1471 boost

[g935]

How does 14lbs. of manifold boost from a 1471 compare to the same boost put out by an 871? Will the volume of the larger blower at the same boost be any different power wise than a smaller blower? I understand that the temperature of the charged air might be different if the 871 has to spin faster, but what if that were equal?
Geoff

[HEAVYBOAT]

I don't think I'm answering your question satisfactorily unless you're after the fact that the larger blower doesn't have to take as much HP from the engine as the smaller one. The smaller blower has to be overdriven quite a bit more to create the same boost and then overdriven even more than that due make up for the lost power due to the charge temp.
.
Rio
Rio, only other thing I think is missing here, is the parasitic losses from the weight of the heavier 14's rotors.

[rayson]

So if you have a 21 daytona eliminator with a 572 blown 871 lee inner cooler 7 lbs of boost,and you put on a 1471 and take the eight of with the same boost 7 lbs would the boat go slower because the 1471 is alot heavyer?

[g935]

I would think that the volume of air from a 1471 creating 14% boost would be greater than a smaller blower at the same boost. Pressure would be the same but the volume of air from the larger blower would be greater, thus creating more power. I'm thinking that the volume of air makes the difference. Or is it that you are spinning the blower slower creating the same boost the only difference?
Geoff

[Schiada76]

Boost on a roots is built in the cylinder and intake, wouldn't the pressure reamain constant as a function of volume?

[DetroitJim]

Lots of confusion here. First, 14 lbs. of "boost" doesn't mean a thing. Rootes blowers are very inefficient, less than 50%. The faster you spin them and the more resistance they encounter, what you get is heat. This causes thermal expansion and less dense air, the exact opposite of what we want. The pressure reading is mostly expanded air. Sending this heated air through an intercooler is needed to reduce the temp, but this is a band-aid. The larger blower will turn much slower and produce far less heat. Longer rotors don't take hardly any more power to spin, resistance to airflow does. Anything that increases air flow through the valves and exhaust will make more power, and lower the pressure.
So, back to your question, an equivalent volume of air from a bigger blower turning slower, will make more power (air density= more oxygen) and show a lower boost reading!
DJ

[Murray PE 857]

What about the difference in volume of air being moved by a smaller pump compared to a larger one. Maybe both X# boost pressure but difference in volume moved???

[DetroitJim]

Volume and density are two different things. A Rootes blower moves a fixed volume of air at a given speed. There is no centrifugal effect with higher rpm. Just the opposite, the blower literally squeezes the air out from between the lobes. This creates "friction" between air molecules. Unfortunately, all gasses expand when they encounter heat. This expanded volume contains less oxygen.The only way to make more power is to burn more fuel by adding more oxygen to the cylinder. A blower does do this, but in a very inefficient way. The faster it turns the more inefficient it is.

[g935]

Very interesting, thanks D.Jim
Geoff

[HEAVYBOAT]

I think you are correct HEAVYBOAT I was just to tired to try and focus on any more. (BTW- how you been?)
Ya, I was just following your lead with your good explanation. The weight of the 14 is a small variable, but it is one.
How have I been? real good thanks.....I’m still a blower guy, went from Blown gas intercooled, with nitrous and alky injection to straight Blown alcohol this year. Only got in a few test hits with it before the season ended, but I'll be out testing again in the spring.
When my buddies are building new combo's, I’ve been convincing them to try more efficient power adders, like Prochargers and turbo's while I keep beating myself up with the old technology!! Doesn’t make sense that I keep buying new Roots blowers, but I have gave it lots of thought, and my heart is still with the roots. The looks and the sound (especially blown alky) seals the deal for me.
Heres some new updated pics of my combo.
http://www.supermotors.net/getfile/562190/fullsize/img_0254.jpg
http://www.supermotors.net/getfile/562197/fullsize/img_0298.jpg
http://www.supermotors.net/getfile/562198/fullsize/img_0299.jpg
http://www.supermotors.net/getfile/562194/fullsize/img_0264.jpg

