Well, my FD alternator is in. I have 4 gauge wiring connecting the alternator to the battery. Dual belt pulley.

14.7 volts with nothing on. Once I turn all my stuff on, lights, sub, etc. I am dropping down to around 13.5 ish. As soon as I hit my brakes, at idle, I am dropping to 12V. Lights dim, etc. Now, I am idling smoothly at 650 RPM. I am going to be turning it up, but need a new o-ring for the idle control screw.

Would idling 100 RPM less cause that dramatic of a drop? I thought bumping it from 65A to 100A would cure the problem of the lights dimming as soon as I hit the brakes.

Suggestions?

 

Ditch POS underdrive pulley

 

It doesn't look underdriven.

Stock pulleys on the engine, and the pulley on the alternator is the same size as the stock FD one.

 

Have you ever seen the stock FD crank pulley?

 

No. Smaller? Bigger?

 

Question: This is what happens at idle? What does the voltage do at higher rpms?


The crank pulley to alternator pulley diameter ratio on an FC is 4.5:2.5 or reduced to 1.8:1. Check that ratio on the FD crank. Compare it to what you have on your FC.

 

It sounds normal to me.


-Ted

 

Thanks guys!

 

I've been told that the "normal" reduction is 3:1 which I believe is about what the FD runs. I'm going to pull some measurements when I get the time. IIRC, the FC crank pulley is smaller than the FD pulley so if the alt pulley is the same size - YOU ARE UNDERDRIVING IT and from what Ive been told by some pros, the alt amperage will dramatically decrease under "normal" idle speeds. If your voltage drops into the 12's you are basically running off battery power