Roots Blower Vesus Centrifugal- Which Nets More HP?

[38flattie]

I've looked everywhere, and cannot find the info I need.

I've read several places that centrifugal superchargers make more net horsepower than roots type superchargers, because of the HP needed to turn the roots blower.

Yes, I understand the First Law of Thermodynamics- that's why I question this!

First off, is this true?

I'm trying to figure out approximately how much more horsepower my Procharger D1SC could make, than my stripped 6-71, at 14lbs boost.

Anyone know where to find this info, or have dyno comparison numbers to share?

[Dynoroom]

What you need but are not likely to get are the compressor maps for the units in question.

The basic answer is not as easy as a yes or no but if all else is the same, lbs/min air flow, pressure ratio, etc. the centrifugal blower wins.

Then we could talk high helix or even screw blowers but thats not what you asked about......

[38flattie]

Thanks Mike!

All things being equal, is the advantage of the centrifugal enough to warrant the change?

Since I'm looking for the most HP possible, please feel free to expand on the high helix or screw blowers , if there is an advantage to be had there.

[akk]

Garrett general catalogue is very informative. You will discover that temperature really affects the air density and how much oxygen actualy gets stuffed in the motor for a given amount of boost. Whipple and centrifugal are more efficient than roots and heat the air less and use less crank horsepower to turn. Good intercooling can make a huge difference! Of coarse turbo charging unloads the motor and can make more power. It takes hundreds of horsepower to drive the mechanical type of huffer and requires more boost to get the same power out.

Akk

[Dean Los Angeles]

I think the seat of the pants answer would always be the centrifugal blower because they spin easy by hand. The answer is never that easy.

And 14psi isn't the only comparison number. The flow rate at that pressure makes a huge difference. You would have to have a flow map of the Procharger and roots blower to see where you are in the curve. If you are in the middle of the curve on one and on the ragged edge of the other the comparison isn't valid.

I looked through the Procharger web site and they have zero technical information. The specification chart gives you little useful information. Makes you wonder.

[Cajun Kid]

I was on the phone with Jason from ProCharger yesterday.

N/A on C12 race gas my 255 cu in SBC "E" motor at 10 to 1 compression makes 480HP.  (my setup is 13.5 to 1 ) but for Blown I had to reduce to 10 to 1, they prefer 9 to 1)


At 10 to 1 with the D1SC and an air to air intercooler (using C16 race gas) and Blow Thru 4150 Carb at 8psi Boost I was told 55% HP Increase.
So the 480HP boosted would go to 744HP.
Does this sound correct ?

My calculations show I need 600 RWHP at Bonneville to do the spped I need.. so 700 motor HP would do the trick with a few HP to spare...

Charles

[Dynoroom]

Thanks Mike!

All things being equal, is the advantage of the centrifugal enough to warrant the change?

Since I'm looking for the most HP possible, please feel free to expand on the high helix or screw blowers , if there is an advantage to be had there.

You answered your own question. Yes it's worth it if your only looking for max hp.

But as it has been mentioned chargeair cooling, plumbing, drive assy type, ect. do indeed fit into the decision process.

for me the the rest of the subject (screw blowers etc) is much to time consuming right now, call me if you'd like.

[RichFox]

Lets start off by agreeing that I don't know anything about this. However, the centrifugal looks like a better deal. But because they are usually kind of small they must be spun very fast to produce boost. At Turlock swap meet i saw a guy trying to sell a newly overhauled B52 air cycle machine for $25 with the manual. Noe that has some nice sized compressors without being overly big. And very well made on a cost is no object platform. You have not been thinking inside the box much so far. Why not look into something like that?

[RansomT]

I was on the phone with Jason from ProCharger yesterday.

N/A on C12 race gas my 255 cu in SBC "E" motor at 10 to 1 compression makes 480HP.  (my setup is 13.5 to 1 ) but for Blown I had to reduce to 10 to 1, they prefer 9 to 1)


At 10 to 1 with the D1SC and an air to air intercooler (using C16 race gas) and Blow Thru 4150 Carb at 8psi Boost I was told 55% HP Increase.
So the 480HP boosted would go to 744HP.
Does this sound correct ?

My calculations show I need 600 RWHP at Bonneville to do the spped I need.. so 700 motor HP would do the trick with a few HP to spare...

Charles

Well, how can I put this …. No.   There are too many variables there and it just doesn’t sound right to me.  For one, lowering the compression (which I am going to assume you haven’t dyno’d your engine with 10:1 pistons and compared it with 13.5:1 pistons) changes the chamber size and quench area.  That could lower the HP more than just dropping compression 2.5:1 (which is probably good for 30-40 HP in itself).    Next, it takes HP to turn that blower.  My 3.0L Taurus uses up more than 50 wHP turning a Vortech T trim.  I know that figure by doing the entire math with the injectors.  And then you throw in the efficiency of the blower map.  Then if you want to get really complicated, your cam profile has a lot to do with how efficient the engine uses the additional air especially at higher RPMs.

If it was me, I would look at closer to 11-12 psi of boost and lower the CR to 9.5:1 … of course that’s a WAG especially since I don’t know the flow properties of your head and/or the dyno curve of the overall engine.

