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| AMR 300 https://www.ausmini.com/forums/viewtopic.php?f=2&t=69092 |
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| Author: | Kennomini [ Thu Mar 03, 2011 5:46 pm ] |
| Post subject: | |
Can I get this all explained please. The air we are in is 1 atmosphere which is the same as 1 bar (which is 14 PSI) Correct  or is it classed as 0 bar
This is the SC14 on my Feroza, it is direct drive (no clutch system). 
When this system is at idle (800-1000RPM) the boost gauge reads VAC 20 (-20 PSI correct ) which is below atmospheric pressure
When the car is on boost (6 PSI) is that 6 PSI above the 1 bar out side the engine
More questions to come after this lot is explained.... |
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| Author: | mini_mad_matt [ Thu Mar 03, 2011 6:22 pm ] |
| Post subject: | |
I'll start by saying my physics/chemistry is pretty sketchy. So sorry if what i say is wrong. Atmospheric pressure is measured at 14.7 pounds/square inch at sea level. That pressure corresponds to the weight of air holding a column of mercury 29.92 inches in height So when you are talking about Pressure, you are talking above atmospheric pressure. So when your gauge tells you 6psi boost, then this is above atmospheric. And so your vacuum of "20" is really saying 20inhg below atmospehric. (i think) |
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| Author: | Mokesta [ Thu Mar 03, 2011 8:13 pm ] |
| Post subject: | |
There is "Gauge" pressure and "absolute" pressure. A typical boost gauge reads pressure above/below the 1 atmosphere that you have normally. To get absolute pressure add 1 atmostphere to gauge pressure. So, you can have negative gauge pressure down to -1 atmosphere but you can't have negative absolute pressure. Zero is as low as you go. M |
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| Author: | Kennomini [ Thu Mar 03, 2011 10:12 pm ] |
| Post subject: | |
Yep that is pretty much what I thought. Atmosphere is the same as 'bar' which is 14.7 PSI. Any boost is on top of that standard air pressure so in a way a N/A car is running on 14 psi, it's just technically not boost. That'll be fun to bring up down the pub  .
Thanks guys. |
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| Author: | sgc [ Thu Mar 03, 2011 10:28 pm ] |
| Post subject: | |
Kennomini wrote: Atmosphere is the same as 'bar'
.. which is an abbreviation of 'barometer' or 'barometric', hence 1 bar is 14.7 PSI at sea level, or atmospheric pressure 
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| Author: | david rosenthal [ Fri Mar 04, 2011 12:36 am ] |
| Post subject: | |
most pressure guages are set at zero for atmospheric pressure. So zero is actually 14.7 psi. The correct guage for a blower is either a compound guage where zero is zero [no pressure] or you get a correct calibrated guage. What you have to understand is that a blower is a positive displacement 'pump'. Exactly the same as a gear pump, vane pump or a lobe pump [like the mini oil pump.] A postive displacement pump is one that will discharge a constant [well almost allowing for leakage] volume of fluid or gas for a single rotation. So look at the rotors in a SC type blower, the vanes have a valley and a peak, and as the rotors are timed the peak of 1 rotor will mesh into the valley of the opposing rotor. Now as the rotors are turned the peak comes out of the valley [inlet side] and this means that the volume is increasing ,so the air at 14.7psi fills the total valley. The rotor turns so the air in the valley is carried around the outer case diameter until it reaches the discharge side and then the peak will start to move into the valley. The volume is decreased and the pressure then increases and the air is forced out. This is the compression part of a blower. If you did not have this action then the air would just circulate and the pressure would be the same on both sides. As the air is being discharged into a closed area[ ie not open to atmosphere] there is not initial pressure. So if your guage is set at zero[not allowing for atmosphere] and you have a pressure of 14.7 psi you have exactly the same as a N/A engine. Usually boost is measured as atmosphere plus pressure above atmosphere. One of the most efficient superchargers made is the scroll type that were fitted to the rolls royce merlin engines. These used a system like a spintrex that also did compression in the last stage of the rotor movement to give the air velocity. The scroll blowers are just a "flat version" of these but as they were a blow thru system and geared to supply 3 to 4 times the vloume they had a pressure valve between the suction and discharge. Being a aircraft engine they needed full boost at low altitude especically for climbing , but at higher altitude the volume required was less so the pressure valve would compensate. Wartsilla and MAN 2 strokes run scroll blowers on them to give the engine power at low revs until the turbos kick in and then supply the air to the scavange trunk. Pielsticks run a very effieicent liquid ring seal blower that has water in the case to seal the rotors and they are boosting upto a total pressure of 3.5 bar. |
