I ended up with a crank underdrive pulley, but not the alternator or water pump pulley. Would it be worth changing just the crank pulley?

It does look better than the stock pulley and weighs less. I dont think it will make much of a difference. What do you guys think.

It will help. A full set claims 10-15hp upgrade over stock pullys so...7-8hp? You'll have to get a new belt too I believe because of the size difference.

if this is your daily driver, you're may run into charging issues with the alternator and possibly a hotter running setup since you've slowed down the rotation of everything else. While you may pick up some lost hp, you may be hurting a few other things in the process. If its just a weekend warrior, go for it.

I did this and the engine free rev'd better. Not sure how much if any power i gained, track didnt show much, half tenth or so but i did experience charging issues with no alternator pulley.

AFter i went to the smaller alternator pulley i had no problems

agree! i have the march underdrive pulley on my crank, way lighter/smaller than the stock. It was a 2 peice set (crank/alt) but i found that the alt pulley was too large and it was wrong lol it was a 6 rib belt when the crank was a 5rib belt. I kept the crank and used it but i found a smaller than stock alt pulley and it works fine, charging isnt bad unless im at a stop light with my lights on and my radio etc even then its still like 12V...

Well its not a DD, just on occasions and to the track and back.

I might try it and see what happens.

I am running a a/c delete pulley and no smog pump. I will have to measure for new belt.

The purpose of the alternator pulleys in those kits is to make the alternator spin faster to make up for the loss in speed from the smaller crank pulley. So you're going to make more HP with just the crank pulley than with both pieces, but less charging capability at the same time. I dont know what the water pump pulleys are so I cant comment but if they're smaller than stock then its the same story there.

Same here. Scored an underdrive crank pulley at a swap meet for peanuts. Then took my alt pulley with me to the junk yard and went through this bin of altenators until I found one that had the same inner shaft size and was smaller in diameter. Took a WHILE but I found one. Junk yard operator thought I as crazy out there with a mic, measuring all these pulleys.

Ok guys, on the topic of changing the alternator pulley. What if I keep the stock crank pulley and changed the alternator pulley to spin faster. Would this be a good idea?

This is just in theory, would it help a stock charging system?

Im not having any charging problems, but it might be a solution for someone else. Whats your thoughts?

I think there would be a point where extra spin speed on the alternator would not produce anymore current/amps/etc. there is a speed in which the alternator needs to spin to charge the battery and run the motor at idle and the ratio between crank pulley size and alternator pulley size achieves this. Underdrives are smaller in diameter but maintain that ratio to have good charging at idle. If you go faster i dont think it will help since the alternator can only put out so much power.

I'd go with an aluminum crank pulley and the alternator pulley to free up rotating mass and let that engine free rev faster. It works and does give a small power gain

Thanks Orr, I thought the the stock alternator would have its limits.