Why is everyone here so damn sensitive? I have never put you down personally, I have only ever corrected what I believe to be incorrect information. There's a big difference. I can't even remember any other threads off hand, but in this one I was only trying to save you money. If I really wanted to put you down I'd just start calling you names. It'd require a lot less effort...

Output current is logarithmically proportional to alternator revs; simple as that. The S4 alternator is rated at 70A, but the FSM test says that 55A @ 2500-3000rpm is normal. So you obviously need more revs to reach to 70A max output. Slowing the alternator down will obviously lower the output current.

 

So the regulator only affects voltage output?



Santiago

PS- I'm constructing an excel sheet with the RP pully I have going from idle and then from 800rpms all the way up to 8k rpms showing the UD rpms. I'll post that up in a sec.

 

the other thread where i felt attacked was my weight reduction thread where you said how worthless removing some things were, or something along the lines of "let us know what happens when you have a flat and are stranded on the side of the road" when you said how stupid taking my spare tire out, even though i had already explained i have AAA... my point was that it seems like you attack ppl a lot for their ideas or things they want to do



now my next point... the whole reason behind underdriving the FD alt was not to correct the fact that my volts might be too high... since i have the fd alt already and no big stereo, i figured underdriving it would give me that tiny bit of extra HP while still being at stock level of alt power... now the way i was looking at this whole thing was that underdriving an alternator gives you a lil more power. I would never do the main pulley on a street car cuz i think thats dumb, but since i already have a more powerful alt that i really dont need the extra power of (its just nice sometimes at night with the lights, wipers, and heat on) then underdriving it would essentially give me the power without reducing my making my power output too low

 

I'm getting 15.5 off my honda accord with everything off (stereo, etc)

 

k here is a screen shot of that sheet:

 

That's why it's called a voltage regulator.
It's nice, but what does it prove?

If I really upset you that much then I'm really sorry. It was never my intention to attack you personally, only to express my negative opinion of going without a spare. Personally I'd much rather just change my own wheel in ten minutes than have to wait an hour for someone else to come and do it for me just for the sake of 30lb. I make a point of only saying what I think about peoples' ideas, not them personally. But I digress...
This is a common understanding, so don't take this personally.

Higher output alternators require more engine power to turn them. This is an unavoidable fact of life (the one where you get nothing for free). The FD alternator has an output 43% higher than the S4 one, and as a result it'll suck approximately that much more power from the engine. If you underdrive the alternator, you'll reduce both that power draw and the output by the underdrive percentage.

But if you do the maths, the power gain from underdriving a 100A alternator by 20% is ~0.5hp. You'll have trouble measuring the power gain at the wheels, let alone actually feeling it. Did you notice the tiny power loss from installing the FD alternator? No, because it was very small. The gain from underdriving it will be even smaller...

If the underdrive pulley is a 20% one, your FD alternator will end up about the same an 80A S5 one, and draw a tiny fraction of a hp more power from the engine than the stock S4 one. The numbers are so small IMO it's just not wasting time and money chasing them. Be happy with your new alternator's healthy capacity and spend the money on something you'll actually notice. And get that voltage regulator checked.

You too...

 

ah that makes sense then

 

So voltage and amperage are not tied together in output at all. Interesting. And I didn't say the graph was going to proove anything. Its there to show people what it is going to be doing to the alternator. If we can find out what rpm's the FD alt produces 100amps at we can figure out how bad or how much less amps it will crank out. I bought my FD alternator because my FC unit would cost ~50 dollars more to replace not because it cranks out more amps. Although I don't deny that it is great having that extra power output. My car handled the loads I put on it just fine with an FC alternator. Downgrading to FC alt amp output levels by underdriving the FD alt will only do two things: slow it down elongating its life span a little and decrease the drag on the engine from the alt perhaps(stressing "perhaps") gain a few ponies.


Santiago


PS- the graph was also for my own use as I have that particular pully.

 

I have an underdrive crank pulley, and an overdrive alternator pulley. These are not aftermarket pulleys, but pulleys off of cars at the junkyard. Charging system is fine, cooling system is fine. I believe they added alittle power, but no butt dyno proof, but its too little to tell even if it did.

 

After talking to silverrotor i just wanted to let everyone know that my alt is FINE. The intention of this thread was not that there was a voltage problem, it was for pure HP gain (ie the underdrive pulley). I have had no problems with the alternator or my powering system, it just came up in this thread for no reason. Everything is fine with it, no worries to anyone thinking of getting one from silverrotor its a great product and hes a great guy

 

The FSM disagrees with silverrotor. Anything over 14.7V is not fine. Just letting you know...

 

ugh....... you dont even know if im above 14.7.. The stock volt gauge (at most) will sit close to half way inbetween the 14 and 16v marks, so *around* 15, but the stock gauge isnt very accurate. Mind you that is the MOST it will ever read, it is usually about a quarter past the 14 mark. As silverrotor stated to me "If the Voltage Regulator was the culprit, 2 things would either happen. You'd either get very low output from It resulting In a very noticable rough Idle leading to a flat battery or with the other option, you'd get an unlimited amount of ampherage resulting In a popped Main Fuse." I have neither a rough idle or am i popping fuses, and ive been running this for a few months now

 

ok ok everyone calm down we are going to check the voltage tomorrow with my dmm.

 

Umm, Jason, perhaps a deep breath Is needed. I'm saying that If their was a problem that existed, I would have had 100's of PM's to suggest that the FD Alternator should not be an upgrade to a FC.

Besides, did you not read and comprehend that he has not made a DMM check?! *Geez*

 

Actually, you gave us a little clue earlier...
All I'm saying is that you should check it properly to see if you have a problem, but you seem to have a real issue with me offering you advice and info that might actually help you. It's not like I'm getting anything out of this y'know...

 

I'm not suggesting FD alternators are a problem. Whether it's FC or FD doesn't matter; neither are supposed to exceed 14.7V.
Dude, that's my whole point! He needs to check it properly! If the stock gauge (which "sucks" and is "inaccurate") suggests the voltage is too high, then you get a reliable meter and check it. You don't just ignore it for months. If the stock temp gauge starts to rise, do you just say "it sucks" and carry on? I hope not...

 

What the basis of this thread was to Implement an Underdrive Pulley and than eventually spilled over to the potential exceeding of 14.7v with his Alternator. As dDuB said way back was he was relying on the stock Voltage Guage. Right? Atleast give the scenario that. So why would you be persistant to dwell on readings that are being read off the stock Guage which were not only extracted from the stock Guage but were mentioned very early In the thread?

In a way, I'm Interested to know If the Voltage Regulator was fried as a byproduct of miswiring It Incorrectly at one point. In any case, both dDuB and I will deal with this accordingly. I'm a pretty fair guy. Anyway, nothing can be said further until a reading via a DMM Is done.