3.09 A8 gear swap

Discussion in 'SRT Hellcat Performance' started by paul suloff, Sep 2, 2015.

  1. paul suloff

    paul suloff Silver Member

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    Anyone gone to a deeper gear? I see there is a complete drop in center available from HHP. Seems like an easy upgrade if it will give you a couple tenths.
     
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  2. srtfan

    srtfan SRT Hellcat Supporter Gold Supporting Member

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    I like where this is going...
     
  3. Top Cat

    Top Cat Gold Member Hellcat Car Club Gold Supporting Member Fastest Cat/Record Holder HCC Charter Member

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    Done, only one outing so I can't give too much feed back.
    TC
     
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  4. paul suloff

    paul suloff Silver Member

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    Is the one HHP offers the same unit as stock hellcat? 9" with same internals? Assume ring gear is not welded to carrier.
     
  5. TallCool1

    TallCool1 Gold Member Hellcat Car Club Gold Supporting Member Nat'l Hellcat Tech Advisor HCC Charter Member

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    paul suloff I'm kinda wondering same this appears like it's off the shelf for the a8 392 cars.

    Top Cat do you know of any differences between this and the stock rear end? Thank you.
     
  6. paul suloff

    paul suloff Silver Member

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    Not getting much feedback from HHP on improvements. There car is modified with power adders. I'd like to know with the 3.09 what trans gear a stock car will be in and at what RPM at the 1320? Many times a gear change can hurt performance by applying too much power down low or adding a gear change down track putting the engine out of the power band. Like to hear from the engineering types here to calculate RPM in each gear 2.62 vs 3.09 in 1/4 mile.
     
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  7. TallCool1

    TallCool1 Gold Member Hellcat Car Club Gold Supporting Member Nat'l Hellcat Tech Advisor HCC Charter Member

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    TIGwelder wanna run the math and numbers?
     
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  8. TIGwelder

    TIGwelder SSDD

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    With 2.62

    1st -- 4.714 x 2.62 = 12.351 ( x 336 = 4,149 ) = 41.5 MPH @ 6000 -- 42.8 MPH @ 6200
    2nd -- 3.143 x 2.62 = 8.235 ( x 336 = 2,766 ) = 62.3 MPH @ 6000 -- 64.3 MPH @ 6200
    3rd -- 2.106 x 2.62 = 5.518 ( x 336 = 1,854 ) = 92.9 MPH @ 6000 -- 95.9 MPH @ 6200
    4th -- 1.667 x 2.62 = 4.368 ( x 336 = 1,467 ) = 117.3 MPH @ 6000 -- 121.29 MPH @ 6200
    5th -- 1.285 x 2.62 = 3.367 ( x 336 = 1,131 ) = 152.2 MPH @ 6000 -- 157.32 MPH @ 6200
    6th -- 1.000 x 2.62 = 2.620 ( x 336 = 880 ) = 195.6 MPH @ 6000 -- 202.20 MPH @ 6200
    7th -- 0.839 x 2.62 = 2.198 ( x 336 = 738 ) = 233.3 MPH @ 6000 -- 241.11 MPH @ 6200 ( we're past the aero limit here )
    Then we enter driving in a vacuum land :)
    8th -- 0.667 x 2.62 = 1.748 ( x 336 = 587 ) = 293.3 MPH @ 6000 -- 303.13MPH @ 6200


    With 3.09

    image.jpg
     
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  9. TIGwelder

    TIGwelder SSDD

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    Without slipage, looks like still in top of 5th gear
     
  10. paul suloff

    paul suloff Silver Member

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    Great Thanks!!!:)
     
  11. TIGwelder

    TIGwelder SSDD

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    Compare to a 727's first gear, it would be like having 5.94 gears haha
     
  12. paul suloff

    paul suloff Silver Member

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    If it's at the top of 5th in lights that's good. If it blows the tires off down low, that will kill the benefits. Might have to go to bias slicks over 305 45 18 DRs
     
  13. Top Cat

    Top Cat Gold Member Hellcat Car Club Gold Supporting Member Fastest Cat/Record Holder HCC Charter Member

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    We only made three pass's with the rear change and no full pass as the car was not running right, but we did pick up big time on the 60' and I expect to see 1.38 or better when we start with all the HP available, I don't expect to change back to slicks, the DR are working great and should be fine with more power, IMO I think I could use a 3.25 gear and still have good traction.
    TC
     
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  14. DB2

    DB2 Silver Member

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    Im going through the traps in 5th gear at about 4700 rpm.

    Jeeeez.....you think this thing would pop wheelies with the right tires and any steeper gear!
     
  15. paul suloff

    paul suloff Silver Member

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    3.09 Should be at the top of 5th gear.
     

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