lefuton

can anyone explain to me the difference between different kinds of superchargers...cause i've read here and there and seen some people mention centrifugal and other types but am yet unable to distinguish the difference.

tia
-nate

wakeech

well, there are three basic types of superchargers: roots, "screw", and centrifugal.

the roots type is what's most commonly referred to as a "blower": it's basically no different from a generic pump, with two interlocking impellers which spin at the same speed and pump air through...

the "screw" type (someone say the real german one, i just got back from work and can't think) which is a variation on the roots type: two different interlocking screws, with different numbers of blades, spinning at different speeds... the idea here is the same as the roots (they just pump air through), but the two different screws have maximum efficiency at different engine speeds, so you're getting more effective boost throughout the rpm range.

the centrifugal type is a little different: it has a turbine-esque impeller which draws air in, and propels it toward the engine at a higher speed than it draws it in at.... really, this is what a turbocharger is, but turbos are exhaust driven, rather than pulley driven (off of the engine's main shaft pulley).

cool link: http://www.miata.net/garage/turbos.html

lefuton

that's awesome, tnx for the info...guess now i gotta find out what the difference between turbos is hehe

CraziFuzzy

basically, a turbo is a turbo.... basically... two rotors on a single shaft, exhaust spins one, which turns the other, which pumps the air... The differences in Turbos lie in the size, and the arrangement (Single, Twin, Sequential, etc.), The benefits of Twin and sequential, is the ability to get the same airflow at the same boost, without the extreme lag that a single BIG turbo causes... basically a case of more inertia to spin up.

Supercharger

http://www.superchargersonline.com

Jreyenga

not quite right about the screw compressors though.

A roots blower just blows air, which in turn is compressed because it is trying to blow more air than the engine can suck, which is very ineffecient. One big reason that a roots blower is inefficient is that the lobes trap air at atmospheric pressure at the inlet, but as the lobe moves that air to the exit it is suddenly exposed to higher pressure air(due to the buildup of flow), this higher pressure air then goes back into the supercharger before being blown out, which is very inefficient.

A screw compressor is very different. It has a male and female screw that actually form a chamber which gets compressed before exposed to the exit. A screw compressor has an internal compression ratio, so if it's operating so that the exit pressure is near to the pressure built inside the compressor it will be at peak efficiency. If it is anywhere near that point it will be much more efficient than a roots blower, which means less power to drive and less heating of the air.

I don't have any good sources to go to for a better description of this, but howstuffworks.com may have some drawings and such.

The moral of the story is a roots blower just blows air which happens to get compressed, a screw compressor compresses air, which it also blows.

Man I wish I could afford a screw compressor for my miata.... oh well... time to continue dreaming.

wakeech

ah, i knew i didn't have my story straight... thanks :D

Supercharger

Twin-Screw Supercharger:

sKy^WiNGzErO

I kinda work on aircrafts, so i see this pretty often, but just thru SHEER curiousity, what would be the effect of putting a dual stage centrifugal (double entry impeller) compressor on to one of these lovely rotor motors (or nornal piston ones). Bear in mind, this is like 10:1 ratio, or there abouts and that this is for each impeller.

wakeech

great pic supercharger.

Jreyenga

Kablooie or nothing

If, and this is a big if, you didn't get detonation(big *** intercooler and water injection and running on ethanol and like 7:1 or lower compression), it might not still work because you'd spend soo much work compressing the gas and only have that 7:1 or so expansion with the piston to generate work. 10:1 volumetric compression takes a fair bit of work, to put that in other units that would 370psi of boost, which would also mean a pretty big compressor to flow that much air at that level of boost.

If you wanted to make sickening amounts of boost, you have to go with a turbo, otherwise you start loosing too much power through the compressor.