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Originally Posted by MNBoxster
Hi,
An Alternator's parasitic draw from the crankshaft is variable. It can range to almost nothing (maybe as low as 0.05HP) to as high as 30HP depending upon how much electrical demand it's being asked to supply.
Alternator's are not very efficient so far as power generation in a car is concerned. First, they produce Alternating Current (AC) for a machine designed to use only Direct Current (DC).
In order to convert this AC to DC, the current is passed through a series of Diodes and Rectifiers which results in tremendous losses (mainly as Heat) due to inefficiencies.
Happy Motoring!... Jim'99
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A couple of points...
I beleive you're overplaying the role the alternator would have on the test performed. The car's battery has one primary function... to start the car. Once started, the alternator has two jobs... to top off the battery's charge, and to power the car's electrical system.
Topping the battery back up after starting would be a small load, and is essentially repeatable. The large HP drains you're quoting would only be present if you were running many peripherals such as headlights, brake lights, ventilation fans, rear window defogger, etc. As long as the test were done with the same loads on the alternator each time, the difference should be insignificant.
In fact, as the car is shut down and restarted for subsequent pulls, the battery would lose some of it's charge each time, and the load on the alternator would be larger on each pull. If that's the case, he should have seen the HP go down on the later pulls as the alternator works harder to charge the battery back up. Since the HP went UP, that seems to bolster the case for the snorkle slightly restricting the airflow, and its removal making a small, but measurable difference.
The fact that diodes (which are the same things as rectifiers) generate heat as they pass current has absolutely nothing to do with whether or not snorkle removal makes more power. Non sequitur.