boost question

[Rod&Custom]

The power is, but isn't necessarily made by pressure, as you are talking. But it is the pressure which condenses the molecules which causes better atomization with the fuel, causing more power. You make it sound like the pressure is forcing the piston to move or something, when in reality it is just easier for the flame front to spread quicker when the molecules are closer together. PSI isn't always good, look at detonation!

[krisw]

Originally Posted by -Jayson-

ive got a good analgy for this guy. ok lets say you have two ballons. One is a normal sized party Ballon the other is a tiny water ballon. Now you fill each balloon to eactly 4 PSI. Now the smaller balloon occupies much less space than the bigger balloon. So it order to make it reach 4 PSI it doesnt take nearly as much air. Where as the big balloon take sup alot of space, and reaching 4 PSI will take alot more air.

I honestly dont think you know what PSI is, or understand the physics of air volume/air pressure/ and air mass.

ok your analogy doesnt really explain much for me either. im talking the same size engine here, 2 different sized superchargers one engine. now the way i read your analogy is that the engine would be the balloon, and filling a smaller balloon (engine) to 4 psi takes less air than filling a big balloon (engine) to 4psi. yes that obviously makes sense. thats not what im talking about though. if thats not the analogy you were trying to make then i have no clue what you are trying to say. i guess you could be saying that the balloons are superchargers? but then youd be pointing out that it takes more air to fill a bigger supercharger to 4psi, but why would you fill a supercharger to 4psi? i appreciate all the replys, i just wish someone had a logical explination that i could understand.

[silverstangs]

Let me give this a shot

1 engine 3 different blowers and lets say they all hit 15psi of boost.
First is a Centrifugal blower.
Second is a Twin Screw blower.
Third is a Roots blower.


The centrifugal supercharger: The centrifugal supercharger is a fan, that pulls air in and will hit 15 psi at a higher rpms because it uses the rpms to build centrifugal force, which makes the air move from the center of the fan to the outside of the fan blades where it gets scraped and directed thru a small hole into a scroll. The scroll is that tubing that looks like a snail shell. The tubing gets wider as you go further away from the hole, which slows down the air thus creating the pressure aka "the boost". This type of supercharger does not displace any location because it's rotating part does not move into or out of a location that air occupies.


The Twin Screw and Roots blowers are positive displacment superchargers. The rotating mass within each section moves into and out of a area that air will occupy. Before I explain how they work I need to give you few base statements.

Air, just like water and electricity will go where there is the least amount of resistance. If you suddenly create a vacume, air is going to want to fill that vacume. Air also act like or mimick a ball, in that it will follow a curve, and just like a ball, if you have two long screws or twisted wedges that are parallel to each other, but have the threads facing the opposite direction, and you have them spining to the inside of each other, or the outside of each other, the ball will either go down the screws or up the screws, or down the wedges or up the wedges

The twin supercharger: The twin screw supercharger is actually a compressor. The twin screws slices the air that naturally comes in at the inlet when the tips of the twin screw vacate and then occupy the opening of the case. Each time the tips of the screws unblock the opening, it creates a vacume, and that's how the air starts it's path into the supercharger. As the air moves down the pair of screws, it gets squeezed,and that creates the pressure, and thus is pressurized before it gets to the intake.

The Roots Blower: The Roots blower folds air into the intake, and is really the only blower out of the three types of superchargers. The roots design was originally meant to force air down mine shafts. It works by taking air from the top or bottom of a set of blades and moving the air to the opposite side. It has 3 basic twisted wedge shape. Just image two triangles sitting with one edge on the bottom and both triagles attached by three pipes. Now take one triangle and turn it 1/3rd of the way over so that one of the sides is now on the bottom. That's basically what the roots wedges looks like. You have two of those again mirroring each other, so that as the wedge rotates, the air moves diagonally across the case, either from top to bottom or bottom to top. Where ever the air end up at is where the boost is created. FOr a car, that's basically in the intake, and that's where the actuall compression takes place as the air is folded into it. Best example would be your mom's cake mix with it's two blades. As the blades move inward to each other, the batter is pulled in where the blades meet and pushed out where the blades seperate. Where the batter is pulled in is the vacume in a roots blower, and where it is pushed out is where the compression is.


I hope this helps you out. I made it as generalized as possible.

Also the screws are "tighter" or "Closer" to each other than the wedges, so they form a closer seal to each other. The Roots blower does not seal the air as well from the "positive" side to the "negative" and the part of the air that has been folded into the intake gets "recycled" as the wedges rotate. This does not occure with the "Twin screw" superchargers. Also because part of the air is "recycled" that air that is compressed in the intake is warmer than the air drawn in thru the opening of the supercharger. The problem with this is that the warm air will heat up the entire lenght of the wedges as well as the casing. That's why Roots style blowers are not as efficiant as the twin screw blowers.

[krisw]

yes i know all about superchargers, i know what centrifugal, twin screw, and roots blowers are... thats why i have a twin screw =). but none of this answered my question. just so you all know im not a moron, i know an enormous amount about cars, engines, superchargers, volumetric efficiencies, barometric pressure, all that... which is exactly why im asking this question. now since this topic has gotten on a tangent it seems like, i would like to reiterate my original question. an eaton m90 and an eaton m45 are both roots type superchargers, and as the name would imply the m90 is twice the size (flow wise) of the m45. now assuming you took these superchargers and put them on the exact same engine, each one pushing 10psi, would one actually be flowing more air than the other? if the answer to this is yes then explain to me why. i know that every person who reads this will of course say that the m90 is flowing more air, but why! im trying to figure out how it can put more air in the intake system and still be applying the same psi thru that system. am i just looking at this horribly wrong? or does an m45@10psi flow the same amoutn of ar as an m90@10psi? (of course there will be differences in the power output due to volumetric efficincies of each blower, the amount of power it takes to turn them and so on, but just strictly based upon theoretical airflow, will they be the same or different, and if different explain to me why that is)

[SkylineUSA]

If you cool your intake charge what happens to the PSI of that charge? Will it stay the same, increase, or drop?

