I saw that underdrive pulleys for my vette ('89) can be had as a single crank pulley or a 2 pulley kit, crank and alternator. I know the crank pulley is smaller so it slows everything else down. My question is: Is the alternator pulley smaller than stock to speed it back up to normal, or is it larger than stock to slow the alternator down even more? If it is larger than stock I will not buy the kit that includes it because I don't want my alternator slown down any more than the crank underdrive pulley is already going to slow it down. At least I don't think I do, but maybe now that I'm idling at 850 rpms it won't matter. I have a big sub that drains the battery quickly and I use it alot so I need to keep the alternator turning! Suggestions?

Nobody has underdrive pulleys?

I got 'em

I notice a difference with throttle response. THe engine wants to spool up faster. Its noticeable.

The speed at which the alt turns is a problem for those that do alot of daily driving. The battery will have to hold up the elec system when the engine is below 1800 RPM. THat makes driving with A/C or lights on a real drain on battery life.

As for HP gains...... maybe a few. My butt-o-meter says its noticeable.

Thanks for the reply. So, you bought the single crank pulley or the 2 pulley kit? I'm trying to figure out if the alternator pulley that comes with the 2 pulley kit is bigger or smaller than the stock alternator pulley.

It's smaller. By putting a smaller crank pulley on everything slows down just like you know it to. In order to speed the alt back up you have to put a smaller pulley on it in order to bring its ratio with the crank pulley back in line.

Thanks, that is what I needed to know. If I buy underdrive pulleys then I'll buy the 2 pulley kit. I hope my water pump still spins fast enough tho, seeing as how it is going to slow down.

since you are an auto, I'd either not buy the UD pulley or get the two pulley kit. Autos idle lower than sticks when sitting at a stop light.

The water pump will be fine if you radiator and fans are working as they should.

For what it's worth, I wouldn't spend the money on the pulleys. It's just not worth it I think. There are better items to spend your money on.

Thanks for the info. With my cam I have my idle at about 850 to 875 and I like it there. With the higher stall converter it is hardly noticable that it is higher than stock. I hate to say this but performance wise I am running out of things to spend money on (until I can afford a forged bottom end and can spray a 300 shot instead of a 125 shot). I need to save for part breakage so I don't know if I'm going to spring for pulleys or not tho. I've been told by some that underdrive pulleys will pick up .1 or .2 in the 1/4 mile, others say no gain at all.