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11272012, 11:22 PM  #89 
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Rogue said explicitly that with both of their systems, 1 and 2 pulleys, that all systems are underdriven by the same 16% figure. The point of the 2nd pulley in the 2 pulley system (included in a note in the spreadsheet) is to be able to use readily accessible belts (as pointed out also in a post just above).
Last edited by swamp2; 11282012 at 01:55 AM. 
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11282012, 05:14 PM  #90 
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The AFE is 4.124" in diameter, according to my calculations this makes it a 84.5 of the OEM diameter or a 15.5% reduction if my calculations are correct.
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2013 M3 CoupeMR/BLK ZCP, ACM test pipes, BPM Stg2 dev. tune and Megan catback, AFE Stg2. with C/F elbow
Previous rides: 2011 M3 CoupeMR/Blk 2007 Porsche 997C2S Speed Yellow/Blk sport seats 2004 BMW M3 Imola/Blk 
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11282012, 09:16 PM  #91 
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Great, thanks. Does this also mean you measured the OEM pulley at 124mm (4.88"). In the calculations for the AA pulley I used 122mm as the OEM size. I will use these figures for an update.

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11282012, 09:19 PM  #92 
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11282012, 09:59 PM  #93  
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Swamp I didn't know the exact size of the OEM pulley just what I saw someone else post up. I used 124mm for OEM, if its 122mm then I am off a bit. Dave
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Previous rides: 2011 M3 CoupeMR/Blk 2007 Porsche 997C2S Speed Yellow/Blk sport seats 2004 BMW M3 Imola/Blk 

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11282012, 10:27 PM  #94 
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Thanks for clarifying. This means the AA and AFE numbers in the table are still potentially off a percent or two. Anyone with a precise number here?

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11292012, 12:24 AM  #95 
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Looking at your sheet swamp, there's a small error on a technicality. The AA pulley is shown as coming with 2 belts when it actually comes with 3. 2 for use with the new crank, and 1 extra belt for the double sided application. I'll try to get an exact measurement tomorrow on my removed stock pulley. I'll post a picture like Andrew did if I can find the time in the evening, using the same style digital caliper.

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11292012, 02:01 AM  #96  
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Thanks in advance for any measurements you can share. IMHO there is absolutely no need to post a fancy picture like that "proving" a number. If you're a contributing member here and you know how to zero and use a caliper, no one should question a simple distance measurement on a small part. Really  don't waste your time. 

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11302012, 01:05 AM  #98  
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Dave
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2013 M3 CoupeMR/BLK ZCP, ACM test pipes, BPM Stg2 dev. tune and Megan catback, AFE Stg2. with C/F elbow
Previous rides: 2011 M3 CoupeMR/Blk 2007 Porsche 997C2S Speed Yellow/Blk sport seats 2004 BMW M3 Imola/Blk 

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12022012, 12:26 PM  #99 
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Is there any proof that the underdrive on the water pump actually has an effect in high rpm running? Many OEM pumps are on the right side of their envelope once you get within 2000 rpm of redline, underdriving the pump can actually help ontrack cooling on some cars.
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12032012, 03:53 AM  #100 
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I understand cooling may be diminished and depending on the pulley setup you choose the A/C system as well.
But has anyone running these pulleys noticed any power steering lag during quick corrections? I would hate to install a set and then have the power steering not react 100% while quickly correcting unanticipated oversteer, etc. Also, I haven't seen the charging system addressed. All of these pulleys must underdrive the alternator as well? I know the M3 charge system is already very weak.. just spent $500 on a new battery. 
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12032012, 12:45 PM  #101  
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12032012, 03:09 PM  #102 
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Some speculation but I would expect if there was not enough rpm/power/pressure in the PS system that the response would be a heavier feel rather than a lack of response. Due to safety the power steering is almost always a boost on what can be done purely manually.

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12032012, 09:12 PM  #103  
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Yes you are correct that the AA kit requires 2 special belts, but it does comes with 3. In case you or anyone didn't know that, I thought I would mention it. 

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12312012, 07:55 AM  #108 
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I've read that the e9x M cars decouple the alternator under full throttle.
Assuming this is true, the % by which the alternator pulley is underdriven is irrelevant with respect to peak hp gains. 
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12312012, 05:24 PM  #109 
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exactly! I always have preached underdrive pulley's no longer are worth it. The A/C and alternator are already disengaged under large throttle which means the only thing that is underdriven is powersteering and engine cooling. The two things I would never want to have heat up more than normal.
In older cars it was more worth it because you had all 4 systems sucking power but in new bimmers, you only have the water pump and power steering sucking power. I hope with newer engines they go with electrical water pump like the N52 engine. That way it would completely eliminate the need for an underdrive pulley. Especially if they go electric steering which they will. Actually may eliminate the need for a accessory drive if they can change how the A/C is run. This would probably free up 1520 hp consistently in cars and save on mileage. That is a winwin and should be the focus for bmw on m cars rather than going turbo. Lighter cars and elimination of parastic losses and direct injection could have netted great mileage on naturally aspirated high revving cars to meet both mileage and enthusiast desires 
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01062013, 09:32 PM  #110  
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Unfortunately I did not have a pair of calipers large enough to fit around the pulleys. Can anyone from EAS chime in with the measurements? 

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