What is Boost?

Question

So boost is measured by how much the air is compressed because when the volume decreases the pressure increases and if you increase the volume of air and compress it you have a higher boost pressure? Or is boost pressure how hard the turbo is working to pump the air? I read that on a website? Is this correct? How can you be producing more boost when at lower air masses than at higher air masses? Example 9psi@30lb/min 20psi@20lb/min How is this possible? Is it becaus eof turbine shape, design, weight, material do all those factors come in play? When there is more pounds of air flowing wouldnt there be more boost because more air is flowing so more air is being compressed? Or does it depend on volume rather than pounds? Can you please explain this to me in detail?

Answer 1

If you you care to look up an internal drawing or picture of any turbo charger and complete manifolding things will be more clear. My words will not replicate a good picture or drawing. Inside a turbocharger there two schroll shaped fans seperated by a cast iron wall and a crankcase oil pressurized bearing in the center. These fans spin in a very close tolerance dual fan housing. The hot exhaust gasses spin the hot side of the turbocharger at very high rpm's by means of a manifold system. It's not unusual for the exhaust gasses to cause the hot side of the turbo 10,000 - 20,000 rpm's depending on the application. The hotside turbo drives the atmospheric side by a 1-1 common shaft seperated by the bearing and cast iron sealed wall.
The opposite side turbo fan again is closely fitted by the outer cast iron housing. As the intake side fan spins it creates a vacuum infront of it and as the gathered air passes through the high rpm rotating fan air is greatly compressed causing heat. This compressed heated air on most turbo motors is forced through a inner cooler. The sealed coolers can be an air to air, air to water or air to cooled water. The idea behind this is to reduce the temperature of the compressed air so it contains more oxygen and provides more dence pressure before each intake valve opens. Turbo chargers are responsible for filling the cumbustion chambers with cool compressed air greatly improving filling efficiency, power and more importantly torque and fuel economy. These traits are exceptional in diesel motors. Depending on application the compressed air (boost) is controlled by a pop- off valve. Some street applications are set as low as 15 - 22 pounds of pressure before any excess pressure is released to atomosphere. The amount of perssure (boost) is regulated as a sefety measure by car and truck manufactures so the motors will live and not be damaged by the added turbo pressures.

In racing applications where there are as many as 3-4 chargers working in line and 60-120 pounds of BOOST pressure is not unusual.

In pulling tractors, modified the high pressure fuel injection pumps force in enormious volumes of diesel fuel directly into the combustion chambers. High pressure car wash pumps release water into the pressure side of intake manifolding to keep the high compression (18 - 22) to one compression ratio combustion chambers cool enough so that the aluminum forged pistons will not melt. These highly modified pulling motors easily put out 1,800 - 4,000 horsepower depending on cubic inch size.

All boost really means is a slang term for inctrased air pressure generated by the spinning of the intake side turbo-fan inside the very precision gap housing.

Hope I haven't confused you. Good Luck! I really don't want points. I answered to the best of my ability. I'm no English major by a long shot !!!

Answer 2

Lbs of boost is just that, pressure. It is only semi related to lbs of air. Lbs of air is a measurement of the mass of all the atoms in the air. Depending on the space between those atoms, you can get different boost rates with different lb/min rates, and not necessarily scaled accordingly in the real world. In a controlled environment, or in mathematics when you change nothing else, would be the only time that the two are actually related. Meaning that in the mathematical equation (with all other variables staying the same) more boost/pressure would always equal more air mass. However in the real world it doesnt happen like this, the act of compressing the air itself causes the molecules to hit each other and makes heat, which right off the bat means more boost = more heat, no other variables accounted for. All of this said, more boost generally DOES mean more mass of air as well, as the other variables 90% of the time dont matter enough to offset the simple act of pushing more air. Just remember that everything has a threshold, and there are diminishing returns the further past what would be optimal you go.

Turbo design can and does have an effect on the end result, which is why there are different sized turbos, each with a range that they are more efficient in. A larger turbo will be able to produce more air (CFM) out the compressor side (and make it cooler than a smaller turbo), but take more air (CFM) to move the turbine side. Depending on the size of the motor and the desired boost pressure and RPM that you will get to positive boost, is how you pick what would be right, bigger isnt always better.

All of this assumes the same size displacement/air entering an engine per cycle. If you change the size of the engine then it should be obvious that you will flow more air at lower boost pressures.

Hope that is what you were looking for.

Answer 3

It is the amount of air the turbo is drawing into the engine. The boost gauge measures the amount of flow by reading the amount of vacuum on the intake side of the turbine this lets you know how much air is flowing through the turbine and going into the engine. Nitros increases the amount of boost because it has more oxegen and causes the fuel to ignite better which causes the engine to have more horsepower and build rpms faster which in turn causes more air to go
through the turbine and increases the vacuum on the turbine
intake which shows that you have more boost on your gauge.

It is the volume of air that is how it increases the compression, by allowing the engine to pump the pistons more quickly it increases the amount of compression and one causes the other to increase more rapidly the boost pressure is lower at a higher rpm because the air is flowing through the engine more quickly and freely.

Answer 4

very simply boost is positive pressure created by a turbo or blower, also referred to as forced induction. pressure is created by packing a larger volume of air into a given space by compressing it. the amount of volume is limited to the amount of space available and the amount of pressure or boost that the blower or turbo is capable of.
without a blower the engine and atmospheric pressure are the only factors involve in pumping air through the engine, when a forced induction system is added, the air can is pumped into the engine which raises both pressure and volume, with more air you can add more fuel which makes a larger explosion, creates greater volumetric efficiency which all boils down to more horse power.