I went ahead and put on the AP Pulley today, and it took a while to get the crank bolts on and off, but otherwise went ok. Belts were tightened properly the first time around and all. Car shuddered a bit at first, and threw a CEL, but after resetting the ECU with the AP and driving around a little it seems fine. It feels like the car is more responsive in the lower revs, with a little more punch up top. Also seems to have smoothed out the AC cycling a bit.

I went ahead and data logged the voltage before and after, at idle and cruise, to try and clarify what exactly under-driving the alternator does to the voltage. Basically, in stock trim w/ nav, it had no effect on voltage cruising, or at idle with nothing extra turned on. Where I did see a drop in voltage compared to stock was when idling with everything turned on. Normally the voltage would sit around 13.8-13.9 for me, but with the pulley installed I now see 12.3-12.4 in this scenario. So there isn't any wiggle room left for aftermarket stereos, etc, at that point. There wasn't any flickering or weird happenings at this voltage for me in stock form though. Otherwise, I didn't notice any difference in the AC, but it was 75F outside so I don't think I will be able to tell until it's warmer.

I've attached my voltage graphs below.

 

This is a good read for me cuz mine is in the mail
So is there anyway to fix the voltage well idling?
Thanks,
-Gil

 

I think you may have gotten you lines mixed up on your graph as graph #2 doesn't reflect what your talking about.

 

yeah, don't underdrive your source of power

or increase your idle speed

 

AP pulley is just the crank, should not effect voltage. I've had mine for more than a year, no issues........no voltage change...fyi

 

The alternator is driven off of the crank, of course it will affect it

 

yeah alt is ran off crank pulley sochanging sizes will slow or speed up the alternator motion!

 

So when I get my Cobb AP and if I adj the idle speed will that fix it?
I'm going to PM Jeff...

 

Fixed it, sorry about that.

I'm not sure if raising the idle a little would make any difference. I mean I guess if you raised it 15-20%, but it hasn't caused me any issues being in the mid-to-upper 12s in those conditions.

 

From what I was told it should but I'm going to ask MM just to be on the safe side. I'll post what new may come, hell I told hime to chime in and post so lets see whats up.

 

my pulley kit has the most underdriven crank pulley, but they also supply a smaller than stock sized alt pulley, so the alt isn't underdriven. best of both worlds, and if you decide you want to underdrive the alt too, just install the oem pulley there.