[WOODY@DDLLC]

Buddy, you thought it was a simple question right? As has been pretty much stated here it's not quite that simple! It also includes the 2nd law of thermodynamics! 

Rule of thumb: (0.00436 * PSI * CFM) / efficiency = HP to compress the air. So all things being equal (NOT) then efficiency is the short answer.

Roots 50%~55%, spiral ~68%, centrifugal ~69%, screw ~72% (Whipple claims higher!) and the odd duck Comprex ~84% 

http://www.modified.com/editors/0705_sccp_comprex_compressor_supercharger/index.html

Just when you thought you knew it was safe to get back on the salt!! 

[McRat]

I'm a "student" of turbo charging, ie - I'm constantly getting schooled  

Impellers compress the air, so perhaps some of this applies?

It depends on the "boost" you want to run.

Any type of advanced impeller turbo design is capable of running at better than 75% efficiency at Pressure Ratios over 3:1 (~30PSI manifold boost).  Here's the impeller map of what I ran in 2008:


Note that at roughly 45psi gauge boost, it's STILL at 75%.  That impeller still works excellent to 60psi boost.  

The higher the boost you want to run, the better "turbo" compression works.  Many centrifugal blowers on the market use fairly "old" impeller design though.  Latest stuff is a continuously changing angle of attack, in all three axis, and has a set of shorter blades to resist compressor stall and use a map enhancement groove.

But at up to 2:1 pressure ratio, IIRC, the positive displacement wins.  And that's why you're seeing a lot of OEM cars with factory positive displacement superchargers.  They only run 2:1 max (15psi).

[redhotracing]

At 10 to 1 with the D1SC and an air to air intercooler (using C16 race gas) and Blow Thru 4150 Carb at 8psi Boost I was told 55% HP Increase. So the 480HP boosted would go to 744HP. Does this sound correct ?

Charles

Well, how can I put this …. No.   There are too many variables there and it just doesn’t sound right to me.  For one, lowering the compression (which I am going to assume you haven’t dyno’d your engine with 10:1 pistons and compared it with 13.5:1 pistons) changes the chamber size and quench area.  That could lower the HP more than just dropping compression 2.5:1 (which is probably good for 30-40 HP in itself).    Next, it takes HP to turn that blower.  My 3.0L Taurus uses up more than 50 wHP turning a Vortech T trim.  I know that figure by doing the entire math with the injectors.  And then you throw in the efficiency of the blower map.  Then if you want to get really complicated, your cam profile has a lot to do with how efficient the engine uses the additional air especially at higher RPMs.

If it was me, I would look at closer to 11-12 psi of boost and lower the CR to 9.5:1 … of course that’s a WAG especially since I don’t know the flow properties of your head and/or the dyno curve of the overall engine.

I have to agree with T on this one... IIRC, The your E motor is a de-stroked 18* headed motor... built for high CR and high RPM's... Lowering down to 10:1 and adding a centrifugal supercharger may net you 700hp at 8000K+, but you're going to be giving up power elsewhere. If you were running a big single (88mm+) or twin turbocharged setup (61mm-ish) with an air to water intercooler and maybe a progressive N2O hit to help spool the turbo(s) you'd be losing the parasitic draw on the motor and picking up HP across the
powerband. You could make big power either way, it just depends how much boost, where you're gaining, where you're losing... IMHO

[38flattie]

Thanks guys- lots to think about here.

The intake and intercooler will remain, irregardless if the supercharger used.

Rich, isn't the air in an Air Cycle Machine compressed by a centrifugal pump? Dad was an airline mechanic, and ACM's were part of the planes systems, so I'll explore this idea with him tonight!

Buddy, you thought it was a simple question right? As has been pretty much stated here it's not quite that simple! It also includes the 2nd law of thermodynamics!  

Rule of thumb: (0.00436 * PSI * CFM) / efficiency = HP to compress the air. So all things being equal (NOT) then efficiency is the short answer.

Roots 50%~55%, spiral ~68%, centrifugal ~69%, screw ~72% (Whipple claims higher!) and the odd duck Comprex ~84%  

http://www.modified.com/editors/0705_sccp_comprex_compressor_supercharger/index.html

Just when you thought you knew it was safe to get back on the salt!!  

Woody, it appears there isn't any, or at least I can't find any, empirical data on the HP it takes for each style of blower to make the needed boost.

You're equation, along with the efficiencies, may be as good as I have to work with.

As for the second law-that's why I have the intercooler!

That being said, it looks like the screw compressor wins out, followed by the centrifugal. I wonder though, how much efficiency is added by the teflon stripping in my huffer?

I have the Procharger D1SC, and don't own a screw type, so I'll probably play around with it this winter, to see if I can get any gains out of it.

[RichFox]

They take bleed air and use it to drive the turbine section which is connected to the compressor and the same size. Air exhaustest out of the turbine side and feeds into the compressor to be recompressed. Seems like it wouldn't work. But I am led to believe that it results in cooler compressed air.

[jdincau]

http://en.wikipedia.org/wiki/Air_cycle_machine