Guys, my 70 skylark with the March aluminum pulleys isn't charging very well. Its killed batteries twice this summer since I've had them on. Any way around this? I like the pulleys and don't want to take them off. Of course getting stuck bites the big one. If I go to a higher amp alternator maybe? It doesn't charge much under 1500 rpm. I have electric fans and an MSD in the car so I'm sure thats not helping any. Thanks Bob
What is your voltage at idle? What is your voltage when you are cruising? How do you know you don't have some other problem like a bad battery, a slow discharge, etc.? Do you have a bad voltage regulator? Pulleys are only 1 component in the charging equation. -Bob Cunningham
If your running a stock alternater (especially an old one) your not gonna be charging much (if any) at idle with the underdrive pulleys, simply moving to a higher output alt. is not going to solve the problem either, it may actually make it worse as some of the higher output units don't get going until they reach higher rpm. You can have your alt rebuilt (by a quality shop) and tell them what your pulley ratios are and you idle rpm so that they can taylor it to your application, or you can go with a CS130 one wire alt which is stronger at lower rpms than the old 10s and 10si's. I run the underdrive crank and water pump pulleys but run an overdrive alt pulley (and a CS130 alt.) this works very well, I get some good underdrive to the power steering and water pump, I run electric fans so lower water pump speed doesn't affect my cooling. The overdrive alt pulley in conjuction with the underdrive crank pulley produces an almost stock ratio, basically a wash.
survey says.... i firmly agree with len.the cs-130 alt will charge at least 60%of rated output at 1200 rpm.only way to go and bolts right in:TU:
CS130 questions Len, can you tell me what application these alt's came in and what years? Or where's a good place to pick one up if not from a local parts store? I also have a question on where you picked up the overdrive alt pulley. Thanks!
Jeff, The CS130 is a later model GM Alt, get with Jamie (post above your last) and he should be able to help you out. I had a friend that had one in his garage, otherwise I would have got Jamie to hook me up. My dual belt overdrive pulley came off an early 80's S-10 pickup, cost me $3 at a U-Pick yard.
Know how much "horsepower" is "saved" with underdrive pulleys? NONE. The average 100 ampere alternator, with the smallest diameter pulley that can be had, uses LESS THAN ONE HORSEPOWER TO OPERATE. Even Pro-Stock racers are now getting into running alternators. Now, as stated here, nothing is going to help a wounded or dying alternator, but underdrive alternator pulleys are not an answer to anything but a person just begging for more problems.
Yep, definately agree with Dave, underdriving an alternator is a mistake. If you want the gains of underdrive pulleys reserve them for the water pump and the power steering pump, and only underdrive the water pump if you have a rock solid cooling system and/or running electric fans, the reduced belt driven fan speed on a suspect cooling system can be enough to cause you some serious cooling problems.
Bob, I've had something similar happen... but on an older alternator. I had the wrong pulley for the 455 (The alternator came from a pontiac 301) and it would only charge if I let the RPM come up at idle. I changed the alternator itself to a rebuilt unit very similar to what lcac_man describes (same pulley though) and it corrected the problem.
