Quote:
Originally Posted by serialk11r
Alright my bad, but I fail to see how it is more intrinsically efficient at all...both adiabatically compress incoming air. If I'm wrong, could you point out what exactly is wrong with my thinking? In fact if twin screw has internal compression going on, then it would be less efficient if the boost pressure is lower than the pressure than the compressor produces, if I understand it correctly.
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Adiabatic compression is an ideal, and so, does not exist in the real world. That's what the term 'adiabatic efficiency' is all about. It's how much work it
should take to compress the air, divided by how much work it
actually takes. The difference between those two numbers is all going into the air as heat. That's why people make such a big fuss over compressor maps. Roots, twin screw and centrifugal (and by extension turbos) superchargers all have different adiabatic efficiencies (between the types, and between different models). Even a single supercharger has varying efficiency throughout it's operating range. So you need to use a sc or tc that is efficient under the conditions you want it to operate under.
Anyway, twin screws generally have higher adiabatic efficiencies than roots blowers, especially at high boost levels. But you are absolutely right about that last part, though mostly it comes into play in part throttle situations. If there's vacuum behind the throttle plate the bypass valve opens. With a roots blower this is great because it totally unloads the SC and the parasitic losses drop to nearly nothing. With a twin screw, the already compressed air is simply allowed to re-expand uselessly and all the energy that went into compressing it is lost. So on a daily driven street car, a roots blower will give better fuel economy than a twin screw. But at full throttle, a twin screw will provide lower BSFC (and more power) since the higher efficiency means lower parasitic loss.
Quote:
Originally Posted by Lucas
Compression ratio doesnt effect turbo response. Just sayin
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You're wrong. Just sayin