Sorry to tweak your buttons Nonsequitur. I was just trying to add some info in the use of underdrive pulleys. Forums are for open discussion, and yes, they will sometimes drift in a different dirrection, but all the information in this thread pertained to the using of underdrive pulleys. If the original poster isn't interested in it, then they can pass over it. Don't try and be so controlling and let's keep this place a fun and entertaining place to discuss our vehicles. Good day.

 

Yep, Yep and yep to this post

BTW, Wittom makes some excellent points in his post as well and I agree with him

I would also add that I too have a prefferance to Magnaflow mufflers. Iwould do a CAT back instead of headers (unless I was serious about getting the SuperCharger on inconjuntion.

 

I could be wrong, guys, but I believe the HP required to turn your alternator increases as the electrical load increases. If that is true (and someone will correct me if it isn't), then a high output sound system will use some additional horsepower. How much, I don't know.

 

GlenFord, you are correct. The more electrical load the more HP it takes to power it. In a perfect world 1000 watts takes 1.34 HP. and btw the alternators only put out 130 amps when they are required to so. It all depends on how much load you have installed. The more load the more amps the alt. puts out. ie. on a stock setup you alternator never puts out its rated output of 130 amps.
Jes

 

I have to disagree. On occasion I have seen stock and rebuilt units both put out over it's rated capacity. In fact my truck on a cold day with a warm engine tested at 138 amps and 15.2 at 2100RPM. Several months later I was cusious on how it was doing and it produced only 14.92 volts and 123.8 amps, with only the radio on but the air temp was much higher but this time with a cool engine. What I am saying is that it doesn't always make perfect since but point being is that they do sometimes put out more than they are supposed too. I'm not an expert on that matter and will never claim to be. I just know what I see everyday selling parts. 99% of the time if they are good they put out within 20 amps of the rating.

 

I think the tb spacer is a great investment. I just put one on my truck last week and i can tell alot of diffrence with torque its good for the cost since its less than a hundred bucks.

 

NaviMan, rocketir, & KYFordFreak:

First, NaviMan:

I was wrong about a "high" powered sound system not being affected by underdrive pullys. When it comes to sounds systems I am "lame" I have a stock system which is fine for me. I was not thinking about the "big time" amps etc. So I stand corrected on my ealier post. Underdrive pulleys "could" have an effect on your electrical system depending on the amp requirement.

rocketir:

I can tell you from working with generators, alternators, motors etc. that when it comes to your alternator putting out more amps it does "not" require more horsepower from the engine. You are correct that the alternator does not put out 130amps just running the motor. It does however have the capibility to put out 130 amps if there is a requirement (load) with the motor just running at idle. I should have made myself clearer when I stated the alternator could put out 130amps with the engine at idle of which it can if there is a demand for it (load).

One thing to note is that all alternators are not the same. Mine my only put out 130amps max, while another same design will put out 140amps max. It is a rating only. It all depends on the internal motor windings, brushes etc. As with our motors and generators we produce they have to meet the stated requirement as a min. so in other words testing at a temp of 78 degrees F it must put out at least 130amps. I am sure there is a max rating as well but alternators, generators are not listed with that only min. output.

There are factors that will affect the amp output. As I stated they are tested at a certain temp. so as KYFordFreak pointed out if it is a hot day, or hot and humid it will put out less amps. This is due to the motor windings being at a higher temperature thus increasing the winding resistance which in turn reduces amp output.

KYFordFreak:

You are correct as well as far as what you say for testing your alternator. When you tested it what ever piece of equipment you used puts a load on the alternator which will then be able to tell you the amp output. But as rocketir stated unless there is a need (load requirement, i.e. A/C, lights, high powered sound system) it will not put out its max amp output.

To wrap it up:

1. When there is an increase demand for more amps, your alternator will put it out but will not require any more horsepowere from the engine to do so. Its already there waiting to be used when needed. (Its a long explaination as to why it dont take more engine horsepower for higher amp requirements)
To make it short, the alternator has motor windings, along with a rotor that has windings. The rotor is built into the motor with bearings. The engine is only rotating the rotor through the pulley. The only reason the engine would have to put out more horsepower is say if the bearings were draging due to being bad. Even if that were true it would be very low, less then .5 to 1 hp if that. First you would never notice, second before it did effect anything it would be so load you would know you had bad bearings.

2. When the engine is at idle with min. load requirements the alternator will not be putting out its max. of 130amps. If there is enough load requirement for 130amps, it will put out at engine idle.

3. I was originally wrong about underdrive pullys "maybe" not effecting the electrical system due to high current drawing amps found in high powered sound systems. However it will not affect a stock sound system.

 

MIne were always tested on a Bear Arbst tester brand found at most Advance Autos. It is usually fairly accurate and simple to do, even for a dummy like me.

The only thing I can remember that was on when I tested mine was maybe the heater and radio. That amperage was not at idle, that was taken at about 2100 RPM. Idle amperage would be much lower, less than half of that 130amps. Your alt will not usually produce peak amps untill it reachs about 1800-2200 RPM. I am not for sure if it would produce peak amps at engine idle speed. I seems to me if the electrical demand at idle was too great it simply start to discharge the battery. Many times when I have tried to test cars with a bad ALT that wasn't producing enough amperage, the car would die mid-test at the point where you rev it to about 2 grand, as the amperage draw from the tester took more than the ALT could put out. So it was basically pulling the juice that's need to keep the engine running.
I'm not an automotive electrical wizard, just stating what I have personally observed.

