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Old 09-22-2008, 10:54 PM   #1
NORAB
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Default Alternator messin' with performance?

I just ordered a new alternator due to the fact that it was just that time for it to go...but i was wondering could an alternator impact performance (power) of a WRX or any vehicle? if so to what extremes?

i was noticing hesitation when the motor starts as if it wants to die for a WHILE now...my car battery died today so i finally got it checked and it was a bad alternator. along with the hesitation my lights dimming and whining noise at start up.

any takers?
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Old 09-23-2008, 02:16 AM   #2
Clark Turner
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Yes. Your alternator produces higher voltage which drives your Coil packs to higher voltage. Your fuel injectors are also driven off of voltage pulses. There is a voltage offset map to compestate for the fuel injectors but it is seldom acurate.

These cars tend to have low voltage. Your 02 is def low voltage. Mine has 12.6 at idle and no more then 13.5 going down the road. This is just enough to charge the battery.

I had a WRX on the dyno once and did a test. I hooked a full size floor standing Battery charger/starter to the car and did a dyno pull. I made an additional 20whp almost across the board. I unhooked it and the power dropped down. Nobody seemed to believe me. I was searching for a way to add 1 to 1.5 volts. This is common to in the GM world. Companys make plug in voltage devices that raise the voltage for this very reason. GM owners report more power ect...

One thing you can do, Is buy a V7 or V8 JDM alternator. They are higher map rating because the JDM cars had DCCD difs and HID headlamps. They bolt right on and are a direct replacement.



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Old 09-23-2008, 06:30 AM   #3
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What are the alternatives if we can't find a JDM alternator.Do you know if the USDM sti (06-07) fits also?
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Old 09-23-2008, 10:09 AM   #4
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subscribed. I am interested in this!
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Old 09-23-2008, 10:14 AM   #5
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I was wondering if it was possible to put a resister on the sensor wire to fake the alternator into putting out higher voltage. There's a 10 amp fused line from the battery line to the alternator which looks like how it senses what the current voltage is. I imagine reducing the voltage in that line by 1 volt would make the alternator increase voltage by 1 volt. You'd have to measure the current through that line to pick a resister.

Is the STI one even better?

Manual says they should be putting out 14.1-14.8 volts and that the STI one's the same as any turbo car.
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Old 09-23-2008, 10:34 AM   #6
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Quote:
Originally Posted by Clark Turner View Post

These cars tend to have low voltage. Your 02 is def low voltage. Mine has 12.6 at idle and no more then 13.5 going down the road. This is just enough to charge the battery.
My 02 sees 14.2-14.4v at start up and generally 13.6-14v crusing/idle.Stock alt.
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Old 09-23-2008, 10:47 AM   #7
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^^
me too on my 04.

Or so says my X50
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Old 09-23-2008, 10:53 AM   #8
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Quote:
Originally Posted by boqueron00 View Post
What are the alternatives if we can't find a JDM alternator. Do you know if the USDM sti (06-07) fits also?
I got this one
http://www.maniacelectricmotors.com/11058hiamp.html
but I didn't really get any improvement at all. Under full load (AC on full blast and lights on), I'm still seeing voltages as low as 12.28. But then again, my idle doesn't go past 750rpm for some reason under full load.
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Old 09-23-2008, 11:28 AM   #9
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along with me ordering a reman alternator i got a ground kit too...from Paranoid Fabrications. i heard nothing but good things from them; the kit should get here probably by friday along with the alternator...ill let ya know how the car runs with them on.
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Old 09-23-2008, 12:30 PM   #10
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I made my own grounding kit and it made a very very little difference but I seen the difference on my volt gauge.
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Old 09-23-2008, 12:45 PM   #11
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i made a grounding kit over the weekend..the DIY by davenow in the electrical/lighting forum..not sure if it was there before but my alternator is making a buzzing sound..i listened to my friends 03 and his didnt make that sound..the only thing different i did from davenows setup was that the last ground i put on the passenger strut top for now since i couldnt get a bolt to go into a hole in the passenger side head..im thinking either moving it to the fender wall or the intake bolt

my setup is on the last page

http://forums.nasioc.com/forums/showthread.php?t=674153
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Old 09-23-2008, 02:12 PM   #12
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Keep in mind that if you get a higher amp alternator, You will have less voltage and current at idle over the stock alternator. The only way to offset this is to use a smaller pulley on the alternator. That 140 amp alternator is going to work better then the stock alternator but not until 2000+ rpm.

I have researched how to trick the alternator into producing higher voltage, but just ran out of time. I am sure there is a way to make a plug in resistor or diode arrangment that will increase the voltage. GM alternators work this way and you can buy a plug in voltage booster that will add 1, 1.5 and 2 volts. I would want 14.5 volts personaly.

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Old 09-23-2008, 02:36 PM   #13
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If you know the current draw on the sample wire, doing a voltage drop resister is simple math. You'll need to size the resister to the current level though. 1 volt drop at 10 amp = 10 watts which is a big assed resister. It it's only 1 amp then it's 1 watt. If it's variable then a resister isn't the right tool. You'll need a voltage regulator.
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Old 09-23-2008, 03:58 PM   #14
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Quote:
Originally Posted by Clark Turner View Post
Keep in mind that if you get a higher amp alternator, You will have less voltage and current at idle over the stock alternator. The only way to offset this is to use a smaller pulley on the alternator. That 140 amp alternator is going to work better then the stock alternator but not until 2000+ rpm.

