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Pulley change 3.75 to 3.5

Discussion in 'The Blower Bistro' started by Stage 4.6, Dec 20, 2019.

  1. Stage 4.6

    Stage 4.6 Well-Known Member Established Member

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    How drastic of a change in boost can i expect from swapping my current 3.75 to 3.5 pulley on my Kenne Bell 2.6H? Comparing them side by side there isn't much difference in size.
     
  2. 01yellercobra

    01yellercobra AKA slo984now Established Member

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    Not apples to apples, but on my D1 .1" was good for about 1psi. Either increase or decrease depending on which way you were going.
     
  3. MG0h3

    MG0h3 Well-Known Member Premium Member Established Member

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    @2 on G2 2.9 non crusher


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  4. Stage 4.6

    Stage 4.6 Well-Known Member Established Member

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    I was wondering if i should go with smaller pully, upon completing the switch to E85?
     
  5. 01yellercobra

    01yellercobra AKA slo984now Established Member

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    Might as well. Take advantage of the E85.
     
  6. 04DeadShort

    04DeadShort SVT Addict Established Member

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    In my experience each pulley size step is about 2psi. I would drop it down to 3.5, make sure the fuel setup is enough to supply the E85 and let her eat.
     
  7. Stage 4.6

    Stage 4.6 Well-Known Member Established Member

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    yeah Ill put the 3.5 on, I purchased the Fore Level 4 kit, so it will definitely have the supporting fuel system. I just don't want to keep going back for tunes, so debating if i should just purchase a 3.25 pully and get her done?
     
  8. 04DeadShort

    04DeadShort SVT Addict Established Member

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    Have a talk with your tuner and see what he recommends.
     
  9. Stage 4.6

    Stage 4.6 Well-Known Member Established Member

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    I will! appreciate all the advice.
     
  10. Stage 4.6

    Stage 4.6 Well-Known Member Established Member

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    *Update!
    I went with a 3.25in pulley and put it on the E. To my surprise on a conservative tune It only went up 2psi (16-18psi) from my previous set up?
     
  11. MG0h3

    MG0h3 Well-Known Member Premium Member Established Member

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    Well the tune is irrelevant as far as air volume/boost goes.

    I’ve experienced a decreasing amount of boost increase with blower RPM increase


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  12. Stage 4.6

    Stage 4.6 Well-Known Member Established Member

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    Makes sense! i just figured that pushing the motor harder on E, I would've seen an increase in boost. Regardless i am very happy with the results.
     
  13. c6zhombre

    c6zhombre E85 NutSwinger Established Member

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    The increase sounds a little short for a 3.75 to 3.25 swap.....but regardless....I think you need to spin that blower even more on E85. I think that KB 2.6 is capable of 24psi (sea level) with a 2.75 upper.....so maybe that's 22psi at elevation. The 3.0 upper says 22psi sea level.....I think at a minimum I'd go with the 3.0 on ethanol.
     
  14. Stage 4.6

    Stage 4.6 Well-Known Member Established Member

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    You are a correct sir! Blower is capable of at least 22psi up here. My tuner said pretty much exactly what you did. It is also on just 20 degrees of timing. I was planning on a 3.0in pully but i thought with the 4lb. lower combo Id be at 20psi?

    I was also considering switching blowers and getting a Whipple 2.9 Gen 3 crusher or Gen 4 standard inlet? but I wanted to see what the old KB 2.6H would do up here (722hp/693tq) with my current combo. Obviously it still has more to give.
     
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  15. c6zhombre

    c6zhombre E85 NutSwinger Established Member

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    Damn....722 is no joke! What is your ultimate power goal? I think you're at a great place right now.....but if you want to really push it towards 800 you'll need to swap for either the gen3 or 4 2.9. Just remember for every HP you start pushing past say 750...an entire new set of weak links will come up. You'll need ARP head studs for starters! Possibly a T56 magnum too.
     
  16. Stage 4.6

    Stage 4.6 Well-Known Member Established Member

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    My goal was to have a reliable 750hp Cobra, I never gave my tuner a number just told him get what he can out of it, driveability being the priority. I am aware and realize that if i push it any further i will be needing head studs. I am new to the E85 game so i think i will enjoy as it sits for awhile.
    The tranny in this car has been a thorn in a$%, never shifts smooth so that will mostly be my next mod.
     

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