Shock Tuning Help

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

  1. Silver'nStripes

    Silver'nStripes Junior Member

    10
    0
    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

    2,502
    135
    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

    2,925
    59
    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

    10
    0
    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

    2,925
    59
    Is your car a stick?
     
  6. Silver'nStripes

    Silver'nStripes Junior Member

    10
    0
    Yep. TR-3650 with a McLeod RXT clutch and aluminum flywheel.
     
  7. 46addict

    46addict 13726548

    1,780
    53
    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

    668
    14
    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

    10
    0
    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. bunits19714

    bunits19714 forum member

    278
    25
    Need to move your lowers to middle hole like mentioned above, check specs on the upper for the 05-10, I believe you have the rears #'s reversed you need about 6-8 on the compression and about12-14 on the rebound to keep from unloading the rear tire. would of been nice to have dbl adj fronts so you could control the front coming back down- what numbers do Viking call for couldn't find aj valving in just a shock usually aj valving is coil overs- run the fronts full loose to get weight transfer(what does strange suggest) I am use to dialing in dbl adj fronts.
     
  11. Silver'nStripes

    Silver'nStripes Junior Member

    10
    0
    Finally getting back to the track this evening! (Thanks grad school)

    I used that super nifty spreadsheet to help reconfigure the rear control arms. Using the lower holes on both upper and lower brackets I was running ~150% anti-squat (!!!). Certainly helps to explain the launch behavior.

    I put the UCA in the top hole, and the LCA in the middle hole, based on the spreadsheet I should have ~115% anti-squat now. It feels a lot better on the street (ie doesn't punch you in the kidneys when you go over a bump, hooks up much better with the slicks on), I'm hopeful for good results tonight.

    Thanks everyone for the help, I'll post results when I can!
     
  12. Sactown

    Sactown Sactown

    5,201
    23
    IMO the rears are not nearly stiff enough on the compression, and have way too much rebound. If you watch my car launch (I consistently cut low 1.3 60s) the back of my car hardly moves, and the front doesn't even come up.

    Good luck tonight!







     
    dark steed likes this.
  13. ApexRaceParts

    ApexRaceParts Official Site Vendor

    274
    4
    Were you able to get back to the track? I know it sounds silly, but have you confirmed that the car isn't smacking the bump stops when it compresses and then jumps back off them? I would basically reverse the settings that you used on run #4, along with the new LCA angle, and see what she's got.
     
  14. Silver'nStripes

    Silver'nStripes Junior Member

    10
    0
    I did! I have a few launch videos that I've been meaning to get on YouTube so I can post them up here, but obviously I haven't gotten that done yet.

    I definitely made a move in the right direction. I ended up zeroing in on this setup:

    Front - 0
    Rear Rebound - 18
    Rear Compression - 2
    Tire Pressure - 13 psi
    Launch RPM - 2500

    My 60 ft. on that run was a 1.56, my best with the car. The launch still wasn't perfect, the rear tire took one wheel hop as the car left, and there is a LOT of body separation in the front. I'm hoping if I tighten up the front shocks a little bit and increase the rear compression it'll clean that up. The car went an 11.91 at 119, which isn't too bad!

    The next pass didn't hook very well, but I went through the traps at 121, which was my best mph by far to this point. Definitely a step in the right direction!

    I'll try and post the videos today...
     
  15. Silver'nStripes

    Silver'nStripes Junior Member

    10
    0
    Finally getting a chance to post some videos!



    1.834 60 ft
    Shock Settings:
    Front - 0
    Rear Rebound - 10
    Rear Compression - 4
    Tire Pressure - 13 psi
    Launch RPM – 3500

    I started with the recommended settings from Viking in the rear (for real this time). Still didn’t do so well. Lots of wheel hop and spin, clearly.

    Tightened up the rebound quite a bit and went way soft on the rebound and things improved quite a bit.



    1.560 60 ft
    Shock Settings:
    Front - 0
    Rear Rebound - 18
    Rear Compression - 2
    Tire Pressure - 13 psi
    Launch RPM - 2500

    I’m still getting one bad hop, but after that it seems to me like the rear fender gap is pretty consistent. The front fender gap looks pretty big to me. Perhaps too much?

    Like I said before, this pass was the best 60 ft. to date, so hopefully I'm moving in the right direction? I'm thinking if I tighten up the front shocks a little bit I can control some of the extra body motion and increase the rear compression to get rid of the last bit of hop I might pick up a little bit more time. What do you all think?
     
  16. psfracer

    psfracer billy badass Staff Member S197 Team Member

    10,906
    64
    You raced Travis lol? How could you hear yourself even think? Your car looks great - 8.80 still your best? Pretty awesome. I love Sacramento. Only been there a couple of times but the crowds are great there.
     
  17. psfracer

    psfracer billy badass Staff Member S197 Team Member

    10,906
    64
    I think you got some good advice in this thread - it's good you are tracking your results and know all of your settings from pass to pass - this is key.

    I saw it mentioned already once above - but don't overlook the tires. Once the rubber is too old -- they just don't work the same. I wanted to try out a different size slick once, so I put some used ones on that only had a few passes, but they were 3 years old. Spun every pass. It would initially hook, but then spin about 20 feet out every time. Got some new ones and hooked every pass, no other changes.

    I agree with Sactown - the rear of the car should leave pretty flat - here is a vid that has a bunch of launch clips from my old set up - you can see the rear doesn't really move any - best 60' was 1.24

     
  18. Silver'nStripes

    Silver'nStripes Junior Member

    10
    0
    I'm hoping to scrape together some spare change this winter to get some fresh rubber on the rear, thinking of going with the a set of Hoosier Quick Time Pros, 28 x 13.5-15LT. I think I've seen someone on this forum fit something similar in size under their car.

    The video looks great! What size rear tires are you using?

    The slow motion shot at 2:39 looks really cool. Almost no rear movement when the car launches, but then at 2:42 it looks like there's a good bit of rear fender separation. How much anti-squat are you running? Are you still using a 3 link setup in the rear?
     
  19. Silver'nStripes

    Silver'nStripes Junior Member

    10
    0
    Those look great! Something to aspire to for sure.