It will drop! But now more volume is now able inter in the same space, so you can increase the volume for the same psi. Get it?

With that increase in volume, you get more power, since there is more air.

The 45 will heat the air more, which has been stated before, so you lose power because the air has expanded. Like I said it has to do with volume, not psi. Psi does not tell you much, unless everything is equal in an engine when dealling with any type of boost powre adders.

Its all about the CFMs baby

[-Jayson-]

ok i think i get your question now. PSI is relavent to the engine size. The bigger the engine, the MORE air and pressure needed to make PSI. The engine can only take in so much air on its own, now PSI as you should know is a measure of force, not mass. But when it comes to engines, the force and the mass are the same thing. Because two of the same engines can only take in so much air at the same time. Which means it will take the exact same amount of air being forced into the engines to make 1 PSI.

Ok now lets forget about efficiency and heat created by the blowers for a minute. Now if you had a M45 and a M90, but them both on the same engine, and set them up to run 10 PSI on both engines, you would be flowing the EXACT same amount of air. Theoretically of course. But the M45 would have to be spinning twice as fast to make the same amount of PSI, but it would still be flowing the exact same amount of air.

So yes, a M45 making 10PSI on one engines moves the exact same amount of air to make 10 PSI than a M90 does to make 10 PSI on the same engine. Only difference is, the m90 does it with only half the speed required of the m45.

[SkylineUSA]

Originally Posted by -Jayson-

ok i think i get your question now. PSI is relavent to the engine size. The bigger the engine, the MORE air and pressure needed to make PSI. The engine can only take in so much air on its own, now PSI as you should know is a measure of force, not mass. But when it comes to engines, the force and the mass are the same thing. Because two of the same engines can only take in so much air at the same time. Which means it will take the exact same amount of air being forced into the engines to make 1 PSI.

Ok now lets forget about efficiency and heat created by the blowers for a minute. Now if you had a M45 and a M90, but them both on the same engine, and set them up to run 10 PSI on both engines, you would be flowing the EXACT same amount of air. Theoretically of course. But the M45 would have to be spinning twice as fast to make the same amount of PSI, but it would still be flowing the exact same amount of air.

So yes, a M45 making 10PSI on one engines moves the exact same amount of air to make 10 PSI than a M90 does to make 10 PSI on the same engine. Only difference is, the m90 does it with only half the speed required of the m45.

No it does not move the same amount of air, the volume is different because of heat, and compressor size!

[SkylineUSA]

Don't look at pressure, look at volume. When you look at superchargers what do the list, psi? Nope! Do they list cfm? Yep! I wonder why that is? That's right PSI does not tell you everything. I will say it one last time, VOLUME

Do you get it now? I have just said what boosted did, but with a little different approach.

[SkylineUSA]

krisw,

Do you get it, if not re-word your question.

[krisw]

so would jayson be correct in saying that in theory, without taking heat and thermal expansion and whatever into account, the m90 and the m45 would be flowing the exact same amount of air at 10psi?

[SkylineUSA]

Originally Posted by krisw

so would jayson be correct in saying that in theory, without taking heat and thermal expansion and whatever into account, the m90 and the m45 would be flowing the exact same amount of air at 10psi?

Of course not, you still have volume.

Put it this way.

The 45 10psi at 250cfms, would be equal to a 90 at 5psi at 500cfms, roughly.

[tturnpaw]

Originally Posted by -Jayson-

ive got a good analgy for this guy. ok lets say you have two ballons. One is a normal sized party Ballon the other is a tiny water ballon. Now you fill each balloon to eactly 4 PSI. Now the smaller balloon occupies much less space than the bigger balloon. So it order to make it reach 4 PSI it doesnt take nearly as much air. Where as the big balloon take sup alot of space, and reaching 4 PSI will take alot more air.

I honestly dont think you know what PSI is, or understand the physics of air volume/air pressure/ and air mass.

he should have gotten it by now. I dunno who couldnt understand that. lets just say at a lower rpm boost builds earlier than a smaller supercharger/turbo and will hold longer or gain even more. or would underdrive pulleys give you a feel for work on an engine? oh well i got it.

[tturnpaw]

Originally Posted by silverstangs

Let me give this a shot

Now im all confused! lol, i dunno if im baking a cake or building an engine! jk

[tturnpaw]

Originally Posted by krisw

so would jayson be correct in saying that in theory, without taking heat and thermal expansion and whatever into account, the m90 and the m45 would be flowing the exact same amount of air at 10psi?

The best thing ive ever heard about an engine is that they are all about air flow. The faster air goes in, the faster it comes out, the more power built. air in+air out=more power built. its like putting on a set of heads on a stock motor. they flow a lot more and easier, making more power.

[silverstangs]

Originally Posted by tturnpaw

Now im all confused! lol, i dunno if im baking a cake or building an engine! jk

Neither, I thought I was building a house