Quote:
Originally Posted by ShizzySupra
It is due to displacement. Smaller displacement motor benefits more from the smaller blower. Ford guys also have a transbrake trans.
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I'm sorry, that is not a correct statement, engine displacement is always your friend. More displacement and/or RPM should always make more power, if it doesn't - you messed up something else along the way. Ford guys don't have displacement but they have good heads which lend themselves toward the RPM side
A supercharger is simply an air pump, you want one that has the flow capacity that you need and the highest "Compressor Efficiency" (which includes mechanical losses of the compressor) to make the most power - this is not to be confused with "Adiabatic or Isentropic Efficiency" (which are measurement of only the thermal component - neglecting the mechanical losses of the supercharger)
A positive displacement SC delivers a given amount of air at a given speed period. Barring SC inlet side restrictions, there is no way to make it flow more without spinning it faster. If we add displacement to an engine and keep the same pulley ratio, the airflow into larger engine will be essentially exactly the same - but the supercharger will be operating at a lower Pressure Ratio. (lower boost pressure for the exact same airflow)
The power required to drive a supercharger (no matter what type) is comprised by the following 3 items:
Mass Flow
Pressure Ratio
Frictional Losses
Since the SC speed is the same - mass flow and friction will not change, we are now on a larger engine, so the pressure ratio will decrease - resulting in decreased input power to drive the SC. If the larger engine is geometrically the same (same compression ratio, similar in cylinder motion, port airflow increased with displacement) the larger engine will make more power with the same SC speed compared to the smaller engine specifically for the following reasons.
Less power consumption from the SC
Lower pressure ratio provides less heat and allows for more ignition timing.
Now while this is all fine and dandy, we didn't increase displacement to have a small power gain, so now we'll go ahead and increase blower speed up to the limit that the SC or Engine can handle to maximize the return on our investment...