 

hummmm, sounds to me like it's not always a good idea to slow down the speed the accessories turn via pulley swap. In addition to the demands placed on the alt by hi current amps, lighting systems, etc. you may also consider that the cooling system could have problems as well if you are stuck in 90+ degree bumber to bumber traffic.

As for the $50+ dollar paper weight 'throttle spacer', they are only good for two things. The first I already noted, the second is adding a loud whistle noise to your intake system. Many, many have posted that you will not get any HP or MPG increase with these cute little CNC machined paper weights

 

I gotta disagree with you on this. Conservation of energy rule applies here. The only way that the alt. wil put out more amps and not demand more HP will be if the voltage dropped, but that's not going to happen.
by defination 1hp = 746 watts. where watts = amps * voltage.
if you increase the total amps demanded, you have to supply more hp to rotate the alt. the alt is not like a battery or some other stored energy device. It just converts mechanical energy ( the rotating crankshaft ) to electrical energy.
Jes

 

Hmmm,

I'll have to think about this one. If the alternator pulley is free wheeling regardless of the amperage load, then how does this affect the hosepower? The alternator should be turning the same whether you are running the stereo or not. By putting more demand on the alternator by cranking on the stereo doesn't increase the resistance of the alternator, it just forces the electrical system to borrow more amps from the alternator to keep from digging into the reserve capacity of the battery and eventually running the battery down. That's why alternators have regulators. The regulator adjusts the voltage to keep up with the demand of the electrical system. If the alternator needs to put out more amps, it doesn't speed up the engine to make up for the draw from the stereo system.

On the other hand, the AC will decrease horsepower when it is on, because when the compressor kicks on it offers more resistance to the engine which would make the engine have to work harder. When the AC is off, then the pulley becomes free wheeling again and thus more horsepower.

Does this make sense?

 

I am sorry if I am unclear in my writing but these guys say it better.
http://cartalk.cars.com/Columns/Arch...01/May/07.html

Jes.

 

Who can argue with Tom and Ray.

But I'm still not convinced their theory is totally correct. The alternator spins the same whether there is a large demand for electrical power or not. What would make the alternator harder to spin when a heavier electrical load is put on it? There is no internal clutch that is being activated like an AC compressor. An alternator has an amp rating and once that amp rating is exceeded it then draws from the battery. I guess I'll have to go put a heavy load to my charging system and see if the tach drops in rpm's. I know the more accessories you have on it will make the power windows possibly roll up and down slower, but I don't recall the rpm's changing. Oh well, maybe somebody that is an automotice electrical technician can shed some more light on this. Even if it did draw some horsepower, it's got to be pretty negligible, and you wouldn't even notice it.

 

rocketir:

BENF, BEMF, BEMF, sometimes I really **** myself off. Here we go again. As far as the alternator you are right. BEMF (back electrical magnetic force) this happens as the current draw on the alternator windings increase. What happens is it makes the alternator rotor windings become a "stronger" magnet. This stronger magnet cause the BEMF within the alternator which in turn causes more "motion" (or rotation) resistance to the rotor which in turns makes it harder to turn. If something is harder to turn then of course it takes more force (hp) to turn it at the same speed. I have been away from alternators and generators for so long I forget the simple things. I work mostly with elctrical motors and motor generator sets. With the motors we are testing No-load speeds, and then of course Full-Load speeds with a set torque, speed torque curves etc. Still not an excuse for posting BS information so please accept my aplogy.

Someone mentioned that the alternator does not put out full load until around 2,000rpm. That is probabely correct. I am not sure where the full load amps are rated at. I had suspected that it would put out at engine idle due to the fact if you are drawing close to full amps say with accessiores etc that to "not" be able to put out full load amps is a very poor engineering design. Let's assume you are in need of 100amps at idle but the alternator only puts out 80amps at idle. Now your battery is called on to supply the other 20amps. This will only last so long until the battery is completely dead. If your lucky and the battery dont completely drain then it will need a much bigger charge then just a trickle charge. Anytime you need more then a slow trickle charge it wears the cells in the battery out so now you will have premature failure of the battery, which means buying more batterys like I said poor engineering design.

 

I hate to bust in to the tech talk as I have little alternator experiance. I do know from experiance that it DOES take more power to turn these things fast and by increasing the size of the pulley you are decreasing the speed of rotation which lowers the paristitic HP loss. (have you ever 'hooked up' a generator to a stationary bike?) It also reduces alternator output at a given RPM which, if you have high current demand electrical devices, can cause problems for them. I think this IS the issue as it relates to current draw vs power pulley (electrical device performance)

Likewise slowing down the water pump can 'free up' a small pecentage of the motors HP, but again the compromises come into play, and so on the power steering pump, the a/c compressor, etc.

I would like to think the power pully MOD has now been covered and would like to see some of his other MOD options be addressed now as I am contemplating some of them myself (selfish aren't I)