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 Post subject: newbie with 4 link ??
 Post Posted: Sun Aug 10, 2008 10:34 pm 
 
All right guys, please give me any advise you can spare, I am a novice with 4 link adjustment.  I bought car several years ago, put 605 engine from top dragster went 7.90’s (5.0’s) always went straight and was overall happy.  Was afraid to tweak 4 link for fear of messing up setup.  All I changed was to make rear tire weight pretty equal and neutralize anti-roll.
This year built 706 that makes 1270 HP, 1035 ft/#’s.  This added about 100#’s to car, now runs the same as above.  
Car used to squat a little and tote the front tires to the tree.  See this video http://www.youtube.com/watch?v=iDNccGXgMYk.
Now it does neither one. See this video http://www.spradlinmotorsports.com/photos.htm. (click blank box) Also added quikdata logger and you can see spin in below graph from first run on video.  Several runs and all graphs and ET’s the same.  First and second run I forgot to neutralize anti-roll so caused it to drive left out past the tree, fixed this for 3rd pass.

http://www.flickr.com/photos/spradlinmo ... 2751576973

Also is there a free program out there for IC’s.  I’m using the attached file I found for 4 wheelers, I think it works OK.  Note that the CG height is estimated at this point because front struts are at Lamb getting rebuilt/revalved.

The below specs are how it was set up in video.  Right know struts are coming back from Lamb because adjusters were stuck, they revalved for current setup ($$!).  Also new springs all around coming.  275# upfront, 110# out back.

Car Specs.
WB:111”
Weight: 2559#
LF: 762#       RF: 586#
LR: 557#       RR: 654#
Front: 53%
IC: 63” out, 5.25” up
Bottom bar: 2* down
Top bar: 13* down
Front separation: 6.875”
Rear separation: 10.5”
Pinion <: 2.5*
Front springs: 235#
Rear Springs: 110#
Rear shock setting: 5 clicks off tight (12)
Wheelie bar height: 6.25”/6.5”
(It is only 48” as well, plan to make new as soon as time allows)
This was first pass on M/T 16-33.5’s with 6# air.  Video shows they wad up pretty good so going to try 6.5#.  After looking at video closly I think wheelie bar is hitting to early and limiting travel. ??
2 step RPM: 3800

Questions:
Should I lower pinion angle?
Bob Mandell of Bob’s ProFab suggested the 275# shocks b/c of front weight and to raise IC up but leave same distance.  What’s your thoughts?
I can tell from the video that it needs to bring front up more like old motor.  What will accomplish this?
Once get parts in, I will rescale and even rear, what front stagger is ideal?
To raise the IC height I can do two things: Lower axle end of bottom bar making it pretty much level (IC: 52.3/7.3) or raise opposite end (IC: 49.3/8.2) however some structural bars prevent me from raising track bar with this so it will have to say on original hole.  Someone told me this is no problem, but I have read on here some different views.  What’s your take on this again?
What should front shock setting start with?  2 clicks off tight?

Help reading the graphs: Once it hooks, it makes a lazy “S” on shaft graph, what does this indicate?

Thanks for any advise you guys have.

Casey


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 Post subject:
 Post Posted: Sun Aug 10, 2008 10:37 pm 
 
sorry guys the graph link didn't work.

Image

I tried again above, if didn't work please tell me how to attach pics.

Also please tell me how to attach files to post.  (for 4 link program)


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 Post subject:
 Post Posted: Mon Aug 11, 2008 8:11 am 
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Casey first of all, welcome to MSV!  

Concerning the pic you linked to, the code for the pic is correct on your post so the only thing I can think of is that the site that hosts your pic doesn't allow link connections from other sites?  You might check with them to see if this is the case and or find another hosting service.

We don't host uploaded files for the same reason we don't host pics.  We just don't have the server space available!  Hosting pics and files would probably quadruple the size of the database, and the hosting price an equal amount.

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 Post Posted: Mon Aug 11, 2008 8:36 pm 
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Casey I just got home from a 14 hour day. Don't loose faith. I or someone will answer your questions asap!


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 Post subject:
 Post Posted: Mon Aug 11, 2008 9:00 pm 
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I'll take a stab at a couple of'em.

MT tires?  O:)  Well, not enough air for one thing.  Did you check the tire with a heat gun to see if it's near the same temp across the tread?  My car with similar rear corner weights liked more air, up around 8/9 pounds!

That lazy S you speak of is the tire unloading and then loading again.  Might be that the suspension is reacting too fast in which case a few more clicks on the shocks might help.  

