Author Topic: Roots Blower Vesus Centrifugal- Which Nets More HP?  (Read 20154 times)

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Offline jl222

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Re: Roots Blower Vesus Centrifugal- Which Nets More HP?
« Reply #15 on: February 02, 2012, 05:48:16 PM »
  20 yrs ago a friend was able to inter the formula for adiabatic compression [at out side temp and 14.7 psi which numbers could be changed] in my computer and from there we made up a program which had the ideal temp rise or 100% efficiency --45%--65% and 75% across top of page  and boost pressure from 2--100 psi
down left side. This was done in Lotus [sp] saved program but doesn't work in my current computer but I printed
out results and saved some.

  This formula I got from the book Turbocharging by Huge Macinnes
  Roots blowers were listed at 45%-50% efficient tubos and centrifugal 65 --75%

  Print out at 70 deg day 14.7 psi atmosphere at 14 lbs boost shows 315.51 at 45% efficiency--239.97 at 65%
and 217.31 at 75%

  This print out is more like Bville with less atm psi at 12.7psi and 70 deg day [ well 70 in the morning ] :-)

  14 lbs boost 345.64 at 45%   260.83 at 65% and 235.38 at 75%

  These temps are just compressed air adding fuel or gas not figured, in but alcohol and nitro added to roots blowers makes them work from the laten heat of evaporation.

   The colder the air the higher the density and results in more mass of air in engine and vice versa with hotter air.

  This is why we use Procharger superchargers :-D And they do have the latest designs.

  Also with the Procharger you can run a larger intercooler.

  


              JL222

Offline 38flattie

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Re: Roots Blower Vesus Centrifugal- Which Nets More HP?
« Reply #16 on: February 02, 2012, 10:33:56 PM »
You have not been thinking inside the box much so far. Why not look into something like that?


Rich, if you knew how far out of the box I get sometimes, you'd quit associating with me! :evil:


jl222, that's great info. I never thought about how the efficiency would effect the air temp, and therefore the HP.

The lower temps of the centrifugal make it look more attractive than before!

Thanks again!
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Offline jl222

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Re: Roots Blower Vesus Centrifugal- Which Nets More HP?
« Reply #17 on: February 02, 2012, 11:23:54 PM »
You have not been thinking inside the box much so far. Why not look into something like that?


Rich, if you knew how far out of the box I get sometimes, you'd quit associating with me! :evil:


jl222, that's great info. I never thought about how the efficiency would effect the air temp, and therefore the HP.

The lower temps of the centrifugal make it look more attractive than before!

Thanks again!

   The efficiency in supercharging and in the tubo maps that are available is the temp. But it also takes hp to make heat


  I was lucky to come across this book ''Chemical Principles by Selwood'' with a formula for gas volume

  Charles law    Volume 2 =Volume 1 x temp 2 divided temp 1

  Book also has charts which make it easier to understand .

  Effect of temp on 1 atm of hydrogen  300 deg k = 578 ml volume
                                                     610    =      1180 ml volume
 
  Its the same air, the volume has gone up but its half as dense from 300 to 600 but twice as dense from 600 to 300

   So as air is heated you get expanded air but as its cooled you get shrunken denser air,to pack in cylinders and go off, thats what we want.

  All the gas laws are in the 1st chapters of this text book.

                     JL222

                       

Offline desotoman

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Re: Roots Blower Vesus Centrifugal- Which Nets More HP?
« Reply #18 on: February 03, 2012, 01:28:17 AM »

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


Buddy,

YMMV, but this is just an example using a computer program.

I took the liberty of putting some numbers together for you and here is what I came out with. Assuming your ports flow 200 cfm, and the blowers put out 14 lbs of boost, and both have cold water to air inter-coolers, and everything else is the same.

The Centrifugal blower I used was a Vortech V4 Z trim.
The Roots was a competition 6-71.

Centrifugal at 6500 RPM, would make 686 HP and 554 TQ, but this blower suffers from not putting out much torque at low RPM's.

Roots at 6500 RPM would make 659 HP and 532 TQ, but this blower puts out goobs of Torque at low RPM's having a peak at 5000 RPM of 585 TQ.

IMO Roots blowers are fine for low boost levels say 14 lbs and below especially with a inter-cooler, but above that boost, the Centrifugal and Screw blowers really shine. I left turbo's out because they are not mechanically driven.

Tom G.
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Offline hotrod

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Re: Roots Blower Vesus Centrifugal- Which Nets More HP?
« Reply #19 on: February 03, 2012, 02:14:25 AM »
If you can find specs for your blowers and your heads will allow the engine to process the air available you can get a ball park guess (all else being equal) based on the amount of air each blower will flow at a given boost.

There are several different rating systems used by different blower and turbo/centrifugal manufactures.
The following assume that intake air temps reasonable and these are the inlet flow numbers before the blower heats the air.


Conversions

1 HP    approx equals   1.45 CFM
1 CFM   approx equals   0.0745 lb of air/min
0.108 Lb/min  approx equals 1 hp
1 Meter cubed/sec   =   35.314 CFS  = 2118.867 CFM
1 KG/sec = 132 lbs/min  approx equals 1771.812 CFM



Power varies approximately at the inverse square root of the intake charge temperature in absolute degrees for equal manifold pressures.
If temp is measured in centigrade add 273 to your thermometer reading to get absolute intake air temp.
If temp is measured in Fahrenheit add 460 to your thermometer reading to get absolute intake air temp.

If air temp in the manifold with blower A is 355 deg F and with blower B is 280 deg F and both are at the same manifold pressure, the ratio between the engines power output would be:

(355 + 460) = 815 deg F absolute
(280 + 460) = 740 deg F absolute

815/740 = 1.10135

square root of 1.10135 = 1.04945  -----> the cooler blower would make about 5 % more power all else being equal (ie same boost, heads could move the air etc.)

If manifold air temperatures are equal (ie using an air/water intercooler to get to the same air temp), then power varies directly with manifold pressure (assuming the engine can use the air flow, does not run into detonation etc.)

Larry
« Last Edit: February 03, 2012, 02:17:45 AM by hotrod »

Offline 38flattie

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Re: Roots Blower Vesus Centrifugal- Which Nets More HP?
« Reply #20 on: February 03, 2012, 06:24:47 AM »
jl222, Tom, Larry- thanks! :cheers:

Tom, you and Larry both come up with similar percentages, with Larry using jl222's temp numbers.

Right now, I'm not planning on any more than 5500 rpm, due to piston speed, and the fact that most flatheads are done making HP by then. The low end torque from the roots blower will definitely help us power through the high gears.

With the right pulleys, I should be able to get the centrifugal to produce max hp at 5500, correct? I would think it would be more manageable-i.e. drivable, as far as tire spin at shifts, but wonder if we can power through as high of gearing?

At some point, 5% more horsepower will be hard to come by, and this looks like the 'easiest way to get it. In addition to the HP increase, I can get it all under the hood, and round another corner off of this 'brick'!

I'm going to play with it this winter, as see what results I get.
With sufficient thrust, pigs fly just fine. However, this is not necessarily a good idea. It is hard to be sure where they are going to land, and it could be dangerous sitting under them as they fly overhead. -- RFC 1925

You can't make a race horse out of a pig. But if you work hard enough at it you can make a mighty fast pig. - Bob Akin

http://www.flatcadracing.org/
http://youtu.be/89rVb497_4c