underdrive pullys to me? I've been reading somethings about them but don't understand. What excatly to they do? What things need to be done to put them on (can you put them on a bone stock car)? What are some good types? And are they worth it?
Can someone explain....
- Thread starter Must-Be-A-Stang
- Start date
-
Sponsors (?)
Funanin
Founding Member
Well it looks like u like BBK, so i would say go with BBK if u want to buy a set.
What they do is basically slow down the accessories (alternator, air conditioner compressor, power steering pump, water pump) so the engine has less "drag" when trying to accelerate. Basically its like when u have ur A/C on and ur car runs slower thats the opposite of what underdrive pulleys do.
What they do is basically slow down the accessories (alternator, air conditioner compressor, power steering pump, water pump) so the engine has less "drag" when trying to accelerate. Basically its like when u have ur A/C on and ur car runs slower thats the opposite of what underdrive pulleys do.
CManT1914
New Member
Yea the pulleys for the alternator and water pump are smaller? than stock, so they make those accessories spin slower. Then the crank pulley is bigger? so it takes the power that was being used to spin those larger pullies and applies it to the crank instead. Something like that. 
Funanin
Founding Member
CManT1914 said:Yea the pulleys for the alternator and water pump are smaller? than stock, so they make those accessories spin slower. Then the crank pulley is bigger? so it takes the power that was being used to spin those larger pullies and applies it to the crank instead. Something like that.
Other way around... Accessory pulleys are bigger, crank pulley is smaller.
CManT1914
New Member
FiveLtrRiceEatr
New Member
Funanin said:
yep thats correct, basically it gives you some of you hp you lose when the AC is running.
So if I decide to run under drive pullys it would be a wise chioce to take out my stereo stuff? My car already drains a little bit and have some trouble with alt pushing enough. ( I think I have a drain or bad postive starter to battery cable ) I got a 100+ alt (cant remember what it was excatly) Maybe, these wouldnt be a wise choice?
Thanks guys for filling me in.
Thanks guys for filling me in.
89MustangGX
I have nothing productive to add!
manpowermustang said:
I didn't even know they produced underdrive pullies nor have I seen these test results. Where did this come from?
Funanin
Founding Member
89MustangGX said:
Im with him. Never heard of aeromotive pullies, only fuel stuff.
Also, if u have a high output stereo, leave your stock alternator pulley on or get a smaller one so it spins faster. You will only suffer like 1 or 2 hp out of the proposed 10-15.
as said people often have idle level charging issues with the addition of pulleys (depends on the pulleys used, idle setting, set up, etc).
i would add that most of the quantitative gains come at higher revs. if one mainly drives at slow revs on the street, im not sure it is the wisest idea.
i would add that most of the quantitative gains come at higher revs. if one mainly drives at slow revs on the street, im not sure it is the wisest idea.
PNY PWR
New Member
I've had them in the past. Not the greatest mod IMO. I'd spend the money elsewhere.
You can have cooling and charging issues with UD pulleys, not worth the minimal gain.
You can have cooling and charging issues with UD pulleys, not worth the minimal gain.
as i indicated, possible problems vary car to car. some have no issues, other have some issues. IIRC, Adam has had no issues, for instance (as Intrcptr said also). one can try them (if you really want to) and if it sucks, mod the pulley (ratios, etc) or go back to stock.
good luck.
good luck.
Michael Yount
Mustang Master
Some misinformation in the thread - the drive pulley (on the crank) on underdrives is smaller than stock. A smaller drive pulley slows down all the driven accessories. The driven pulleys - usually an alternator and water pump pulley on most kits - are almost always SMALLER than stock - to slightly speed those two accessories back up. A smaller driven pulley speeds the accessory up. A bigger driven pulley slows the accessory down. Most kits want to slow down the a/c, p/s, and air pump. The smaller pulley on the crank does that. But they don't want to slow down the alternator and the water pump as much to avoid charging and cooling issues. So they supply smaller pulleys for those to speed those two accessories back up a bit - not to stock levels, but not as slow as the other accessories.
The speed change is directly proportional to the diameter of the pulleys. So measure your new pulleys and the stockers and you'll know exactly how they're gonna impact accessory speeds. Manufacturers should be able to tell you exactly what their pulleys are going to do to each accessory. FRPP says that their u/d's slow the water pump by 22% and the alternator by 11%. They don't mention how much slower everything else will be - but by comparing the crank pulley diameter to the stocker, you can calculate it the % reduction.
If it's a street car (stock mechanical fan) with a-c in a hot climate, and you use the air in heavy traffic during the summer, you may have cooling issues. If you have the stock 65A alternator under the same circumstances you may have low speed charging issues. On mine, I had charging, cooling and a squealing power steering pump under low speed, summer conditions. Putting the stockers back on solved it.
The speed change is directly proportional to the diameter of the pulleys. So measure your new pulleys and the stockers and you'll know exactly how they're gonna impact accessory speeds. Manufacturers should be able to tell you exactly what their pulleys are going to do to each accessory. FRPP says that their u/d's slow the water pump by 22% and the alternator by 11%. They don't mention how much slower everything else will be - but by comparing the crank pulley diameter to the stocker, you can calculate it the % reduction.
If it's a street car (stock mechanical fan) with a-c in a hot climate, and you use the air in heavy traffic during the summer, you may have cooling issues. If you have the stock 65A alternator under the same circumstances you may have low speed charging issues. On mine, I had charging, cooling and a squealing power steering pump under low speed, summer conditions. Putting the stockers back on solved it.
PNY PWR
New Member
Let's come up with some $100 or so mods better than UD pulleys....I'll start off with a cold air kit.
Funanin
Founding Member
