Shock Tuning Help

Discussion in 'Drag Racing Tech Discussion & Timeslips' started by Silver'nStripes, May 14, 2018.

  1. Silver'nStripes

    Silver'nStripes Junior Member

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    So, I installed adjustable valve shocks in my 2006 GT and I'm looking for some tuning advice. I took the car to the track and made a few adjustments, but I'm not sure I'm on the right track. My 60 ft. time improved some, though I think more due to tire pressure adjustments, and it's still slower than with the stock shocks, though I've eliminated some nasty wheel hop.

    Here's my setup:

    Engine:
    4.6L V8 with 5.0L stroker kit
    2.8L Kenne Bell Mammoth, 13 psi boost
    540 rwhp, 500 rwtq

    Shocks and Springs:
    2013 Cobra Jet Drag Spring Kit front and rear
    Strange single adjustable shocks in the front
    Viking double adjustable shocks in the rear, AJ valving

    Rear Suspension:
    Adjustable Lower Control Arms
    BMR Lower Control Arm Drop Brackets (bottom hole)
    BMR Adjustable Upper Control Arm w adjustable mount (bottom hole)

    Tires:
    Mickey Thompson ET Street
    26x10.5-15

    Run 1:

    2.152 60 ft
    Shock Settings:
    Front - 2
    Rear Rebound - 6
    Rear Compression - 10
    Tire Pressure - 20 psi
    Launch RPM - 2500

    The car spun pretty immediately. It looked to me like the front didn't came up very much, so I softened the front extension. The rear also seemed to drop and then come back up, so I increased the rear compression.

    Run 2 spun really badly, so I dropped the tire pressure and went again.

    Run 3:

    1.902 60 ft
    Shock Settings:
    Front - 0 (Lowered from 2 on the first run)
    Rear Rebound - 6
    Rear Compression - 12 (raised from 10 the first run)
    Tire Pressure - 15 psi (lowered 5 psi)
    Launch RPM - 2500

    The launch felt a lot better, it still spun. A little bit at first, and then a lot by the time I got to the top of first gear. Decided to stiffen the rear shocks some more since that seemed to help.

    Run 4:

    1.902 60 ft
    Shock Settings:
    Front - 0
    Rear Rebound - 8 (raised from 6 on the previous run)
    Rear Compression - 14 (raised from 12 on the previous run)
    Tire Pressure - 15 psi
    Launch RPM - 2500

    Pretty much the same results as the previous run. The best way I can describe it is it spun a little bit off of the line, and then progressively more throughout first gear, until I feel like I need to pedal it near the top of first gear.

    Overall, I'm not sure if my shock adjustments made that much of a difference. It seems the tire pressure made the biggest change in 60 ft. time. The car attitude seemed to improve, but the 60 ft time didn't follow. Perhaps there was too much tire spin for it to really make a difference? I'm also not sure if the front is coming up too quickly on the 0 setting.

    I'm also aware that I'm running a lot of anti-squat with the upper and lower control arm brackets in the rear. Could this be problematic? I'm also pretty sure that a taller and wider rear tire is in my future, probably 28 inches.

    Thanks for the long read, I really appreciate any insight! Even if you think I"m on the right track tuning-wise and I just need to keep after it that would be great to know.
     
  2. RocketcarX

    RocketcarX 95% of my weight is fuel

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    The car is immediately unloading the rear tire, almost instantly. The 2nd video shows it quite clearly the rear end is jumping up right after you hit the tires.
    The weight isn't staying transferred for long enough to get you through the 60 foot. With that suspension the car should leave like a dog running full tilt tucking his ass under.
    I would move the control arms up one hole in the relation brackets. Leave the front shock full loose and focus on the rear shocks. You want to encourage the front to stay up and the rear to stay down. So it looks like you need to slow the rear end down. I think you are going the wrong was with the adjustments if I understand them right, you want less compression resistance and more rebound resistance to hold the weight of the car over the rear axle.
     
  3. travelers

    travelers Senior Member

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    What gears do you have in the rear and what's you speed in the traps? Rocketcar is correct on the rear shock adjustments. You also need some one to film your car standing next to it so you see the side and back. Witch MT ET Streets are you using?
     
  4. Silver'nStripes

    Silver'nStripes Junior Member

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    You're completely right. I looked back at the recommended settings from Viking, I dialed in the rebound and compression backwards. :( Guess this means I have to go back to the track! I'm going to see about switching LCA positions this weekend.

    I have 3.55's in the rear. My personal best pass was an 11.74 at 117 mph last October. It had some more in it, but I wasn't able to repeat. I had absolutely horrendous wheel hop too, which is why I added the adjustable shocks. In the passes from these videos the mph was around 115 or 116.

    The ET Streets are 26 x 10.50-15LT, basically a DOT bias ply slick.
     
    Last edited: May 16, 2018
  5. travelers

    travelers Senior Member

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    Is your car a stick?
     
  6. Silver'nStripes

    Silver'nStripes Junior Member

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    Yep. TR-3650 with a McLeod RXT clutch and aluminum flywheel.
     
  7. 46addict

    46addict 13726548

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    Were you wheel hopping even with LCAs and relo brackets? And those are nice numbers. Was that on the same 13psi setup?
     
  8. Marble

    Marble forum member

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    Track prep seems horrible, just initial impression.

    How old are the tires?

    My car with the stock was into the high 1.4 with a similar set up. I would launch near 4500-5000 on a two step.

    My shocks were full firm in rear, full loose in front. Tire pressure at 16.

    I would check your IATs as it seems at your power level you should be trapping in the 120s.
     
  9. Silver'nStripes

    Silver'nStripes Junior Member

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    Yeah, that was with the same setup on stock shocks and springs. Found a video from that night.



    The prep was pretty nonexistent until later in the evening. It looked like some faster stuff was going to be testing for an event the following day, I was hoping they would have prepped a little extra.

    I think the tires are 2 or 3 years old, they probably have 10 or 15 passes on 'em?

    The best 60 foot I've gotten so far was in the low 1.60s or high 1.50s I think. I can't imagine launching that high and not completely roasting the tires. Guess it's worth a shot!

    When you say full firm in the rear, do you mean on compression or rebound? Or were they single adjustable?
     
  10. Phil

    Phil forum member

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