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Thread: Pulley Selection V2 SI

  1. #1
    Junior SCH Member
    Join Date
    Dec 2012
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    6

    Pulley Selection V2 SI

    hi all.....
    just about done changing out the Powerdyne bd11a on my 360 Chrysler for a V2 SI that i have just purchased. The powerdyne was not going to give me the boost i want.
    Anyways what i would like to know is what head unit pulley to use for say 12psi boost @ say 6000rpm, 7" crank pulley, 3.5 rear, auto. i have a couple of spare pulleys from the powerdyne, but they are 2.7 and 2.9. think they may be too small.

    cheersP1010441.JPG

  2. #2
    Senior SCH Member vinces427bb's Avatar
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    Jul 2011
    Location
    Los Lunas, NM
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    222
    welcome to the site.
    looks like it packaged under the hood well.
    what kind of boost are you getting now before changing pulleys??

  3. #3
    Junior SCH Member
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    Dec 2012
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    6
    about 6, but that was with 6" crank pulley and 2.7 on the head unit.

  4. #4
    Senior SCH Member vinces427bb's Avatar
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    Jul 2011
    Location
    Los Lunas, NM
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    222
    Powerdyne bd11a has max impeller speed of 38,000rpm with an internal step-up ratio of 3:1;
    therefore 6psi-boost with 6" crank pulley and 2.7 on the head unit = only 21960 blower speed @ 6000rpm-engine speed =122% overdriven
    with 7" crank pulley and 2.9 on the head unit = only 25380 blower speed @ 6000rpm-engine speed =141% overdriven
    with 7" crank pulley and 2.7 on the head unit = only 28620 blower speed @ 6000rpm-engine speed =159% overdriven

    wallace has many calculators on this site.
    http://www.wallaceracing.com/blower-od-calc.php
    this one can tell you the %-of UD/OD ratios of the crank/blower pulley, then times by the rpm and times by the 3:1 step-up ratio to end up with the blower speed at engine rpm

    you can spin the blower much higher than you are now with the 7''crank and either 2.7/2.9''blower pulleys
    providing the max-blower rpm and set-up ratio i used are correct

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