Roots Blower Vesus Centrifugal-Which Nets More HP?

I didn't realise that would put you in a diffrerent class... Sorry.

I'd still would seriously look into a two stage setup.
( Roots & Centrifugal)

You are already running the Roots, right?

So you are already almost half way there...

 

I was there the year they had the 14-71 on it. Someone came up to them with a picture of the car at speed--that blower had so much aero drag on it, it was lifting the nose of the car up... it looked like a gasser.
They didn't have any cowling or covering over that blower--just had it sticking out the hood for God and All to see, and it was acting like a parachute.

-Brad

 

If you look at promod racing, then you'll see that almost all of the fastest cars run blown alcohol setups with PSI screw blowers. They can move vastly greater amounts of air compared to a centrifugal. The alcohol negates the heat gain.

Morris has made 2,500 hp with an F3-R Procharger, however, a PSI screw can make twice that. Like you said, the screw blowers aren't really roots systems, though.

 

"Can't I use pulleys to 'gear' the centrifugal to produce the boost I want at 5500 RPM, and therefore get away from power loss because of excess blow-off? More HP at max RPM is exactly what I'm looking for- I think!"

Yes but McCulloch had an even more sophisticated way of doing things. They had a variable speed drive with an adjustable pulley like a snowmobile drive.

The outside half of the pulley on the blower could move in and out, effectively becoming larger or smaller, controlled by an air cylinder inside the blower. Essentially it had 3 modes of operation.

1) Driving down the road at part throttle. In this mode the pulley was large, it drove the supercharger slowly and provided no boost. Air passed through the blower to the engine but the supercharger was "idling".

2) Punch the gas pedal to the floor. This activates a solenoid in the blower, by way of a kickdown switch on the gas pedal. Blower goes to full boost.

3) Supercharger pressure goes above a preset level (usually 4 or 5 pounds) and the pressure backs off the pulley, reducing blower speed and holding boost to the desired pressure.

Net result. No wasted power when the blower is not needed. Full power when it is needed even at lower RPMs. But no danger of overboosting as speed builds up.

This system worked OK up to a point. Eventually they decided it was unnecessary and eliminated it around 1961, or about 8 years after they first used it.

 

Yeah, I don't watch promod much, just the streetcar shootouts because several buddys compete. One is a nitrous car the other centrifigal so I was just trying to stick with what I personally am familiar with.

Similar to what I said with top alcohol funnys and dragsters, I just forgot to also include pro mod in that.


Scot

 

I have a McCulloch Vs57 on my Roadster.

Accelerating through the gears, the variable speed thing lagged so far behind the engine RPM it was pretty much useless.

On its current rebuild, I had the variable speed part removed and the blower is now built to the later non variable speed spec.

 

800 hp 121 cubic inch 4 cylinder turbo charged race cars...that's 6 and 1/2 hp per cubic inch and these are not short duration drag engines.
WW2 aircraft engine designers used to say this about centrifugal supercharging,either mechanical or exhaust driven, "If mechanical strength is adequate,the only limit to power is detonation."

 

I'm trying to figure out approximately how much more horsepower my ProchargerD1SCcouldmake, than my stripped 6-71, at 14lbs boost.

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

On your given engine & all other things equal, 14lbs of ambient temp boost from any source should be the same HP. The difference will be parasitic loss of centrifugal vs roots type, the effectiveness of air to air intercooler vs air to water intercooler.

The intercooler will most likely be where your biggest gains will be found providing the 14 psi remains. The air to air will be virtually unlimited on its cooling capability. That's purely a thought experiment based on some OT stuff.

The ice water fed air to water intercooler just doesn't have the surface area or the contact time to cool off the boost. Much better than nothing but I see the air to air doing a better job of it. 14 psi of heated air doesnt contain as much oxygen as 14 psi of cold air.

 

From what I see Screw Blowers seem to be the most efficient for blowers.

