Then you need this little guy I picked up. Aeromotive alternator overdrive pulley part #21102. Made of billet aluminum, they also make a v-belt version.



I put the BBK 1598 underdrive pulley set on my car. I read all the usual complaints about idle charging quality going straight to hell. I first ran with the alternator underdrive that came with the kit. I would not recommend this pulley for...Almost any scenario. As a street car, this pulley is an extremely BAD decision. Idle charging is... Wait, what idle charging? At idle especially sitting in traffic on a hot, humid and rainy day with the wipers going, headlights on and A/C blowing the alternator did not charge at all and voltage would drop to about 10.5v - 11v and start pulling from the battery. I literally had to put the car in neutral and rev the engine up until traffic got flowing again. Also when the battery starts taking a hit the alternator has difficulty charging it back up at anything under 2500rpm. As a track car... Well, if you have anything serious enough to be predominantly geared towards the track you are generally not going to be wasting your time on something as trivial as underdriving the alternator. Not to mention you will be eating your battery in the staging lanes. Any use that places the engine at low-mid to high RPM almost all the time it would be OK for, however. Out comes the impact gun...

Next up was the stock pulley. This was noticeably better at idle charging and wouldn't have been a bad choice for everyday driving with light to moderate traffic however I still wouldn't trust it in the above scenario.

Lastly, I did a search for an alternator overdrive pulley and came up with two part #s:

Aeromotive 21102 is a 6 groove pulley that overdrives the alternator by 32% and can be used with the 6 groove serpentine system found on later year thirdgens or the early style 5 groove serpentine/v-belt setup like I have on my car (If 5 groove just seat the belt biased towards the alternator with the sixth groove at the very front of the pulley not being used).

Aeromotive 21103 is a v-belt pulley that overdrives the alternator by 50%.

Comparison in size of the underdrive pulley, stock pulley and the aeromotive overdrive pulley:



After installing the overdrive pulley, I finally have good idle charging once again. At a dead idle with the music going hard (everything amped with two 12s in the back) and the blower motor on high I had a steady 14+ volts. In the same conditions with all headlights on, wipers on high and the rear defroster turned on voltage dipped a bit under 13v but still not low enough to put a hurt on the battery. I would highly recommend these pullies to anyone thinking about installing an underdrive setup.

Keep in mind these readings were taken by an autometer volt gauge inside the car. I didn't bother to get out my multimeter but the readings directly at the alternator post and battery terminals would have most likely been a little higher because with all those heavy loads turned on at once I would think the stock wiring that supplies current to everything at the starter would begin to become a restriction.


ONE thing to keep in mind especially if you have a cammed motor that likes to spin high. You need to make sure you are not spinning your alternator too fast. The alternator manufacturer should be able to provide you with the rated redline of your alt. You need to measure the diameter of your crank pulley and then divide it by the diameter of your alternator pulley to get your pulley ratio. You then multiply this number x engine RPM to figure out your alternator RPM. Spinning the alternator too high can cause the fan blades to flex to the breaking point which will really ruin your day when they fly off and dent/come through your hood or break something else under it.

http://www.powermastermotorsports.co...r_pulleys.html

As an example we divide the diameter of my crank pulley at 5.5" by the diameter of my alternator pulley at 1.93" to come up with a ratio of 2.84. So theoretically I should be able to spin my engine to 6400rpm before exceeding the 18,000rpm redline of my alternator. The poo-poo cam motor in my car now could only dream of going that high and the new engine I have planned will be spun to within a few hundred RPM of that number so it looks like this pulley is just right for me.

At a 650rpm idle I am also spinning the alternator at 1846rpm. A little shy of its 97 amp at 2400rpm rated idle charging but I should still be putting out about what the stock alternator rated at 70amps was good for at highway speed. This also means that I have the full 142 amp at 7500rpm rated output by roughly 2640 engine RPM. For what I demand from the car and with 3.73s at highway speed, this should never be a problem. Also, this is only considering the stock idle rate of a thirdgen. You can get creative to boost idle output a bit. For example, by increasing the engine idle speed by only 100 to 750rpm, we increase the idle RPM of the alternator to 2130rpm. At an 850rpm engine idle, definitely not as tame as stock but still manageable, we will reach 2414 alternator RPM which would give us the full 97 amps at 2400rpm idle rating supplied by powermaster.

I will also supply numbers for the other two pullies pictured:

At 2.45" with a 2.24 ratio, the stock pulley with a 650rpm idle would be spinning the alternator at 1456rpm. The real problem though is that it wouldn't have reached the full rated output of the alternator until 3348 engine rpm. Unless you have a 3 speed auto and do alot of highway driving, you probably won't be getting the rated output of your alternator.