[DetroitJim]

Detroit Jim please note-> I pulled these out of a couple of posts and it just appears to me that some of these peeps don't understand the difference between "%" and "lbs", and where these terms are appropriate.
"1471 creating 14% boost"
"14 lbs. of "boost" doesn't mean a thing. Rootes blowers are very inefficient, less than 50%."
Maybe you could give an explanation as to boost, overdrive and underdrive
Rio
The 14% boost statement I assumed was a typo. As far as boost vs. blower speed, this could get really complicated! The true answer involves the kinetic theory of gases, laws of thermodynamics, the ideal gas law, and so on.
Simple answer:
A Rootes blower moves air. Period. Put it on top of an engine (another air pump) of a given size, driven by the crankshaft. If the blower produces less air than the engine can pump, you get vacuum. Spin it faster or make it bigger, move more air and you get pressure. This is fairly constant at wide open throttle regardless of RPM. When you see a higher boost reading as rpm goes up, it is HEAT, not more power.
Somewhat more complicated answer:
The faster a blower turns, the more heat it puts into the air. The air expands from heat, which creates pressure. The measurement of heat created vs. actual air density created is adiabatic efficiency. Around 40% to 60% for a blower. Centrifugals and turbos are much more efficient, they create boost by literally "throwing" the air molecules forward to impart velocity. The only real advantage of a rootes is that it moves air at low rpm as soon as the throttles are opened. That's what wins a drag race.
Even more complicated answer:
The kinetic theory of gases explains how individual molecules in a gas act and their relation to pressure, volume, and temperature.
This law has the following important consequences:
If temperature and pressure are kept constant, then the volume of the gas is directly proportional to the number of molecules of gas.
If the temperature and volume remain constant, then the pressure of the gas changes is directly proportional to the number of molecules of gas present.
If the number of gas molecules and the temperature remain constant, then the pressure is inversely proportional to the volume.
If the temperature changes and the number of gas molecules are kept constant, then either pressure or volume (or both) will change in direct proportion to the temperature.
Okay I'm going to quit now.:sleeping: :sleeping: :sleeping:
DJ

[paradigm shift]

Simple answer:[/B]
A Rootes blower moves air. Period. Put it on top of an engine (another air pump) of a given size, driven by the crankshaft. If the blower produces less air than the engine can pump, you get vacuum. Spin it faster or make it bigger, move more air and you get pressure. This is fairly constant at wide open throttle regardless of RPM. When you see a higher boost reading as rpm goes up, it is HEAT, not more power.
DJ
I am wondering how much does over or under drive fit in with higer boost as rpm goes up stated. I agree with the heat I am just trying to get my mind around how drive ratios fit in with it. We are talking fixed displacemnt (volume) in the blower vs engine cubic inches correct? So no matter what percentage under or over drive the boost stays the same through out rpm range say from 3000 to 6000 rpm at WOT. Just to throw out some numbers say 6% under drive might be 4lbs where 6% over might be 9lbs from 3000 to 6000 rpm.
Things that make you go hum??? :idea: You guys are selling me on the intercooler more and more even on low boost.

[DetroitJim]

Simple answer:[/B]
A Rootes blower moves air. Period. Put it on top of an engine (another air pump) of a given size, driven by the crankshaft. If the blower produces less air than the engine can pump, you get vacuum. Spin it faster or make it bigger, move more air and you get pressure. This is fairly constant at wide open throttle regardless of RPM. When you see a higher boost reading as rpm goes up, it is HEAT, not more power.
DJ
I am wondering how much does over or under drive fit in with higer boost as rpm goes up stated. I agree with the heat I am just trying to get my mind around how drive ratios fit in with it. We are talking fixed displacemnt (volume) in the blower vs engine cubic inches correct? So no matter what percentage under or over drive the boost stays the same through out rpm range say from 3000 to 6000 rpm at WOT. Just to throw out some numbers say 6% under drive might be 4lbs where 6% over might be 9lbs from 3000 to 6000 rpm.
Things that make you go hum??? :idea: You guys are selling me on the intercooler more and more even on low boost.
You are correct, both the blower and engine are fixed displacement air pumps, attached to each other. The amount of back pressure between the two is constant.
Rootes blowers were originally invented to move air through mine shafts at a high volume, low air speed and near zero pressure. GMC truck blowers were originally used to blow the exhaust gases out of the crank case of a 2 stroke diesel. They were fine for producing low boost in a low rpm situation.
If you are considering an intercooler, it will definitely help but you would be better off to get a big blower, turn it slow and not need an intercooler at all.

