- Nov 23, 2004
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hi all, i am new. just want to know how boost is measured is it by the pressure in the cylinder or in the turbo? as someone was telling me that 1bar reading on a small turbo is different from a 1 bar on bigger turbo.
ermmmm confusing here. cfm means cubic feet per minutes...then should be nothing to do with 1.2bar or 1.5bar.Originally posted by Battousai@Nov 24 2004, 00:03
let musang padawan tell u what i know..
so, cfm in real world means how fast a turbo can reach it's full boost (that we set), .
Actually, its how much air the turbo can flow at its peak efficiency. If, for example a turbo is at its peak at 1.2 bar, when you boost it up to 1.5 bar, you start losing power because the air is too hot, the turbo is spinning too fast and it simply cannot flow that much air. When you push the turbo too hard (high boost, high RPM) you'll find boost pressure starts to drop off.
turbine side...ermmm this is more like LAG.Originally posted by Battousai@Nov 24 2004, 01:35
How fast it reaches full boost depends on your turbine side
aihhh..tired of explaining la.Originally posted by flamefox850@Nov 24 2004, 02:22
hmmmmm
cfm still cubic feet per minute means how much volume of air can be blow in a minute. higher cfm = faster air flow (same boost) or higher boost (same time)
about the small compressor VS big compressor and how small compressor generate more heat..u all can read here :
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"Compressor
The compressor is the part of the turbocharger that compresses air and pumps it into the intake manifold. Air molecules get sucked into the rapidly spinning compressor blades and get flung out to the outside edge. When this happens, the air molecules get stacked up and forced together. This increases their pressure.
It takes power to do this. This power comes from the exhaust side of the turbo, called the Turbine. Not all of the power that comes from the turbine goes into building pressure. Some of the power is used up in heating up the air. This is because we lowly humans cannot build a perfect machine. If we could, all of the power would go into building pressure. Instead, because of the design of the compressor, the air molecules get "beat up", and this results in heat. Just like rubbing your hands together will warm your hands due to the friction between your hands, the friction between the compressor and the air and between the air molecules themselves will heat up the air.
If you divide the amount of power that goes into building pressure by the total power put into the compressor, you get the efficiency of the compressor.
For example, if the compressor is 70% efficient, this means that 70% of the power put into the compressor is used in building air pressure. The other 30% of the power is used heating up the air. That is why we like high efficiency compressors; more of the power is being used on building pressure and less is used heating up the air. Turbos, Paxtons, and Vortechs are all centrifugal superchargers. The are called this because the centrifugal force of flinging the air molecules from the center of the housing to the outside edge is what builds air pressure. The maximum efficiency of these kinds of superchargers is usually between 70% and 80%. Roots blowers, like the 6-71, work differently and have much lower efficiency, like about 40%! With those, when you try to build lots of boost you have to put in a lot of power and more than half of it gets used heating up the air instead of raising pressure."
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so, conclusion is efficiency rate that decide a good or bad turbo in terms of heat generates not CFM. higher efficiency means less heat generate and this often occur with bigger compressor.
bigger compressor blades less 'grind' the air for given boost thus making more hp.
with high efficiency turbo, less heat generates then more air flow..bigger cfm means more air can be pump in less time
*revision : Compressor flow rate and efficiency