Centrifugal vs Positive Displacement SC
 

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:

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.

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.

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.

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.

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.

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.

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:

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

This is all well and good, but wouldn't a turbo be more efficient (work in<work out) than a centrifugal super charger? The way I see it, and I could be wrong, but a centri-SC is just a gear driven turbo, so you're using engine power to turn the compressor, instead of having exhaust gas do it. I'd imagine there's less boost lag with this type of SC, but you still either get a huge lump of power up top, or a lump of power in the middle then a loss of torque at the top end as the compressor airs out.

How is a centrifugal supercharger's boost output better than the linear output of a twin-screw (not roots)?

Turbo is the best of them all, hands down no question.

Best how?

To me the big trade off is the incredibly high heat turbos create. It may be more efficient, but there is always a trade off.

Well all the fastest cars out there aren't mostly turbo for a reason. They do make a lot of heat and are more complex than the others but those can both be managed very easily.

Nonsense. Look at the efficiency charts and factor in ~90% mechanical drive efficiency that they don't state, compare the pressure ratios and speeds, and tell me which one is better. The ability to make more boost is indeed based on the size of the blower though.

Actually that becomes close to inconsequential in some sense once the blower's speed gets high enough that its VE approaches maximum, if we're talking in relative terms. It will shove approximately the same amount of air into the cylinder across a wide range of engine speeds, so the torque becomes some kind of direct indication of other aspects of efficiency. On an NA engine the power is very sensitive to flow because not only does it affect pumping work, it directly influences the amount of air and fuel that is inducted.

As the blower's speed gets past a certain point the efficiency falls, the engine's efficiency drops off because of various effects (perhaps good evidence of this is the F20C's BSFC chart which is one of the only performance engine charts that can be found, efficiency goes to total shit above 8000rpm, indicating it's not just a matter of VE decreasing) but the blower's volumetric efficiency goes strictly up as its speed increases, which counteracts these effects to some degree. Of course if the flow is so bad that the pressure increases well past the blower's efficient operating level, then you'll lose some blower VE as well and lose power.

So the most efficient Eaton TVS unit is claimed to hit 76% thermal efficiency (sounds like mechanical efficiency of the drive isn't taken into account though, so minus a few percent), is that not coming close? While a bunch of supercharger companies don't even tell you anything about adiabatic efficiency, a bunch do... I suppose one could also point out the fact that the notably high efficiency "islands" are quite small on the TVS chargers, but still, they manage a very high peak efficiency. Better yet though, Eaton supposedly has some new designs that are even better coming through the pipeline soon.

I finally got an email from eaton and they claim ~95% mechanical efficiency on the smaller (up to 1320) TVS units and also told me that Mechanical efficiency was taken into account when making their performance maps. the high peak of 76% might be small but when i ran our cars data against the R1100 next gen TVS Map that was in the downsizing brochure and we get 74% thermal efficiency from 3000rpm to 6500 (70-72% below 3000) and 76% from 6500 to redline. i would say thats pretty good for Positive diplacement.

That new procharger looks great too but honestly i'd rather have the positive displacement to be able to move the weight as close to the firewall and as central as possible to minimize the effects of the extra weight (not that it is much at all relative to the car.)

The reason why turbos are used on cars aiming for top speed or high horsepower is because they can install a planet-sized turbo and use all the road or time in the world to finally get to full boost. For a daily-driver/autoX car, this is totally useless. Having all the power at the top 10% of the RPM band may be great for top speed, but if you need mid-range power in the middle of a corner, you're screwed.

So "best" is rather subjective.

The (slight) issue with this is that you automatically lose 10% drive efficiency or so from the CVT.

Having a CVT driven supercharger is certainly the "obvious" way to do it though.

Things would get really interesting when this is used with a turbine on the shaft as well, because this would allow you to spin the turbine up at low speed and improve its efficiency.