I noticed you have some tire spin down track as well.  What weight springs are in the rear now?  With that much weight on the rear corners, I'd think that a 110 is too light?  Just put a pair of 125s on my car and it took a large amount of tire spin out of high gear!!  Here are the graphs from a couple of my runs, before and after.  

http://motorsportsvillage.com/forum/vie ... 7&start=90

Are the rear shocks bottoming out?  Mine were with a 95lb spring and a 3/4 inch wickerbill on the rear wing.

Moving the IC down will soften the hit on the tire.  Moving it up will make it hit harder.  IC length in and out mainly affect the speed at which these things happen along with longer ICs will tend to lift the front more.

I'll think on this a little more and may post additional stuff tomorrow.  Oh, and you have a PM!

Next!!

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Necessity is the plea for every infringement of human freedom. It is the argument of tyrants; it is the creed of slaves.

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 Post subject:
 Post Posted: Tue Aug 12, 2008 9:44 am 
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OK, I'm going to take a stab at the pinion angle thingie and if someone has more/better info, then please feel free to chime in.

Pinion angle on a 4 link isn't as much of a deal as it is on a ladder bar car.  Reason is that the housing on a ladder bar car actually rotates with suspension travel whereas the 4link will stay near static setting in dynamic conditions, ie, the housing doesn't rotate as much with up and down motion of the chassis.  Ladder bar cars usually set pinion angle down for that reason as the ideal condition is that the pinion be straight with the driveshaft.  

Any angular movement in the U joints creates friction which costs HP.  In theory, the angle of the pinion should be exactly the same as the output shaft of the transmission, ie, those two lines should at least be parallel with each other and directly in line would be excellent.  A drive shaft with two U joints actually speeds up and slows down twice a revolution when it's running at any kind of angle so if the angle of the pinion and the tranny are different, harmonics are created which also cause friction and power loss.  

Now, back to the pinion angle thingie again.  What happens under load is any chassis flex in the rear will allow the pinion to move upwards slightly even on a 4 link chassis.  This is the reason ppl put some down angle in it as under load there will be some slight flex upwards from torque reaction of the rear housing at the hit and down track.  I've heard different numbers but I'm thinking that about 1 maybe 2 degrees would be plenty in most cases.

Oh, and do a search on the site for "pinion angle" in this section and you'll find a LOT of discussion that has already taken place on this topic before.  
;-)

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 Post subject:
 Post Posted: Tue Aug 12, 2008 9:57 am 
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I think it's been discussed here before but pinion angle will not change they way a car hits the tires. Like Ken said there is some slight hp loss if the angle is off. I have always tried to set up 4-lnk cars with 2-3 degree pinion angle and ladder bar cars 3-5 degree of course this a downward angle on both applications.

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 Post subject:
 Post Posted: Tue Aug 12, 2008 2:38 pm 
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Tire pressure. Pretty much as Ken says. Sounds like pressure is low. The story don't stop there. The needed tire pressure can change from car to car, even with same size and brand an compound. Several things can effect this. First rim width. 2 power level, (gear effects this to), 3 instant center values, 4 car weight and how much weight is transfered and how fast due to center of gravity hight and spring rate,5 how good is track.

The best time to check temps would be after a launch. On a burn out wheel speed is up and won't give the same reading. Also you can get a fair read on pressure by starting on low side and watching 60s raise pressure till you go slower , then back off some.

Pinion angle. Try to make angles the same but opposite at tail shaft as rear end. 1 2 3 degrees anything but straight. Lack of angle sets up bad harmonics. This causes loss of power and premature wear on joints, tail shaft bushings and rear end. Pinion angles used to be important on leaf cars, where they changed and was checked with snubber or bars or slapper bars. You just want to make up any slop or bend in a ladder or 4 link car. That shouldn't be much.

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 Post Posted: Tue Aug 12, 2008 5:43 pm 
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 Post subject:
 Post Posted: Tue Aug 12, 2008 5:43 pm 
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 Post subject:
 Post Posted: Tue Aug 12, 2008 10:38 pm 
 
thanks so much guys, keep it coming!!  is the bickel book any good?


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 Post subject:
 Post Posted: Tue Aug 12, 2008 10:57 pm 
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It's pretty good.
I think I would Pick Rick Joneses book over it.