At a mammoth 3" with a 1.83 ratio, the alternator underdrive pulley with a 650rpm idle was only spinning my alternator at 1189rpm. And with this pulley included with the underdrive set I would not have reached the alternator's full 142 amp rated output until a whopping 4000 ENGINE rpm. We also would not have achieved the rated idle output until 1311 engine RPM. When powermaster said circletrack racing only, they weren't kidding.

 

Yeah I've had em come through my hood before... ruined a PERFECT 69 Chevelle SS hood that way once...

 

I would be a little upset about a fan blade coming through my 3" fiberglass cervini.

I suppose for high RPM drag motors the underdrive pulley could come in handy and you'd be able to spin your engine to 7500rpm while the alternator whirls at a cool 13725rpm.

 

Great write-up. Thanks for doing that.

Quick question.... how did you make that upper alternator bracket fit like that? I've got the same bracket and it definitely fits on the OUTSIDE edge of the alternator mounting ear, not on the inside. I know the stock 86-87 v-belt + serp belt systems are a bit oddball compared to either an earlier v-belt-only system or an 88-up "true" serpentine system, but I didn't think they were THAT oddball. Did you not get the spacer that goes with the bracket to space it out slightly down at the water pump attachment point?

 

The bracket I grabbed out of a local speed shop and there was no spacer included that I remember. It does look a bit odd and I suppose I could make the correct spacer to place it on the ouside of the alternator casing without it hitting the waterpump pulley but it's never a bother enough for me to take the waterpump pulley off to get at that bolt.

 

Wow, that's odd. I just went out and looked at mine again- no spacer. Sorry. I recall there being one, but apparently I didn't need it. Still fits on the outside of the mounting ear! Other than the thickness of the the lower mounting bracket, the bolt location is identical between the upper and lower brackets- they are on the same "plane" other than the extra ~1/8" thickness of the lower bracket.

I'm guessing we don't have the same upper bracket, other than visual similarities.

 

This was cool info...thanks for taking the time to write up n post....so which of the two did you go with

 

Not quite. At least in my picture.

If you look closely you can see that the two mounting holes for the lower bracket are right at the front of the waterpump while the top is recessed back a bit. Maybe it's just something weird Weiand did with their pumps.

BTW, this is why you don't paint aluminum with clearcoat. It always ends up turning yellow

 

I'm sticking with the overdrive.

 

That looks about the same size as my CV Products pulley

 

So you under-drove the crankshaft and overdrove the alternator ?
Means you could have left the stock pulleys and accomplished the same thing.

The biggest scam in the world are these under-drive pulleys. They run down the battery, make the car run hotter, and will not gain much "free HP"

BUT they look nice! and that is the tempting part.

You want some bling you can get a set aftermarket stock size pulleys and avoid all the headaches with under drive / etc. . because the "power gains" are minimal.

I am speaking from experience on this one. I had MARCH under-drive pulleys on my 305... I used them on the 383 because they were free and I already bought the overdrive pulley for the alternator.

All that went to scrap pile.. the performance gains are negligible.

 

Look, man, I have been more than patient with you. I am getting sick and tired of you harassing me in all of my threads stating the obvious. Then when someone calls you out for being an a$$ to everyone you immediately start getting abusive and telling everyone how much they have to learn.

Everyone knows underdrive pullies free up 5HP at the most and are as trivial as switching to an electric waterpump.

You troll this site searching for things you consider to be trivial or inferior. Then, when you post a bunch of redundant facts that everyone already knows and someone else gets technical to try and counter your opinion, you start calling everyone a bunch of young punks who "Don't know how to change a fuel pump". You bait people into arguments and I know that's exactly what you're trying to do here.

I KNOW a 305 is an inferior motor compared to the rest of the smallblocks and I KNOW that things such underdrive pullies are trivial. It's all part of going through the learning process as you just stated you have certainly done in the past. Let me experience these things for myself vs telling me how stupid I am!

**** off already and stop polluting the boards. You complain that this forum used to be full of "Real car guys". Guess what? You're not one of them.

 

Actually I am.

I also have MUCH THICKER SKIN than you.


Get over it. Mr. 1,950 posts.. I have been on this place for 11 years.. 206 posts...

who is the TROLL?!
Actually I think the term is "post *****" or is it "attention *****".

Look what I screwed up this week... help me fix it LOL !
I wanna take a turd motor and go fast, LOL !


I STILL OWN my car 20 years later. You were probably in diapers in 1993, LOL !!!!

This is all very comical to me

 

Thanks for the the confession. Makes my job so much easier.

 

Wow. Who knew fishing without a pole was so easy.

 

You have no race car, no timeslips, therefore no credibility.

Have you worked it out yet that constant childish abuse and always having the last word do not give you that credibility?


You are a just a show guy who makes poor choices, but your ego will not allow you to admit that, so to sleep better at night you run down other people and their superior products.

I feel sorry for you.

You deserve the pity of everyone on this site.

 

That's funny. I could have sworn I heard something just now.

Guess it was nothing...