screw type - roots type...what does this mean?

[sodaking663rd]

i hear lots of talk about screw type blowers, roots type blowers and centrifugal blowers. can someone explain the differences and give some examples of each? i'm pretty sure the centrifugals are the popular vortech/paxton types but other than that i am at a loss. thanks!

 

[5.0 con-vert]

Roots type blowers use interlocking identical lobes that pushes air into the intake manifold where it is compressed, or "boosted". Once positive manifold pressure is achieved, it can cause some blow-back into the compressor.

Centrifugal type blowers are virtually belt driven turbochargers. They need time to spool up and deliver their boost higher in the engine rev range.

Screw type blowers compress air in the blower housing itself, as well as in the intake manifold. They use male / female screw shafts that never touch but have extremely tight tolerances, minimizing or eliminating any blow-back into the supercharger housing after boost is achieved. Screw type blowers have greater adiabatic and volumetric efficiency over the entire operating rev range than do Roots or Centrifugal blowers.

i think

 

[sodaking663rd]

thanks for the clarification

 

[87'GTstang]

Pretty much. Manufacturers for years have stuck to roots because they are about the most trouble-free and worry free design. Twin screws are the new wave of roots-style superchargers. They are as described above but boast greater efficiency and lower discharge temps. Install for both are virtually a breeze.

Cetrifugals have the possibility or providing more power potential in the upper rpm range than the rest, but it is all really relative. Twin screws along with roots have instant power from idle up because they are positive displacement designs meaning they shove the same amount of air per revolution into the engine per given rpm due to the design. Centrifugals need time to build boost. Both have disadvantages and advantages but the popularity goes to the centrifugals. However though, twin screws are greatly coming up in attention recently after being kind of shunned upon for years. A lot of it has to do to the great and flat torque curve they put out and that they can put out lots of it on demand. People will say they run out of "oomph" in the upper rpm range, but the otherside of it can be said that while the centrifugals are "spooling" up and working on building power, you already have the other designs pumping out a lot of power at almost their full potential up from idle. So really it's kind of a game of catchup as to where one passes the other and where you want the power.

Again, like anything else, just what tastes you like.

 

[Daggar]

Roots type blowers use interlocking identical lobes that pushes air into the intake manifold where it is compressed, or "boosted". Once positive manifold pressure is achieved, it can cause some blow-back into the compressor.

Centrifugal type blowers are virtually belt driven turbochargers. They need time to spool up and deliver their boost higher in the engine rev range.

Screw type blowers compress air in the blower housing itself, as well as in the intake manifold. They use male / female screw shafts that never touch but have extremely tight tolerances, minimizing or eliminating any blow-back into the supercharger housing after boost is achieved. Screw type blowers have greater adiabatic and volumetric efficiency over the entire operating rev range than do Roots or Centrifugal blowers.

i think

This is a Great "nutshell" description! Great post!

 

[darthcual]

I believe that this actually refers to the type of Kung Fu you are using. Example: "My screw type kung fu will beat ur tiger style!" and so on and so forth.

 

[TheUser]

I believe that this actually refers to the type of Kung Fu you are using. Example: "My screw type kung fu will beat ur tiger style!" and so on and so forth.

Actually, no, he's talking about superchargers. My assumptions lead me to believe this was a joke and/or an attempt to increase your post count.

I've read a little about this before, but haven't really understood the differences very much and have wondered as well, so I decided to do some brief research on the topic since I have some time and interest.

5.0convert did give a great nutshell explanation, as daggar said

Here are some things I would like to add:
Roots blowers are called that because a couple guys w/ the last name of Roots invented them as an air conveyor for mine shafts. Later in the 1930's, GM used them on diesel motors - mainly to help w/ exhaust gases.

Roots and twin screw blowers offer more low-end torque because they don't have to spool up, so they're better for hauling and cars w/ a lack of low-end torque (generally smaller motors).

Seems to me that unless you plan on pulling things or are going to keep it belowe 3000rpm or so, you'd probably want a centrifugal - especially if you plan on racing; however, as with anything, everyone is differenent and different needs/variables may determine what's best for you.

If anything that I said is wrong or needs clarification, please someone do so. I never claimed to be a pro at this and really just read and tried to understand some of this tonight.

BTW, here are the sites I read a little at and they seemed to be good (at least a decent introduction to the topic):
http://sporttruck.com/techarticles/1436 - this one mentions chevy trucks, but the info. presented is basic and should still be the same
http://www.superchargersonline.com/faq.asp

 

[macx]

The isntant torque from any street rpm is one popular advantage of the roots and especially the screw type (Kenne Bell and Whipple, which is the screw type version of the Eaton roots type). The screw type with it's greater efficiency, less parasitic power loss, and lower heating of hte air charge versus the roots type doesn't fall off in the upper rpms nearly as much as the Eaton.

Matter of fact, Alternative Auto replaced the stock Eaton roots on a Mach 1 with a screw type Kenne Bell and gained I believe over 100 hp, with gains widening as the rpms climbed. I've also recently read articles about replacing the Eatons on the late model 4v Cobra mills with the Kenne Bell / Whipple type and with fuel system and ignition / ecu tweaking are getting something like 700 rwhp!