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 Post subject: I'm Baaack!!
 Post Posted: Thu Oct 09, 2008 10:49 am 
 
hey guys thanks for your help.  I made a gear change from 3.89 to 4.30 and it will pull the front tires now.  see need some minor fine tuning.  At jackson, SC race it was driving RIGHT down low and I made a bar change and it corrected.  then at atlanta where track was very bad it was driving LEFT so a combination of bar change, wheelie bars, and lining up differently made it drive straight.  So please take a look at these drive shaft graphs and tell me what is happening in them, I haven't had this computer stuff untill this year and don't know what it is telling me.

also videos are at

http://www.spradlinmotorsports.com/photos.htm

these have regular speed/40%/5% for your viewing pleasure.  I uploaded so they could download at a decent speed.  if quality is not good enough let me know and I will upload differently.

Jackson
SATQ1
drove staight but had wheelie bars all the way up from trying to get it to leave before gear change.  but best pass of weekend, so maybe this is good but I thought generally nose up hurt ET.

60'- 1.080 (I think on back tires here)
330'- 3.154

Image

SATQ2
brought wheelie bars down and started driving RIGHT

60' - 1.088
330'- 3.193
wheelie bars- L-6"  R-6 1/4" hitting both hard

Image

SATR1
moved bars up but still dring RIGHT

60'- 1.094
330'- 3.193
wheelie bars- L- 7 1/8" R- 6 5/8" rode right a little and left just a touch so I think this is right height

Image

SUNQ1
made a 4link change and drove straight
before                           after
724#    624#                 732#           624#
605#    617#                 597#           624#

60'- 1.082
330'- 3.180
wheelie bars- same as above

Image

SUNR1 (no video)
for some reason drove right again, shun hard

60'- 1.102
330'- 3.202

Image

ATLQ1  (no video)
same setup as above, drove LEFT first and then I either over corrected or I was steering in the air and when came down goes RIGHT quick and then I steer back LEFT??  Other cars were having handling issues as well.  chattered tires about 10 feet out, first time ever felt this in door car.

60'- 1.114
330'- 3.213
wheelie bars- rode right hard and nothing on left

Image

ATLQ2
brought right wheelie up to match left so that it wouldn't drive car right with wheelie.  lower leaving RPMs for 4200 to 4000 to try to stop spin.

60'- 1.117
330'- 3.209
bars- 7 1/8" didn't touch at all

Image

ATLR1 (no video)
made a 4 link change to take weight off right tire.  lowered wheelie bars 738#        621#
668#        560#
still drove left, riding on right wheelie some and on left just a touch.

60'- 1.117
330'- 3.211
wheelie bars - 6 5/8" square

Image

ATLR2 (no computer data)
lowered left wheelie and this pass was straigntest of weekend.  also tip from Kurt Damron to line up on right side of grove in left lane because the lane drives you right.  all these things combined seemed to work.  even thought 60' doesn't show it, the 330'/660'/1000' was fastest of weekend.  I quess cause I was not doing all that sashsheying. But have no computer data to know what a good run is :(.

60'- 1.117
330'- 3.207
wheelie bars - L- 6 1/8" R-6 5/8"

ATLR3

spun and went left again BUT trans pump bolts were loose and leaking pretty good, TQ was slinging fluid I believe and caused me to spin.

60'- 1.120
330'- 3.221

Image

thanks guys I know this is a lot of info.  but if nothing elso just look at the graphs and tell me what is happening and causes.  Like what causes the step.  Is the intial wheelie bar hit present?  what causes the lazy "S".

For both of these races the M/T were on 7#, should I have lowered it at ATL to help with spin?

thanks a bunch.


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 Post subject:
 Post Posted: Thu Oct 09, 2008 12:18 pm 
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My time is limited right now but I looked at the first video. Rebound/extension of the shock was too soft. Watch the rim at trans brake release. stiffen up atleast 3 clicks.

Bump/compression was too stiff. soften up a few clicks.
If both of these adjustments are close to their limit then move the lower 4link bar down 1 to 2 more degrees if your still at 2 degrees.

Wheelie bar adjustment. If it is the bars driving it one way or another I'll tell you the easiest way to remember which way to go.

Think if the wheelie bars and the rear tires like an "X"
When the Right wheelie bar hits the track it loads the Left tire. and vise versa.

So lets say the car is drivin left. That means the left bar is putting more pressure on the right tire. You would either raise the left bar or drop the right.

Make sense?


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 Post subject:
 Post Posted: Thu Oct 09, 2008 1:33 pm 
 
thanks,

the bottom 4 link is level right now.  

the compression is 7 from tight (out of 12)

the rebound is also 7 from tight (out of 12)

Also it seems to move a few feet before front end lifts, is this normal?


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