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Thread: 7" CRANK PULLEY WITH 2.5" SUPERCHARGER PULLEY

  1. #1
    Junior SCH Member
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    7" CRANK PULLEY WITH 2.5" SUPERCHARGER PULLEY

    my current setup is on my 82 bronco with a 5.0 engine.has a 270 comps cam with a bd-11a charger and a 76mm mass air system(no bypass valve).
    my truck only revs to 4000-4500rpm between shifts even at wot i never goto 5000 rpm. the bust i get at wot is 6 psi. the question that i have is if i go with the 2.5 pulley would this work with my truck application. because i would need the boost to kick in early and not later in the rpms.

  2. #2
    Senior SCH Member vinces427bb's Avatar
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    what size is your current pulley?
    2.75, 2.93, or larger than 3"???
    belt wrap is an issue with smaller than 2.93"-pulleys...

    i see you have a 270comp-cam = does that cam have a 110-LSA
    this will bleed off boost pressure,
    also your psi-boost is about at the level that a bypass would be needed.
    Last edited by vinces427bb; 02-19-2012 at 01:58 AM. Reason: additional info

  3. #3
    Junior SCH Member
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    my current pulley is stock 3inch pulley.the cam has a 112 lobe separation.

  4. #4
    Junior SCH Member
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    the problem is i'm having my boost come in late when about to shift. i'm trying to have it come in earlier at 1500rpm until 4500

  5. #5
    Senior SCH Member vinces427bb's Avatar
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    which comp cams 270 are you running with a 112-LSA??
    does the belt you have slip now?
    do you have a fresh belt or is it worn, NAPA has cheap/free belt gauge to check micro-V wear.
    if your belt is slipping you may see it on the boost gauge, boost rises to say 7-8psi then
    falls back to say 5-6psi while engine rpm is still climbing?
    a smaller pulley will give more boost earlier but will be more prone to slip earlier,
    because more boost pressure takes more torque/HP to turn the blower.

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