With individual, carefully matched Roots blowers piped to each pair of cylinders, and a rather wide ratio CVT, things can get really interesting too but I won't go into that.

The thing is, engines are turning more and more into mild hybrid types and OEMs are working on electric powered turbos (which solve basically all these problems), which are supposedly pretty close to arriving on the market...sure it's not tuner friendly but can you argue with efficiency and great response?

If you are going to try an argue that a centrifugal setup is better than a turbo then idk what to say lol

What? It's a fact that turbos (as they are now) have several severe shortcomings. What are you trying to argue?

So do centrifugals

Yes, but the drawbacks are different. So you can't directly compare.

You cant directly compare to means of forced induction? Pretty sure thats not true

Stop being difficult. All he said was "better" is subjective, and the obvious reasoning is that there are different criteria in which each method is better. And yes you can't directly compare because they have different attributes, each of which has a pretty clear winner.

Either way I think you'll have a badass machine at your disposal. I guess it all comes down to budget and goals but IN MY OPINION, I prefer and think turbo is better.

this is a great stepping stone for variable SCs but we need on the fly ratio changes. make no mistake, for an aftermarket product it is great. i just want to see OEMs start using something like this. IMO it would make the turbo obsolete...

perhaps Rotrak's version can be more efficient?

[ame="http://www.youtube.com/watch?v=ihdo78KsMOA"]Variable drive supercharger Rotrak (Part 2) - YouTube[/ame]


imo electric turbos are a myth. i'll believe it when i see it. more likely than not would be a performance hybrid system where the electric motor "assist" is used at low rpm while a powerful motor with large turbos spool up. that same motor can also be used at high speed as a KERS style boost. this is what i want to see...

no he didnt. u guys dense? he clearly said that turbos and cent SCs are good at different things so you cant really compare them.

Someone say electric supercharger...

https://sphotos-a.xx.fbcdn.net/hphot...86007063_n.jpg

I use my FR-S as a daily driver. I'm looking for a little more power. What is important is reliability with no engine issues. I'm not looking for huge HP. Somewhere between 250-300. Again ... reliability is the theme. Do I get the centrifugal or turbo?

Thanks

centrifugal would be your best bet. super easy on parts and should meet your power goals.

All mechanical CVTs inherently have some extra frictional losses since there is some sliding action going on due to a small variance in speeds. So I don't know how efficient the best CVTs are but it's not as good as the good ole discrete gears.

The thing stopping us from having electric turbos is the 12V system. You can't have high power density electric motors on 12V. That's why I think it's going to be a post-hybridization thing, as alternators and starters are ditched for flywheel mounted generators, belt driven accessories are ditched for electrically driven ones, and 12V is relegated to mundane things like switches, lights, etc., the infrastructure necessary to pipe the large amounts of electrical power that a supercharger would require would start to exist. At the end of the day efficiency would be perhaps the same as a CVT but it would become a modular electric component rather than a mechanical add on.

but why wouldnt you use whatever energy you generate to power a motor to directly drive the wheels? it makes no sense to use that energy to power an e-turbo instead of a motor. the germans with their single motor ZF hybrids are finding this out the hard way. their hybrids SUCK. toyota, ford, gm, and now honda are all aboard the 2 motor system. that's the future imo. not just for economy cars but sports cars as well. i keep thinking about a hybrid system like the one in the GS450h. that car gets 29/34/31 with a 4200 lbs car. i can only imagine what that system can do in a smaller, light weight car with a slightly larger, more energy dense li-ion battery...

Because investing that energy into moar air gives moar power. Same reason why you use the energy from the engine to power a supercharger, instead of the wheels.

I don't know about 2 motor system, for performance applications yes, but depending on the setup they could just ditch one and save the money (and lose some acceleration). Hybrid cars are already pushing it when it comes to affordability.

serialk11r is correct. Without a high voltage circuit in the vehicle, you need very large wires and lots of current to drive electric accessories (including electric-powered forced induction).