School Project

[94green1le]

For my final project in my technical composition class, I am writing about the differenced between Roots, Screw-type, and Centrifugal superchargers. I got most of it complete and was looking for something that I believe would be a good visual aid. Does anyone know if any magazines did a side by side by side comparason of the same car, same motor, same mods, with the only difference being the type of blower? I would like to put the 3 dyno graphs side by side to give a visual of the different torque/horsepower curves and peak numbers.

Thanks in advance.

 

[mellor_21]

i KNOW one did like three or four months ago, maybe mmff?

 

[Stang849]

MMFF did do that a few months ago, they included a turbo set up also in the comparison. I don't remember if they had dyno graphs though in the article

 

[James Snover]

Superchargers, subject very near and dear to my heart.

All supercharger types, Roots, twin screw, and centrifugal are about the same age. All were designed in the late 1800's. All were initially designed for non-automotive purposes, such as clearing poisonous gasses from mines.

Twin screws were difficult to make, only recently have advances in manufacturing made them more economically viable.

Centrifugal compressors need speed or size to operate effectively, making them expensive and rare until the 1960's. For any size of centrifugal compressor, the faster it rotates, the more air it moves. So at low speeds, it may provide no boost, at mid-engine speeds it may still only be providing minimal boost; but at higher speeds it provides a very great deal of boost.

Roots blowers and twin-screws do not depend on speed to move air; they move the same amount of air with every rotation. This makes them ideal for low-rpm torque applications.

Roots type are the least efficient, and do not inherently compress air; any increase above atmospheric pressure is just a side effect. But a very useful one.

Twin screws are more efficient than Roots type, and they do compress the incoming air. This is partly responsible for their higher efficiency.

Centrifugal compressors are the most efficient of the three, and they do compress the incoming air. They are dependent on high rotational speed to create boost, in the typical automotive application, due to their small diameter. These favor high-rpm/ top-end power applications.

Centrifugal compressors can be made very large, and thus spin slowly, and make high boost. But we are talking several feet in diameter, up to many tens-of-feet in diameter.

All compressors heat the incoming air. This is an inescapable consequence of pressurizing any gas. In an automotive application, the less you can heat the incoming air, the better, in general. Roots types heat the air the most, Twin screws are second, and centrfugal compressors heat the air the least. But all of them heat the air.

There is one other type of compressor that has not seen much use in automotive applications: the axial compressor. Basically, the front half of a gas-turbine engine is an axial compresor. These can be very efficient, and heat the incoming air the least of all the types discussed, and provide very high boost. But they require high rotational speeds, and in a very specific window of speeds. Below or above the most effective speeds, they quickly become very inneficient. Axial compressors are very expensive, even with today's manufacturing capabilities. There was only ever one that I know of, made and sold in the early 1980's, and I can't remember the name of it. It did not gain any significant portion of the market.

And that's about all I can recall off the top of my head at the moment.

There is one particular type of engine that uses a positive displacement blower to increase fuel economy: a Miller-Cycle engine.

But that is a whole different subject.

Jim Snover

 

[James Snover]

Also: for a _great_ reference on supercharging, look for Corky Bels book, "Supercharged." It is available at most of the big chain book stores, and it is one of the best books ever on the subject.

Jim Snover

 

[lukabrozi]

wolfram alpha answers all questions

wolfram alpha will answer your questions.

Wolfram Alpha Computes Answers To Factual Questions. This Is Going To Be Big.

It will be up and running soon and they will give you answers that google etc. cannot come close to.

 

[PonyFever]

Supercharger Types Comparison

No dyno but it is a chart, and charts go over big on technical papers, no? Good luck.