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E36 (1991 - 1999)
The E36 chassis 3-Series BMW was a huge hit among driving enthusiasts from the first moment the car hit the pavement. The E36 won numerous awards over the years it was produced and is still a favorite of many BMW enthusiasts to this day! -- View the E36 Wiki

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  #1  
Old 10-29-2008, 08:48 AM
john1in2 john1in2 is offline
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"undo" increased HP w/ underpower pulley?

As I'm thinking of ways to up my HP I thought of this question- if you increase your HP with a chip, CAI, exhaust, etc.... is there a risk that you will overpower your alternator? If so, is it pretty standard to put in an underpower pulley to drop the alternator by 10-15% in order to "undo" the HP increase to alternator as well as to increase the overall HP even more?
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E36 Stats: 1995 325is: 125Kmi; TSW Rims; Bilstein shocks; K&N panel filter; Pioneer/ Polk audio CD/MP3; Conforti Chip; NGK Iridium plugs. Original owner.
E36 Replacements: drivers seat leather (1), wheel bearings (3), water pump (1), radiator (1), rear brake light assembly (1), battery (3).
E46 Stats: 2004 M3, 45Kmi (3rd Owner)

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  #2  
Old 10-29-2008, 12:29 PM
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98_328i 98_328i is offline
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The horsepower rating of the engine has nothing to do with the output of the alternator. The alternator is powered by the rotation of the pulley on the alternator itself. Underdrive and overdrive pulleys change the rotation speed of the pulley and that's it. Think of the large and small sprockets on a bicycle chain and you'll get the idea.
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  #3  
Old 10-29-2008, 08:21 PM
john1in2 john1in2 is offline
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Forget about the alternator output. I am thinking about the INPUT. If you increase HP are you not increasing the speed at which the alternator input belt turns and thus causing the alternator to deliver more voltage and current that it normally would?
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E36 Stats: 1995 325is: 125Kmi; TSW Rims; Bilstein shocks; K&N panel filter; Pioneer/ Polk audio CD/MP3; Conforti Chip; NGK Iridium plugs. Original owner.
E36 Replacements: drivers seat leather (1), wheel bearings (3), water pump (1), radiator (1), rear brake light assembly (1), battery (3).
E46 Stats: 2004 M3, 45Kmi (3rd Owner)

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  #4  
Old 10-29-2008, 10:24 PM
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Quote:
Originally Posted by john1in2 View Post
Forget about the alternator output. I am thinking about the INPUT. If you increase HP are you not increasing the speed at which the alternator input belt turns and thus causing the alternator to deliver more voltage and current that it normally would?
?????

No. Why would you think that? Your engine turns at the speed indicated by your tachometer, no matter how many HP you have. Remember your redline? It will never go faster than that on it's own power. Anything in that band is perfectly safe for your alternator.
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  #5  
Old 10-29-2008, 10:30 PM
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Originally Posted by E36 Phantom View Post
?????

No. Why would you think that? Your engine turns at the speed indicated by your tachometer, no matter how many HP you have. Remember your redline? It will never go faster than that on it's own power. Anything in that band is perfectly safe for your alternator.
Yes. What he said.
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  #6  
Old 10-30-2008, 01:08 PM
john1in2 john1in2 is offline
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Quote:
Originally Posted by E36 Phantom View Post
?????

No. Why would you think that? Your engine turns at the speed indicated by your tachometer, no matter how many HP you have. Remember your redline? It will never go faster than that on it's own power. Anything in that band is perfectly safe for your alternator.
Cause I'm an idiot!

- thanks for the information, I get it now.
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E36 Stats: 1995 325is: 125Kmi; TSW Rims; Bilstein shocks; K&N panel filter; Pioneer/ Polk audio CD/MP3; Conforti Chip; NGK Iridium plugs. Original owner.
E36 Replacements: drivers seat leather (1), wheel bearings (3), water pump (1), radiator (1), rear brake light assembly (1), battery (3).
E46 Stats: 2004 M3, 45Kmi (3rd Owner)

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  #7  
Old 10-29-2008, 10:31 PM
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Quote:
Originally Posted by john1in2 View Post
Forget about the alternator output. I am thinking about the INPUT. If you increase HP are you not increasing the speed at which the alternator input belt turns and thus causing the alternator to deliver more voltage and current that it normally would?
That's what the voltage regulator is for. It ensures that the alternator delivers the same amount of voltage from idle to redline. Also, the alternator is not always producing current. It cycles on and off based on electrical demand. If it was producing current 100% of the time it would burn up.
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Old 10-30-2008, 03:42 PM
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No big. Actually, glad you asked in case anyone else thinks that at some point, too.

Nice looking M3 man!
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