Centrifugal vs Positive Displacement SC

[RedLeader]

Originally Posted by 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

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)?

[Tansey86]

Originally Posted by RedLeader

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.

[wootwoot]

Originally Posted by Tansey86

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.

[Tansey86]

Originally Posted by wootwoot

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.

[serialk11r]

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.

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.

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.

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.

Originally Posted by 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.

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.

[unijabnx2000]

http://www.lsxtv.com/news/procharger...-supercharger/

[FreshFRS]

Originally Posted by serialk11r

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.


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.)

[RedLeader]

Originally Posted by Tansey86

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.

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.

[serialk11r]

Originally Posted by unijabnx2000

http://www.lsxtv.com/news/procharger...-supercharger/

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?

[Tansey86]

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

[serialk11r]

Originally Posted by Tansey86

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?

[Tansey86]

Originally Posted by serialk11r

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

So do centrifugals

[serialk11r]

Originally Posted by Tansey86

So do centrifugals

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

[Tansey86]

Originally Posted by serialk11r

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