Difference between the upper and lower pulley?

Discussion in 'SRT Hellcat Builds' started by Hemibuck, Jan 28, 2016.

  1. Hemibuck

    Hemibuck Gold Member

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    So this is my first blown car and I'm a little ignorant when it comes to the pulleys and how they change the power output. Can someone break down the difference between changing the upper and lower pulley. Also the location of the lower. I think I understand where the upper is located and it seems to be working great for most with a tune. I will be waiting to see the longevity of these recent upgrades before I decide to pull the trigger. hanks in advance for the advice!
     
  2. Lord Hellcat

    Lord Hellcat Gold Member Hellcat Car Club Gold Supporting Member HCC UK President HCC Charter Member

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    The lower pulley is the crankshaft pulley
     
  3. Hemibuck

    Hemibuck Gold Member

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    Got it. I'm not messing with that one. I might do the upper and a tune someday. Thanks.
     
  4. Lord Hellcat

    Lord Hellcat Gold Member Hellcat Car Club Gold Supporting Member HCC UK President HCC Charter Member

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    I am doing the upper pulley 2.85 and installing the ATI superdamper standard size. Tuning by HHP. Looking forward to getting it all done by the end of next month
     
  5. Hemibuck

    Hemibuck Gold Member

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    Can you exsplain the difference in the size of the upper? I have heard that one is more for a street set up and the other is for a race set up. Also is the ATI a new crank pulley?
     
  6. Hemibuck

    Hemibuck Gold Member

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    The crank (lower pulley) is going to turn the motor over faster and the upper is turning the SC faster correct?
     
  7. Ray Hunsaker

    Ray Hunsaker Silver Member Hellcat Car Club Gold Supporting Member HCC Charter Member

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    is what they do is spin the blower faster upper is smaller lower is bigger. its easy the change the upper (once you have the metco) back to stock or race pulley or in my case ive have a 285 to make up for altitude.
     
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  8. BeeHappy

    BeeHappy Hellcat Member

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    Crank "drives" everything

    ratio changes

    stock gives you 11-12 psi

    1. smaller blower pulley with stock crank pulley gives you more psi...say 13psi

    2. larger crank pulley with stock blower pulley gives you ......say 15psi

    3. larger crank pulley with smaller blower pulley gives you ....say 17-18 psi

    *now psi is not real but you can see how it progresses.

    1. change the upper pulley get mild boost

    2. change lower pulley get med boost

    3. change both....get lots of boost
     
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  9. Hemibuck

    Hemibuck Gold Member

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    Got it thanks!
     
  10. Hemibuck

    Hemibuck Gold Member

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    Ok got it. Looks like they are getting great gains with just the upper and a tune with stock intake and exhaust. That is amazing considering you don't need to drop coin for intakes and exhaust and can get almost 100 HP.
     
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  11. TrackDay

    TrackDay Silver Member

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    It's all about the ratio of the damper diameter to the supercharger rotor pulley. Make the upper pulley smaller and the supercharger rotor spins faster for the same engine speed. Make the damper larger and the pulley ratio also increases so the supercharger rotor spins faster for the same engine speed.

    The ATI pulley alone results in about a 2.6 pulley ratio vs a 2.4 stock. If you leave the damper stock and run the 2.85 in upper pulley it is an even higher ratio, by memory closer to a 2.8. Change both pulleys and you get even higher pulley ratio.

    The Metco range is wide enough I don't see the need to change the damper anymore.
     
  12. Mr. Robert Lee Jones

    Mr. Robert Lee Jones Silver Member

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    I had a really bad experience with the last car I started fing around with. So I'm terrified of screwing up my HC. But would love to do the upper pulley and tune.
    What is the downside? Why would I not do this? Has anyone had a bad experience with upper pulley and tune?
     
  13. Hemibuck

    Hemibuck Gold Member

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    I feel the same way. Why not? I am sure we run the risk of blowing gaskets with the extra boost but it's not a ton more. I feel that these cars were making close to 800 in the pre productions versions and they took it down to make it compliant with EPA standards. So I am sure we will have little to no problems with the upper and a tune but I am going to wait for a few more months before I decide to do it. Withing a year we will see what the weak points of the upper and a tune are. It's hard to not wan another 100 HP though....hehe!
     
  14. Draggin

    Draggin Rookie

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    If you want to start screwing with the pulleys put long tube headers with no cats. These cars build a lot of heat and I know of a couple cars that have lifted ringlands. Also if screwing with either pully you will want to pin the crank.
     
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  15. Hemibuck

    Hemibuck Gold Member

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    At the cost and PIA factor of installing long tubed and cat delete no thanks.
     
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