Centrifugal vs Positive Displacement SC

[EN2_Squirrel]

I am sorry if this has been answered, but what is the difference between Centrifugal vs Positive Displacement superchargers(if any)?

[uspspro]

http://www.superchargersonline.com/i...age=page&id=35

[FreshFRS]

Originally Posted by EN2_Squirrel

I am sorry if this has been answered, but what is the difference between Centrifugal vs Positive Displacement superchargers(if any)?

instant boost response. centrifugal superchargers make max boost at the redline, and great for peak horsepower. PD superchargers in general will make 90% boost in about a half second, delivering a great midrange boost, torque and extremely linear power at the expense of a few horsepower up top depending on the size and efficiency of the blower. Eaton TVS its the only way to go to match a turbo's thermal efficiency (TVS up to 76%). :happy0180:

[Tansey86]

Centrifugal is a belt driven turbo essentially. It builds boost with RPM's and hits max at redline, it makes less torque than any other means of FI for the most part. More noisy at idle and less noisy at WOT, minus the BOV.

Positive displacement is a supercharger that directly replaces the intake manifold and feeds air directly to the engine that way. It is quiet at idle and " whiney " at WOT. Instant torque and HP grows gradually.

An eaton is a roots style blower and if you went positive displacement I would advise against a roots and go twin screw(ie whipple) as they are much more efficient and make better power.

[FreshFRS]

Originally Posted by Tansey86

An eaton is a roots style blower and if you went positive displacement I would advise against a roots and go twin screw(ie whipple) as they are much more efficient and make better power.

Eaton TVS generates less heat than a twin-screw and can generate more boost due to the higher pressure ratio.

[Tansey86]

Originally Posted by FreshFRS

Eaton TVS generates less heat than a twin-screw and can generate more boost due to the higher pressure ratio.

The ability to make more boost is based on the size of the blower, im sure a TVS will work fine but from what ive heard people say twin screw is better than roots.

[FreshFRS]

Originally Posted by Tansey86

The ability to make more boost is based on the size of the blower, im sure a TVS will work fine but from what ive heard people say twin screw is better than roots.

a higher pressure ratio allows a smaller blower to produce more airflow without generating as much heat. an R900 TVS will flow more air than the sprintex used in innovate's kit despite being slightly smaller, .9L vs .94L and will have 72+% thermal efficiency vs. about 65% for the sprintex.

[subatoy]

I take the sound of performance parts as a VERY important feature when i purchase anything. simply because I enjoy a good sounding car.

The whining sound of a twin screw SC is probably one of the most rewarding sounds to me. Appart from it's power delivery I love the clean simple package this SC creates. less parts and easy installation should translate to less $ too.

[roddy]

Originally Posted by Tansey86

The ability to make more boost is based on the size of the blower, im sure a TVS will work fine but from what ive heard people say twin screw is better than roots.

Better is subjective, but yes, the twin screw is more efficient than the old 3 lobe Eaton M and MP blowers. The Eaton TVS series is a newer design with 4 lobes that have considerably more twist. It is much more efficient than the old Eatons.

[so26]

I wonder if a positive displacement type sc would reduce the torque dip issue. I believe the hks centrifugal sc still suffered from it.

[Tansey86]

Originally Posted by so26

I wonder if a positive displacement type sc would reduce the torque dip issue. I believe the hks centrifugal sc still suffered from it.

It would make whatever torque from 2k until readline. Flat all the way across.

[uspspro]

Originally Posted by Tansey86

It would make whatever boost from 2k until readline. Flat all the way across.

Fixed.

Not exactly flat torque. The setup still has to deal with the VE of the head and exhaust/intake manifold at various RPM.

For example the roots blower on the mk1 MR2 SC would make somewhere between 8-14 psi (depending on which pulley), and make the same boost from 2000rpm to redline, but since the 4AGZE had weak ass stock cams the torque curve would fall flat on it's face after 6000 rpm.

[FreshFRS]

Originally Posted by uspspro

Fixed.

Not exactly flat torque. The setup still has to deal with the VE of the head and exhaust/intake manifold at various RPM.

For example the roots blower on the mk1 MR2 SC would make somewhere between 8-14 psi (depending on which pulley), and make the same boost from 2000rpm to redline, but since the 4AGZE had weak ass stock cams the torque curve would fall flat on it's face after 6000 rpm.

true story. our cams should allow for peak torque about 6000 with a roots blower, should fill in the torque dip and lose the lump at 4500. torque shouldn't fall off very fast as long as our ecu doesn't go pig rich above 6000 and cut timing. tuning can fix that though.:happy0180:

[Brian@Vortech]

There is some good information, but also a lot of incorrect data being given here. There are no pd blowers that even come close to approaching the adiabatic efficiency of a centrifugal supercharger such as a Vortech. We have compressors that exceed 78% adiabatic efficiency. Adiabatic efficiency refers to the amount of heat generated by the amount of work done (i.e. air being compressed). When a lot of pd companies use the term "efficiency", they are referring to volumetric efficiency. The term volumetric efficiency only refers to how well the chambers are being filled and has little to do with how well the supercharger is working. Do your research, don't be misled by word trickery and hype.

Also, you may want to read this - About Roots Type Superchargers