[paradigm shift]

Thanks DJ,
I totally agree on the big blower. For my set up I am thinking under driven and intercooled low boost on a 29' vee hull which equats to heavy loads over long periods of time running. My thinking or hope is that the intercooler would help it live as I am not so concerned with any HP gain of intercooler.
Going back to g935 question I'm thinking the bigger blower turning slower would make more power than a smaller blower turning faster which creates more heat and then intercooled to cool it down even with both running the same boost. Less back pressure without intercooler? Takes more HP to turn a roots blower at higher boost.
I guess the other debate is at what boost level does an intercooler start paying off? Guess that depends on blower size and how much you heat intake air. Questions never end. :)
Man I wish I had a dyno in my back shop to play with. :idea:

[Placecraft Dragstar]

http://www.supermotors.net/getfile/562197/fullsize/img_0298.jpg
That would make a nice boat engine, nice in that car as well though!!!!
The tractor pullers make awsome power and they are limited to 871 but they spinn the shit out of them. Some of them are spinning them at 75% to make the power they need.

[paradigm shift]

That would make a nice boat engine, nice in that car as well though!!!!
The tractor pullers make awsome power and they are limited to 871 but they spinn the shit out of them. Some of them are spinning them at 75% to make the power they need.
Tractor pullers running gas or alky?

[Placecraft Dragstar]

Tractor pullers running gas or alky?
ALKY

[HEAVYBOAT]

The 14% boost statement I assumed was a typo. As far as boost vs. blower speed, this could get really complicated! The true answer involves the kinetic theory of gases, laws of thermodynamics, the ideal gas law, and so on.
Simple answer:
A Rootes blower moves air. Period. Put it on top of an engine (another air pump) of a given size, driven by the crankshaft. If the blower produces less air than the engine can pump, you get vacuum. Spin it faster or make it bigger, move more air and you get pressure. This is fairly constant at wide open throttle regardless of RPM. When you see a higher boost reading as rpm goes up, it is HEAT, not more power.
Somewhat more complicated answer:
The faster a blower turns, the more heat it puts into the air. The air expands from heat, which creates pressure. The measurement of heat created vs. actual air density created is adiabatic efficiency. Around 40% to 60% for a blower. Centrifugals and turbos are much more efficient, they create boost by literally "throwing" the air molecules forward to impart velocity. The only real advantage of a rootes is that it moves air at low rpm as soon as the throttles are opened. That's what wins a drag race.
Even more complicated answer:
The kinetic theory of gases explains how individual molecules in a gas act and their relation to pressure, volume, and temperature.
This law has the following important consequences:
If temperature and pressure are kept constant, then the volume of the gas is directly proportional to the number of molecules of gas.
If the temperature and volume remain constant, then the pressure of the gas changes is directly proportional to the number of molecules of gas present.
If the number of gas molecules and the temperature remain constant, then the pressure is inversely proportional to the volume.
If the temperature changes and the number of gas molecules are kept constant, then either pressure or volume (or both) will change in direct proportion to the temperature.
Okay I'm going to quit now.:sleeping: :sleeping: :sleeping:
DJ
ahh, missed the nail.. Ill hit it for ya :D
One of the main reasons why roots blowers are so inefficient besides the big parasitic losses from driving them is the lack of Internal compression. Without that, theres nothing to stop the recycling effect from happening.
The turbos and prochargers by design have them therefore they get a "clean" cycle of air while its building boost.

