look for a stock size light weight alternator pulley, i can tell you right now the underdrive pulleys even though they are larger they are less then half the weight of the stock alternator, so i would imagine is the stock size light weight pulley would be even lighter then the underdrive one. But when you break the 600ish watt mark your alternator wont put out enough to truely make a difference. So you will want to get a capacitor to keep your headlights from dimming ^_^

 

I already have a cap. I dont remember if its .5 farad or 1 farad. I put that in when I put the amp in, because I planned on adding another amp later. Still havent gotten that far though lol.

 

yeah, im probably going to have to add a cap after i drop the 1200watt amp i just ordered...... cause thats going to be 1600 between the two amps and the lights dimmed even with a 160amp alternator running at idle
too bad it only pumps 70amps at idle

 

1. R134a is 10% less efficient than R12
2. R134a has to operate at a HIGHER pressure to get similar performace
3. R134a has less reserve capacity than R12 does

when you lower the compressor speed you are lowering the system pressure thus reducing the cooling performance. If you live in an area where it gets maybe 90 you may not notice but if you live somewhere like Arizona, then you are going to feel it

 

hehe, yeah, it would be very bad to have the AC underdriven in AZ But thats only an issue if you get an underdrive crank pulley but that holds true to under driving any part, and its even worse if you have underdriven crank, alt, and ps probably have to go at over 4500rpms to reach the alternators peak power good fun there ^_^

 

YeuEmMaiMai: This isn't exactly correct. I agree that by slowing down the compressor you decrease the capacity of the AC system, but the pressure won't change. The capacity will be limited because the maximum flow of refrigerant will be less, however the system pressure is limited by an orifice valve and the compressor has an internal bypass. I have the UR set and have no problems. On the hottest days, the air will blow cool at a stoplight but get fully cold once I start moving. That's the only negative effect and to me, it's barely noticable.

As far as underdriving the alternator, I'm not a huge fan of dumping all kinds of inefficient power into a system. I have a Phoenix Gold Tantrum 75Wx4 RMS and a headunit right now. I also had an Alpine sub amp that died; it was pulling about 250W. Since the headunit amp is not hooked up to speakers, it barely uses any power. When I had the sub amp, I also had a 1F capacitor. This system never had any issues with the underdriven alternator.

 

i consider myself fairly knowledgeable about car stuff, but all of this is like greek to me.

Just so i get this strait in my head, if i have a 1700W system i shouldnt get a pully system that goes light on the alternator pully. But if i dont care about the ac blowing, or never use the AC even in the summer, i can go smaller on the ac pully?

Is any of that right? Its not like i plan doing this anytime soon. I just want to make sure that i understand all of this.

 

If you have a 1700W system, you probably have a high output alternator, second battery, isolation circuit and 2 Farads worth of capacitors. For this type of system, I wouldn't underdrive the alt. Somone mentioned that UR states that their underdrive system is good up to 600 Watts on the stereo.

As far as the AC goes, underdriving a bit will cause very little change during normal weather. It won't cool quite as much when it's 98 and humid outside.

I haven't heard of any problems with the AEM or Unorthodox Racing setups and for pre-made, they are your choices. The biggest gain is from lightening the crank pulley, so if you are concerned then go with the UR lightened only crank. If you want to underdrive accessories individually, the AEM pulleys are underdriven from the device (alt. or AC). The AC pulley is so small that there isn't much potential for gains there.

I have the underdriven UR 3-pulley kit and have had no problems. As mentioned, my system has never exceeded 600W-RMS and had a capacitor when the sub amp worked.