrews since there is already alot of information about them elsewhere.

I agree that pressure is misunderstood by many. It is flow that is important. Cooler air and hotter air contain the same amount of molecules. You can't make more from nothing. Don't confuse heat with pressur and flow. You've got this messed up.

Which is best for the engine depends on many factors. It depends on how much power you want and what type of use it will primarily be for. I can think of different situations where I would want different roms of forced induction.

I'm not going to get into the axial flow here because it has it's own thread.

 

It's Taurus SHO, not HSO, and they were not supercharged, at least none that I've seen or read about. It used a Yamaha V6.

 

There way more than 4 or 5 types of superchargers - probably a few dozens. However most aren't particularly popular, but at least the 'G-supercharger' from Volkswagen was somewhat popular (and has not been mentioned).
And don't forget the Comprex system (pressure wave supercharger), which was even applied by Mazda and might become more popular in the future since it is more effective if the Comprex drum is electronically controlled and electrically driven.