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I've been considering getting a set of underdrive pulleys, but I had a question about them. I've heard that after installing them, the alternator doesn't provide charging power during idle. Would it be possible to get a higher output alternator that even though it spins at a lower speed would provide just as much if not slightly more power than the stock alternator with the stock pulley?

Also, I've had this idea tossed to me and I've been wondering about it's feasibility. The A/C compressor pulls a lot of HP from the engine. Would it be possible to completly remove this load from the engine?? The idea is to get a high-torque DC motor that runs off of minimal power (maybe 10 or so amps) that would power the compressor. This could be tied in to the alternator idea where the alternator is providing more power which would help keep the electrical system okay. This would leave the A/C compressor completely off of the engine even at Max A/C.

I'm just curious as to whether either or both of these ideas would work. Any comments?
 

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I'm sure some of our engineer type FocalJet members can elaborate more on this, but what you propose is akin to a perpetual motion machine. Thermodynamics doesn't allow you to get something for nothing in the power department.

The higher output alternator would provide more resistance and even though spinning at lower rpm would consume more engine power than the stock unit at standard rpm.

The A/C compressor consumes very little if any HP from the engine when it is not engaged. At wide-open throttle, the Focus automatically disengages the A/C clutch. So when you need engine power the most the A/C is of little worry. It may be possible to rig a high-torque DC motor to power the compressor (all-electric automobiles do this), but the dollar cost would be fairly high, and these dollars could be better spent elsewhere on a CAI or exhaust that might result in proven gains. You also have to factor in the considerable weight of the electric motor and possible extra batteries needed to power it.
 

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I'd say the 3 peice kit really isnt worth the hassle. Just get a crank pulley (the lightest is the esslinger, but i've heard that the AFX is smaller) either way you're getting a good part. I've never seen my car have any charging difficulty, and that A/C idea is intrigueing but, as an EE i think the motor you'd need would be far too power hungry for a car's generator. If you care enough just get rid of it, and save some weight too.
 
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