As for Fastest Street Car Shootouts, many of the serious boys these days are most certainly using Turbos. And until someone outruns Larry Larsen's twin turbo Nova and it's 6 second passes during drag week I'll stick with that statement. And it will probably be a Turbo car that takes him down.

 

The downfall of a Roots blower is pumping losses. The rotors move air at atmospheric pressure and push it into a manifold that is above atm. pressure. When the rotor chamber opens to the manifold, the pressurized manifold air rushes back into the chamber, reducing overall pressure until the rotor pushes it back into the manifold again. This pulsing pressure wastes power and produces heat. The higher the manifold pressure, the greater the losses. It's like blowing up a balloon and allowing half of each breath back into your lungs. Helical rotors open the chambers to the manifold more gradually, reducing the pulsing effect. Screw type rotors have internal compression which reduces the pulsing further.

It's like that hall closet with too much crap in it. You open the door to put something in, and 10 things fall out. Roots supercharger opens the door, lets it all fall out, adds the extra to the pile, then shoves the whole mess back in. A centrifugal cracks the door, whips the extra in, and slams it shut before anything can move.

 

I agree on the turbo thing. A lot of the problems facing turbo guys and spooling, lagging etc. have been solved in the last few years. I just like to be there in person when they hit the trans brake and spool up. It's just insane the racket they make. Almost as good as your eyeballs wiggling in your head from top fuelers.


Scot

 

The missing factors in that quote are; the heat tolerance of critical parts, and the ability of the cooling system to get rid of heat.

 

Have you been around any really nice and larger w/a coolers? I have a buddy with a ot vehicle and ut has a large turbonetics w/a and a ice water tank and it will bring the charge air temps below freezing with a bit of salt in the mixture of water and ice. This is at 150home psi boost and a compound setup. W/a coolers are very impressive

 

I have two friends who run ProCharger set up in their rides. after getting a ride in them, I am sold on them.

 

I work with a guy who tuns an 07 GTO in "Pro Street" class. They are the quickest small block door car in history at 5.91, and the Fastest small block drag car of any kind at 2447 and change. All this with a 396" SMALL BLOCK ~ that is what turbos will do for you ~ 3000 HP !!!!
And yeah, when it gets up on the two step the noise it makes is incredible, no Trans Brake here, it a Lenco with a Crower Clutch car

 

I am certainly glad I am not the only one that has noticed that. I've tried telling people about it and they look at me like I'm nuts.

 

I like turbos, but not for this application. They would move me from Vintage class to Modified class, so they are not an option.

 

No, my exposure has been Only to the smaller A/W units that fit under the blowers and only large and larger A/A used in turbo applications. One of those larger W/A ones that you speak of and a centrifugal should out perform the 6-71 on the top end.

 

The amount of air that is cooled is proportional to the surface area of the i/c core. I have an OT drag car that runs a Morris 372 SBC with an F1 and A/W. The cooler's core is large enough to support well over 3,000 CFM. My F1 only pushes 1,500 cfm at 70,000 RPM impeller speed.

The good thing about an A/W cooler is that you can get below ambient on hot days. There are some days when we're over 100* ambient plus underhood temps. My A/W can get the intake charge under 60* with ice. Depending on the efficiency of the i/c, you may lose up to .5# of boost, but you can more than make up for it with more aggressive timing.

For size reference, the ducting is 4".

 

Ahem, Blowers(generic) don't generate heat other than from whatever friction there is. They condense the heat that is there. When you put two cubic feet of air into one cubic feet of space, you increase the pressure by one atmosphere, and whatever heat is in the original volumn is now in a smaller volume. No heat is generated. It was there all the time.

 

In a perfect world what you say would be true. But, inefficiency also produces heat.

 

And your point is?