[VDRIVERACING]

How does 14lbs. of manifold boost from a 1471 compare to the same boost put out by an 871? Will the volume of the larger blower at the same boost be any different power wise than a smaller blower? I understand that the temperature of the charged air might be different if the 871 has to spin faster, but what if that were equal?
Geoff
Thecharge temp being equal, the pressure(boost reading) being equal, then the volume of air and fuel is equal. I think the guys missed your "what if" the temp were equal comment.
Without going into quantum physics, an 8-71 pushing through an intercooler with 10-12 lbs of boost will knock your socks off. Unless the n-th degree of argument is at stake, it's less expensive per pound of boost! Have you priced a 14-71? Yikes.

[Nailhead]

14-71 on a 496 15% unerdriven should give me 12 lbs of boost. Run thru an intercooler, charge should be very cool.http://http://inlinethumb01.webshots.com/28416/2673527060102542672S600x600Q85.jpg (http://good-times.webshots.com/photo/2673527060102542672IqZKIY)

[HEAVYBOAT]

14-71 on a 496 15% unerdriven should give me 12 lbs of boost. Run thru an intercooler, charge should be very cool.http://http://inlinethumb01.webshots.com/28416/2673527060102542672S600x600Q85.jpg (http://good-times.webshots.com/photo/2673527060102542672IqZKIY)
Nice looking motor!
My example, an old combo of mine, 547ci with a fresh BDS Nylatron and Teflon, 1471 22% OVER still only made 14psi under the superchiller. Good flowing heads mind you, big cam ect. It must have at least seen a 6psi decrease in psi, combination of intercooler restriction and density change.
Your blower may out perform the BDS, and the heads and cam will play a part, but I still thought I would let you know my experience in case it doesn’t give the boost results that your expecting. All your looking for is power numbers I’m sure, so no sense getting caught up in boost numbers.
What’s the specs on the blower, hihelix?
Good luck

[Nailhead]

Nice looking motor!
My example, an old combo of mine, 547ci with a fresh BDS Nylatron and Teflon, 1471 22% OVER still only made 14psi under the superchiller. Good flowing heads mind you, big cam ect. It must have at least seen a 6psi decrease in psi, combination of intercooler restriction and density change.
Your blower may out perform the BDS, and the heads and cam will play a part, but I still thought I would let you know my experience in case it doesn’t give the boost results that your expecting. All your looking for is power numbers I’m sure, so no sense getting caught up in boost numbers.
What’s the specs on the blower, hihelix?
Good luck
Standard helix, billet rotors all fresh. Notice I put "should" make 12lbs. That just what the charts say. I'm hoping to get around 900hp on pump gas. This is just a ski boat motor that won't see past 6000rpm.

[HEAVYBOAT]

Ya, those charts cause more harm then good. ;)
900hp? Dont think thats going to be too tough. That 14psi combo I spoke of made over 1140hp. :D
And I'll pass on the water sking behind that thing!! LOL

[Nailhead]

Ya, those charts cause more harm then good. ;)
900hp? Dont think thats going to be too tough. That 14psi combo I spoke of made over 1140hp. :D
And I'll pass on the water sking behind that thing!! LOLIf your not skiing than how about a tube ride? :eek:

[sanger rat]

14-71 on a 496 15% unerdriven should give me 12 lbs of boost. Run thru an intercooler, charge should be very cool.http://http://inlinethumb01.webshots.com/28416/2673527060102542672S600x600Q85.jpg (http://good-times.webshots.com/photo/2673527060102542672IqZKIY)
Nice piece. How is that Blower to carb spacer working out for ya? Does it have a divider in the middle?

[Nailhead]

Nice piece. How is that Blower to carb spacer working out for ya? Does it have a divider in the middle?Thanks. No divider, just a spacer to reduce the opening from the large buzzard catcher opening to the more standard opening. I havent run the engine yet, It will be a few more weeks till I get it to the dyno.

[sanger rat]

Thanks, Post the results when you get them.:)