Landracing Forum
Tech Information => Technical Discussion => Topic started by: 38flattie on February 02, 2012, 08:11:29 AM
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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! :-D
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?
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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......
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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.
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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
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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.
(http://tomhenryracing.com/THRSS/supersidebarimages/725.35.gif)
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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
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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.
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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?
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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.
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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! :-D
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% :-o
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!! :cheers:
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I'm a "student" of turbo charging, ie - I'm constantly getting schooled :oops:
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:
(http://www.turbobygarrett.com/turbobygarrett/sites/default/files/default_images/turbogroup/performance_maps/GTX4202R-Compressor-Map.jpg)
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).
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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
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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! :-D
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% :-o
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!! :cheers:
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! :-D
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.
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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.
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http://en.wikipedia.org/wiki/Air_cycle_machine
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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
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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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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
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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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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
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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.