 

The point is.. that physics always rules. Arguing over roots(positive displacement) vs centrifugal and the heat they "generate" is moot. The stories are based on emotion, like Ford vs Chevy vs Dodge. Regardless of the way the air is compressed the laws of Physics are the same. Like most mechanical things, energy in = energy out minus drag. The heat from friction would be minor compared to the concentrated heat of ambient air being compressed. Efficiency would vary linearly with the differing values of this friction resistance. Modern centrifugal blowers have come into their own by using high tech low resistance bearings that allow very high turbine speeds. It still takes power to turn them, but friction drag is much reduced.
The summary is... roots or centrifugal superchargers do not generate differing amounts of heat,all other thigs being equal. If you didn't rear the entire thread, you have no idea..

 

One thing i do know, is that if you pack twice as much air into a cylinder you'd better have twice as much fuel, in order to maintain an acceptable Air/Fuel Ratio. Parasitic losses are less with centrifugals but the ultimate blowers aside from turbos (which make crazy power) are the screw blowers, which essentially build pressure in the blower housing and discharge the air into a lower pressure area (the manifold), thus cooling the air and increasing efficiency (burning more fuel) Check out Whipple's and SSI'S websites for more info.

 

Here's are Eaton's m122(2000 cc) roots style vs. tvs1900 which has a pressure ratio of 2.4. Here's a good comparison. At low pressure the roots wins for volumetric efficiency, at higher the tvs. tvs wins in temperature in both. Other charts say m112 is 50 HP at 10 PSI, 1900 is 35 HP.
http://www.smokinvette.com/corvette/articles/eaton-tvs-supercharger/

 

You are not seeing the entire picture. Friction of any kind, bearing or otherwise, is nill in both Rootes and centrifugal blowers. Compressing air results in a heat increase, but that's not the end of the story. The less efficient the unit, the more it the air is heated. Inefficiency produces heat. Look at a flow map of cyntrifugal compressor. Typically piloted are pressure, volume, and efficiency. The further you get from the highest efficiency island on the flow map, the more the compressor will heat the air the air. That's a key factor in matching compressor style/design and size to a given application, and why different styles/types and sizes of compressors are made.

 

And to ad to what Al says above from supercharger engineers;Rootes superchargers don't compress air like a centrifugal.Rootes moves air and it becomes pressure when it backs up in the intake.

 

When I was in high school the closest strip was over an hour away so only a couple of my friend had seen top fuelers. I used to love to take the ones that had never seen them to the track and watch the reaction when the first one made a full pass.

One of my friends wasn't really a car guy and he about pissed himself when the first one left the line. I laughed so hard I fell on the ground. The look on his face of fear and disbelife was just priceless.

All I said was "Jim I tried to tell ya, it's like a fully automatic 12 gauge running 300 rounds per minute".

He just kept saying "I felt like I was having a heart attack"

 

http://industrialairblower.com/categories/NSR(Normal)_50_three_lobe_Roots_blower-en.html

The performance tables give the model, bore,r.p.m.,discharge pressure, air capacity and required power of the blower.

1)The air capacity in the tables is indicated in the standard suction state,The standard suction state herein mentioned is defined as the condition at 20℃ temperature, 1.0332kgf/cm2 (101.3kPa) absolute pressure and 65% relative humidity.

2)The reference air capacity ( 0℃ temperature and 1.0332kgf/cm2 (101.3kPa) absolute pressure) is gencrally indicated in Nm3/min However,it may be converted into the standard air capacity by the following equation, if the suction pressure is equal.

Qs=QN x1.0332

Qs:standard air capacity

QN:reference air capacity

3)The discharge air capacity can be converted into the standard air capacity by the following equation.

Qs=

Qd: discharge air capacity, in m3/min;

Pd: discharge pressure,in kgf/m2:

ts: suction temperature,in ℃ ;

td: discharge temperature,in ℃.

4)According to the air capacity and discharge pressure as calculated above, the model number, bore, r.p.m.and required power can be found in the performance table.

5)The motor powers are indicated by color marking, and the motor powers to be used should be that indicated.

6)The choice is overlapped depending upon the type of blower. For reference, however, selection should be lower number blowers for the economy and higher number blowers for the sound level.