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| Author: | 1962CKD [ Fri Mar 04, 2011 6:09 am ] |
| Post subject: | PV=nRT |
My 2 bits - Using the general gas equation for this application is like trying to use binary to uncode the brain! Using venturies and expansion chambers on a well set up supercharger system is a waste of time as you get no real temp drop when driving. PV=nrT P: A venturi to increase pressure or expansion chamber to reduce pressure is mute considering the balance of energies from the supercharger exit "P" to the engine inlet "P" is what we want to be the same. V: We want the volume of the air/fuel to go up where possible. Thats why it's "charging" the engine. Pulling "V" down to get temp down, doesnt make sense, you may as well take the supercharger off if it were logical. n: number of mole (not in this discussion) r: constant (google it) T: This is where the action is. Before the engine we need to keep temp modest for best power production. Take T down and Pand V come down according to the equation. In practice V doesnt come down as the inlet manifold doesnt change size dynamically and so P comes down. Thats why the super charger efficiency is important it lifts P but T is always loosing. If you're chasing a thermodynamic efficiency increase to move heat out of the charge then the proven application is intercooling (surface area conductance and temperature differential) my 2 bits |
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| Author: | david rosenthal [ Sat Mar 05, 2011 12:41 am ] |
| Post subject: | |
well 1962CKD you googled it. Fantastic. Now do some study on thermodynamics [the 2nd law] and while you are at it look at the rest of the gas laws, not just the basic law. Now as for a venturi also look up what happens to gas flows thru one, and while you are trying to figure it all out do some calculations on loss of efficiency and increase in friction[ that generates heat] of a gas flowing thru a inter-cooler. All those tubes create a loss of air velocity and generate heat. The only cooling you get is the heat transfer to the temperature of the cooling medium. that's calculated as Watts per square meter. So tell me what is more efficient, air flowing thru a venturi, the calculation for that is loss of pressure energy=gain in kinetic energy IE P1xV-P2xV=[1/2mV2]squared-- [1/2mV1]suqared. so the air has a mass,pressure ,volume and temperature when it comes out of the blower,and you then increase the velocity[kinetic energy] and the pressure in the chamber drops. BUT look at what I said. The air will cool[unless you have prooved the laws of physics wrong] and then the air is passed thru ANOTHER venturi from this chamber into the plenum chamber connected to the carbys. The air again will have a pressure drop but increase the velocity. So we now have the same mass of air[which is the base for air fuel ratio for combustion14.8LBS of air to 1LB of petrol] that is travelling faster than the original velocity out of the blower[ higher kinetic energy] and that's what engine performance is about . The greater MASS [IE density/volume] of air into the cylinder. OR air coming out of the blower that has to be pushed thru tubes[intercooler/restriction/friction] before it gets to the carbys. The expansion chamber I am refering to' is positioned in air flow to assist in the cooling, but does not have restrictions. Just for clarity I am refering to a blow thru constant pressure system not a suck thru a carby where the blower is sitting on top of the extractors getting the air heated up. |
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| Author: | 1962CKD [ Sun Mar 06, 2011 8:35 pm ] |
| Post subject: | whoa there tex |
nice I wait eagerly to see your system.
PM sent |
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| Author: | Mokesta [ Sun Mar 06, 2011 8:49 pm ] |
| Post subject: | |
Oh, please share!
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