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BMW 3-Series (E90 E92) Forum > E90 / E92 / E93 3-series Powertrain and Drivetrain Discussions > NA Engine (non-turbo) / Drivetrain / Exhaust Modifications > Underdrive Pulleys?



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      11-25-2012, 12:45 AM   #1
SDemetris
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Underdrive Pulleys?

I saw that underdrive pulleys are available for the M3 and i know thats a pretty common mod for other cars that Ive had before, but ive never seen anyone talking about it for our car. Im not really sure how our whole accessory system is set up, so it might not be possible but can anyone tell me more about this for the n52?
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      11-25-2012, 05:05 PM   #2
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^ interested
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      11-25-2012, 05:12 PM   #3
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They have never caught on with the N52. If i remember correctly someone bought a kit and either lost power or had problems.
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      11-25-2012, 05:14 PM   #4
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Not worth doing, we have an electric water pump and the alternator runs to many things to be under drivin without issues, the AC compressor also disengages under WOT.
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      11-25-2012, 06:04 PM   #5
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ok. that makes sense to me
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      11-27-2012, 11:47 PM   #6
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So can we get a better water pump???
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      11-28-2012, 08:47 AM   #7
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Isn't the oil pump also electrically driven?

I'd stay away from under driving the alternator. Any gain in power would likely be minimal at best. Even on older 4th Gen Camaro's with LT1 V8's the underdrive pulley would only net about 2 hp.
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      11-28-2012, 03:52 PM   #8
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the only think you would save is the rotating mass from a lighter pulley but you would never notice it.
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      11-28-2012, 05:12 PM   #9
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not worth is... a custom pulley kit (which you would have hire an automotive engineer to design one) would cost around $2,000k+... with only gains of around +3-5hp (5hp if you underdrive the alternator - not for audiophiles). Cost vs performance is not worth it... not to mention, the average garage joe can't install them himself without the proper tools and measurement devices for proper tension.

Installation usually involves removing the radiator fan (extreme cases demands taking out the entire radiator) loosening the belt tensioner, then removing the appropriate pulley(s), then returning to tension specs as per BMW... it IS possible to DIY, but it takes trial and error to listen and feel for faults in the tension until you get it right and risk damaging your engine/crankshaft/components.

So with that said... Cost vs Effort vs Performance is waaaaay not worth it...

and this is where you would start: http://www.intent-design.com/innovative-services.php

also, i'm not sure where "the" guy bought one, but i wouldn't be surprised to think that it wasn't meant for N52. There was a rumor that the E36 3.0L pulley kit would work, but i talked to TurnerMotorSports about it and their engineer was certain that the pulley system is thoroughly different as there is no pulley-driven water pump. If you can find the article, can you reply with the link?
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Last edited by N0OS3; 11-28-2012 at 05:29 PM.
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