Chris Stephens
New Member
Who in here has underdrive pulleys and can tell me the brand and measure them for me?
If you're just gonna reply, "wAsTe oF mOnEy, dOn'T bOThEr" (the answers I've gotten elsewhere so far), then please don't bother. I'm not looking at underdrive pulleys to gain .3 horsepowers, I have an actual use for them.
Currently I am having a problem blowing up alternators. Installed a new one on a Friday, it worked fine all the way to the AutoCross event, and then quit during my first run. Wiring checked out ok, but the alternator has plastic mangled inside and windings broken and touching the case. Wasn't that way before the event, but since it quit immediately after the first run, all I can figure is that I'm running them at too high of RPM.
After crunching the numbers, my 6.5" crank pulley and 2-1/8 (2.125)" alternator pulley gives me a 3:1 alternator to engine ratio. I spin to 7000 RPM, which is about 21,000 RPM at the alternator, and I get to 6000+ multiple times on fast courses like we've had recently.
From what I've read, the 3G alternators start charging at 2000 RPM (alternator), work best around 6000 RPM, and shouldn't be run over 15,000 RPM.
If I can find a set of underdrive pulleys that give me the right ratio for the crank and alternator, close to 2:1, I think I'll be golden. I idle at 1000 RPM, and cruise around 2500 RPM on the few occasions I street drive it. No "extras" in terms of power use, no sound system in the car or anything like that.
So...to the original question, can anyone tell me what brand and diameter underdrives they're running? Or recommend a larger alternator pulley, closer to 3", or a smaller crank pulley, etc, etc?
Thanks!
If you're just gonna reply, "wAsTe oF mOnEy, dOn'T bOThEr" (the answers I've gotten elsewhere so far), then please don't bother. I'm not looking at underdrive pulleys to gain .3 horsepowers, I have an actual use for them.
Currently I am having a problem blowing up alternators. Installed a new one on a Friday, it worked fine all the way to the AutoCross event, and then quit during my first run. Wiring checked out ok, but the alternator has plastic mangled inside and windings broken and touching the case. Wasn't that way before the event, but since it quit immediately after the first run, all I can figure is that I'm running them at too high of RPM.
After crunching the numbers, my 6.5" crank pulley and 2-1/8 (2.125)" alternator pulley gives me a 3:1 alternator to engine ratio. I spin to 7000 RPM, which is about 21,000 RPM at the alternator, and I get to 6000+ multiple times on fast courses like we've had recently.
From what I've read, the 3G alternators start charging at 2000 RPM (alternator), work best around 6000 RPM, and shouldn't be run over 15,000 RPM.
If I can find a set of underdrive pulleys that give me the right ratio for the crank and alternator, close to 2:1, I think I'll be golden. I idle at 1000 RPM, and cruise around 2500 RPM on the few occasions I street drive it. No "extras" in terms of power use, no sound system in the car or anything like that.
So...to the original question, can anyone tell me what brand and diameter underdrives they're running? Or recommend a larger alternator pulley, closer to 3", or a smaller crank pulley, etc, etc?
Thanks!
