Roots vs Centrifugal

[falconGSR]

After taking a look at the SCC article regarding the Vortech supercharger, I have crossed it off my list as a potential forced induction solution.

I didn't realize how much you had to spool that thing up (just like a turbo) to get it pumping air. It seems like there's alot of rotating mass inside there between the main rotor and the gearing to step up engine RPM to over 20k RPM.

The consequence of this is the torque curve looks ridiculously steep, peaking at redline. Since I am not interested in drag racing or subjecting my motor to that sort of boost at 8k RPM, I'll take the losses associated with a Roots charger since it will move my torque curve up, instead of tilt it.


I would imagine the Vortech's sloped torque curve completely changes the way you would drag race, since you're always looking to pull into redline. Maybe thats why their 1320 numbers aren't so great for an advertised 272 HP.



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Bone stock GSR, advanced timing for cold weather, oh and those clear bumper lights santa brought.

[Joe/UK]

Woah! - put away the cheque book.

Eaton / Roots Suck unless you are keeping to the 5 - 6 psi range. What we all need is a Lysholm screw blower. What does it do differently? - in a nut shell, it is almost twice as efficient as a Roots blower, which means MUCH lower intake temperatures = denser air = MUCH BIGGER POTENTIAL HP.
Counter rotating Lysholms are now appearing in the market place, so dont go sponsoring the existing half assed "Kits".
My .02.

[This message has been edited by Joe/UK (edited December 28, 2000).]

[Team Hostboard]

I brought up the issue of rotating mass to Trevor at Vortec and talk about completly avoiding the topic, the best answer I got was the blower makes more HP then it takes to drive so it is not an issue.

...Steven

[Team Hostboard]

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by Joe/UK:
Woah! - put away the cheque book.

Eaton / Roots Suck unless you are keeping to the 5 - 6 psi range. What we all need is a Lysholm screw blower. What does it do differently? - in a nut shell, it is almost twice as efficient as a Roots blower, which means MUCH lower intake temperatures = denser air = MUCH BIGGER POTENTIAL HP.
Counter rotating Lysholms are now appearing in the market place, so dont go sponsoring the existing half assed "Kits".
My .02.[This message has been edited by Joe/UK (edited December 28, 2000).]<HR></BLOCKQUOTE>

Well your almost right. The Eaton M62 be design is capable of 10psi give or take a little. To go further you need to elist the help of a company like Endyn. Then you should be good upwards of 15+ psi

[falconGSR]

I was about to ask where to learn more, but a web search provided this:

Info on Lsyholm and other types of forced induction -
http://www.turbotechnics.com/supercharger/expo.htm

Low specific-speed devices without internal compression, relying on ?back-compression? to raise the pressure of the pumped air. The commonest example is the Rootes blower, which has been in use for very many years, and is still the dominant type today. Its greatest strength is its comparative simplicity of construction, combined with reasonable performance at low speed. However, reliance on back-compression means that efficiency will always be poor, resulting in a high drive power requirement and elevated air outlet temperatures. The low-speed nature of the compression process means that this class is inherently bulky, leading to installation difficulties.

Low specific-speed devices using internal compression, common examples being the Lysholm screw-type compressor and the G-Lader. The use of internal compression makes these types significantly more efficient, although they still suffer from substantial bulk. Their natural characteristics display good low-speed performance, although this depends in large measure upon maintaining very close clearances between the moving elements, presenting considerable manufacturing problems.

High specific-speed devices, using a centrifugal compressor, characterised by high adiabatic efficiency. The impeller is similar to that of a turbocharger and requires to be run at 15 to 20 times crankshaft speed. A variety of types are in use, most commonly using a step-up pulley drive followed by a high ratio gear drive, to produce the required speed of perhaps 140,000 rev/min, depending upon impeller size. Because the compressor operates with high gas speeds, it is inherently compact, but as its speed is linked to the crankshaft, the natural characteristic is to deliver a rising boost pressure with engine speed, rather different from the previous types.

[Marc]

If you're interested in learning more about superchargers there is a great book called "Street Supercharging" by Pat Ganahi. YOu can find it on Amazon.com

It's geared mostly towards domestic applications but there is a great chapter that compares and contrasts the different types of blowers most notably roots vs. centrifugal


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Marc
1997 Civic EX
The supercharger is gone. Get ready for the turbo.
Want to know why I got rid of the JRSC? http://crx.honda-perf.org/horror/jrsc.html