Pulley change???

Discussion in 'PSI Superchargers Tech Questions' started by blownfever, Jul 1, 2012.

  1. blownfever

    blownfever Member

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    If I change 14-71 blower pulley on 540ci BBC from 47%od to 63%od should the bv jet be changed also???? Currently it is at 47%od and bv jet 140, so should it be changed to a 145 with 63%od?? Thanks
     
    #1
    blownfever, Jul 1, 2012
  2. Critical Mass

    Critical Mass Member

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    Blownfever,
    That's a lot of overdrive. You might not see the change you are looking for due to blower heating of the air with a roots. I would take a good look at your plugs and use the jetsize software to arrive at the proper main jet size. I would start with smaller steps before going to that big of a jump.
    Be careful, Joe
     
    #2
    Critical Mass, Jul 1, 2012
  3. ta455

    ta455 Member

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    from 140 to a smaller number should be better i think.
     
    #3
    ta455, Jul 1, 2012
  4. Relentless

    Relentless www.bretitanium.com

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    You will go slower if this is standard helix blower as you will just create heat not power.

    For hi helix, that's quite a jump, but go SMALLER main not larger or you will hurt it...
     
    #4
    Relentless, Jul 2, 2012
  5. bandit496

    bandit496 Member

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    Kinda depends on where your setup is now--what do the plugs look like? We are limited to 45% on 14-71 straights (540 BBC)and our pill is nowhere close to 145, more like the 110-120 range. But to go to that OD, you will heat the air (which ain't good) and your pill size should go smaller if you increase the OD. JW
     
    #5
    bandit496, Jul 2, 2012
  6. blownfever

    blownfever Member

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    At 47%od the plugs were black with a 140, although my timing was 29 (30lbs boost).....
    Moved the timing to 32 and pulley to 63%od and will put 135 in to try it... Spud helped with previous fuel setup for a starting point but he is not available right now!!! I know 63od is a lot but it helps running under 200ft wot in sand/mud drags.... In 2 seconds it don't get much time to build heat. Thanks ITA
     
    #6
    blownfever, Jul 2, 2012
  7. Mike Canter

    Mike Canter Top Dragster
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    Just to make sure you understand that black plugs are not fouled because it is running way rich. Like new on the cadmium is rich, black is leaner on the way to a lean frosty.
     
    #7
    Mike Canter, Jul 2, 2012
  8. nitrowannabe

    nitrowannabe Member

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    Could someone tell me how going from 47% od to 63% od only increases the blower speed 10.88% ?
     
    #8
    nitrowannabe, Jul 2, 2012
  9. Wildcatracing

    Wildcatracing Member

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    1.63 divided by 1.47 = 1.1088% or 10.88% more air
     
    #9
    Wildcatracing, Jul 2, 2012
  10. blownfever

    blownfever Member

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    Mike, do you think I need to go even lower like a 125-130 and try it? I was thinking it was still way rich with black plugs!!! I don't want to lean it too much and detonate. Right now I'm just trying to get it close and read plugs
     
    #10
    blownfever, Jul 2, 2012
  11. MotorPsycho

    MotorPsycho Member

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    Read Mike's guide on reading plugs, priceless information :cool:
     
    #11
    MotorPsycho, Jul 3, 2012
  12. Mike Canter

    Mike Canter Top Dragster
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    You are way safe where you are. You stay on the throttle for such a long time. You will see some performance gain by going leaner but not much. You asked if you should go smaller to lean and that is incorrect. To go leaner you should go larger on the main jet and bypass more fuel. If it was me I would go leaner five jet sizes at a time until I started to see some frost on the plugs but that would be after one run on NEW plugs. You can put in just two new plugs at a time. I bet you are leaving your plugs in for many runs right now and that is why they look black.
     
    #12
    Mike Canter, Jul 3, 2012
  13. Don Onimus

    Don Onimus New Member

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    plugs

    Are you starting it with gas? That will make the plugs look black. Listen to Mike. He KNOWS. Don
     
    #13
    Don Onimus, Jul 4, 2012

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