Turbos is not more efficient at all......
A supercharger does indeed require power to drive it. The power required is actually mass airflow times boost. You also need to include the extra power required due to efficieny losses in the blower caused by heating of the air above that which occurs because of compression. Also belt drive losses need to be taken into account.
If you do the maths you will probably find between ten and twenty percent of crankshaft power is lost driving the blower in a typical modern street engine.
Now a turbo also requires power to drive it. The power developed by the exhaust turbine is once again mass airflow times boost, plus efficiency losses, plus bearing losses. If your supercharger has 70% adiabatic efficiency, and your turbo runs at about 70% adiabatic efficiency then the actual shaft horsepower required is going to be identical !
But to drive the exhaust turbine there must be a pressure drop across the exhaust housing and turbine wheel. This is basic thermodynamics. you cannot get power out of something without putting power in.
If you have ever measured the pressure drop across the exhaust turbine you will find it will be typically betwwen twice boost pressure, down to the same as boost pressure if you are really lucky.
But how does this extra back pressure in the exhaust manifold effect engine power ? Well again research has been done into this and the results have been published.
Typically an engine looses 1% of crankshaft power for each psi of back pressure in the exhaust manifold. Surprise ! ! you are going to lose about ten to twenty percent of crankshaft power to drive your turbo, exactly the same as that required to drive a supercharger.
Ah but if you loose 1% of power per psi that means at 100psi back pressure you would have no power at all ? Yes indeed.
When the exhaust valve opens there may be roughly about 100psi left in the combustion chamber trying to get out. If there is no exhaust flow, the engine will stop. Hence zero output power.
The myth that superchargers draw power from the crank, and turbos are free power for nothing is just that, a myth.
(thx Warpspeed)
With my engine (RB30ET) I'm building a system with both a turbo and blower (Blower is a SC14 off a Toyota Crown @ 9psi).....No turbo lag and great topend power
Anyway my Supercharger cost me $350 Aus (about $160 US) so they are not expensive at all. Now for you smaller 2L engines a SC14 is a bit large, maybe a cheaper blower off a Suburu or sumthing would be better (seen one @ 10psi on a SR20DE) anyway these blowers are cheaper @ $175 AUS.....good stuff
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