I have researched how to trick the alternator into producing higher voltage, but just ran out of time. I am sure there is a way to make a plug in resistor or diode arrangment that will increase the voltage. GM alternators work this way and you can buy a plug in voltage booster that will add 1, 1.5 and 2 volts. I would want 14.5 volts personaly.

Clark
I had thought about a smaller pulley, but I was afraid I'd have to find a corresponding belt through trial and error.

I remember seeing a thread a while back about those voltage boosters but I couldn't find what the guy was talking about using the link he provided.
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Old 09-23-2008, 07:39 PM   #15
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The belt size is the width by the length.. Just go to the auto parts store and get the next size shorter.

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Old 09-23-2008, 08:50 PM   #16
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If the regulator in the alt's doing it's job, spinning the alt faster isn't going to make more voltage. It might help at idle but, not while cruising.
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Old 09-23-2008, 09:37 PM   #17
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bad grounds are the vast majority of cases of low voltage, at least next to a completely failing voltage regulator. go through and fix grounds first, and then keep looking for problems if the voltage is still low.
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Old 09-25-2008, 09:10 PM   #18
NORAB
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yeah, car runs a heck of a lot harder with a fresh alternator on...

plus i got that ground kit on...meh, its ok...i thought the car would feel like a different car. it does, but only at idle (it idles strangely quiet). plus i notice a slight harder pull in 3rd gear.

to be honest im just glad i got my wrx fixed not even if i couldnt get it to run faster...i hate having a half dead battery at start up.
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Old 09-26-2008, 12:02 AM   #19
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I too am experiencing low voltage. In fact we believe it is causing a slight misfire in the high rpm range when the boost is turned up. Did a modified version of DaveNow's grounding mod and replaced my alternator with a reman one. I am still having the same issues. Going to hunt for ground issues this weekend.

Anyone want to be a guinea pig ??
They even have stage 1 and stage 2!
At that price I might even donate one if somebody wanted to try it!

Can anyone verify Clark (no offense man) on the JDM alternators being higher Amp units? One of the guys over at JDMSpecC didnt seem to think so when I called today.
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Old 09-26-2008, 12:16 AM   #20
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The jdm and Sti alternators are 90 amps and wrx are 75, I had a V7 jdm alt and it died so I have a 2007 Sti alternator now
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Old 09-26-2008, 12:24 AM   #21
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Quote:
Originally Posted by jmlaser View Post
I too am experiencing low voltage. In fact we believe it is causing a slight misfire in the high rpm range when the boost is turned up. Did a modified version of DaveNow's grounding mod and replaced my alternator with a reman one. I am still having the same issues. Going to hunt for ground issues this weekend.

Anyone want to be a guinea pig ??
They even have stage 1 and stage 2!
At that price I might even donate one if somebody wanted to try it!

Can anyone verify Clark (no offense man) on the JDM alternators being higher Amp units? One of the guys over at JDMSpecC didnt seem to think so when I called today.
Shoot, I'd be willing to try it but how de we know that would even plug into our existing regulator.
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Old 09-26-2008, 10:12 AM   #22
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There's only 3 wires into and out of the alternator. There's not much that could be wrong.

When you guys are measuring voltage where are you measuring from? I'd see what's the voltage is AT the stud that sticks out of the alternator to the case of the alternator. If that's 14.5 volts but, your battery voltage is 12-12.5 then the problem is either ground or voltage drop between the alternator cable and the battery/fuse box (I don't have the circuit in front of me). I have to imagine a weak cell on the battery could pull the voltage down too. If your battery's 5 years old, it's on borrowed time.
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Old 09-26-2008, 09:21 PM   #23
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My Interstate is 1 year old,alternator is reman and is 2 weeks old...
AS far as voltage goes I see about 13.65 @ alternator, 13.4 measuring directly at the back of the ECU on the power supply pins. This is about the best voltage I have gotten and it often drops as the car warms up. I usually watch it on the AP and it goes from 13.4 to as low as 12.9V. (although I am not sure where the AP reads this voltage, will have to ask Cobb about that)

Also I thought it was odd that I had 3 to 4 ohms from the ECU pin grounds to the body ground. Does this sound excessive to anyone else?

Quote:
Shoot, I'd be willing to try it but how de we know that would even plug into our existing regulator.
I am sure we would have to look at the pin-out on our cars and the car they are designed for and do some modification.
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Old 09-26-2008, 09:28 PM   #24
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3-4 ohms is alot. 1/2 AMP draw means a voltage drop of 2 volts across the ground. I'd think it should be well under 1 ohm, effectively zero.
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Old 09-26-2008, 11:20 PM   #25
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This thread has me thinking. Most of us know the importance of proper voltage at the coil packs, and how it can affect performance. I just don't know why it hasn't REALLY been discussed before. After this thread came up, I did some searching and came up with a few things. Though they may/not be worthy, or even work at all, i'm sure it can get the ball rolling on anyone trying to help us out.


First found this. Sun Auto Voltage Stabilizer
http://www.racinglab.com/hyper-voltage-gt-subaru.html


It has its own review in the parts review section, but its not very conclusive, and doesn't say anything about logging voltage.

but then stumbled upon this http://www.speedelement.com/index.ph...mart&Itemid=38
and review
http://forums.nasioc.com/forums/show...hlight=voltage

anyone have any thoughts? This could be big.
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