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 Post subject: 4 link bar angles?
 Post Posted: Sun Apr 04, 2010 6:50 pm 
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What is the effect of raising the bottom bar of a 4 link at the rear to get a better bar angle?

I have to raise it up one hole in the back to get the bottom bar around 4 degrees down angle.

This car was originally built in the weeds with a smallblock in it and when I put a big block in it I had to raise the front end to get oil pan and header/tire clearance and then that meant raising the ride height in the rear. Doing that made the bottom bar of the 4 link level, or slightly running up hill.... ](*,)

I think the instant center must be right around the neutral line like that, because the last two weekends I run it, it doesn't show any body movement to indicate squat or anti squat. It looks to me like it hooks initially due to front end weight transfer, then as I drive out in low gear it bounces and hooks, then spins, then hooks then spins slightly.

Here is a video of a pass. It didnt do it very much on this pass. Sometimes its bad and sometimes its not.

http://media.photobucket.com/video/maso ... 5.flv?o=15

I lowered the car 1 inch in the rear tonight and the bar angle is 4 degrees now, but I raised the lower rear end up 1 hole and have another to go yet.

How does that effect it? Less leverage?


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 Post subject: Re: 4 link bar angles?
 Post Posted: Tue Apr 06, 2010 8:07 am 
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Hey Mopar guy,

I'll see if I can help out a little bit, although I am a chevy guy \:D/ =;

Ok, from what I see, the front end does porpoise a little bit which means the front & rear shocks are fighting each other, and IF, you have double adjustable rear shocks, I would take some compression out if it, say 1-3 clicks(but 1 click at a time per pass per side) then see what your 60 ft et does. Do you footbrake this car? it sounds like it, and what rpm do you come off the line at? I have seen some Savoi's(spelling) with hemi's in them that just jack up about 2-4 inches when they preload there suspension and then leave the line, but they still have leaf springs too! \:D/

It looks like you are just a little stiff in the rear, try to let it move a bit and see what happens and write doen all your info as to not get lost from what you had.

The bottom bars, by changing the I/C in your chassis vs the neutral line, which in your case from what your saying, will give you an I/C that is farther out forward, and below the neutral line (I am guessing here without knowing where your new I/C will be with the changes you have made), and you should be taking a little bite out of the rear end, but again, without knowing where your I/C is in relation to your Neutral line, it is a little difficult to know exactly what will happen unless you are a seasoned chassis tuner, but from what I know is,(which isn't much) :- if your I/C is below the neutral line, the chassis will tend to move off the line with less hit in the rear and less lift in the front, this also depends on the power of the engine also, just another variable to figure in(what et's and 60 ft's do you normally have?) and, if you raise the I/C above the neutral line, you will tend to hit the rear harder, and lift the front end a little more but, it also depends on how far forward, or back your I/C point ends up at! This is why you need to know where your I/C is at all times and haveing a baseline setup written down to always go back to if you get lost with tuning, and more times than none, you will get back to being prety close to where you want to be,but not always. I have some info for you to read, and I will send it in a pm ok?

Testing by trying is the best way as know one can adj. YOUR chassis over the phnoe or net, and this can be dangerous if not taken care in tuning. Good luck and jump in guys if I am way off base with my info, I am still learning also.

John

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 Post subject: Re: 4 link bar angles?
 Post Posted: Tue Apr 06, 2010 10:06 am 
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Thanks for the Help Elky.

Yes I do footbrake it at around 2800 RPM on the line. If you watch the Video you will notice I have quite a bit of front suspension travel. It still has the stock torsion bar front end on it.I should have mentioned that in my origional post. It is a iron headed big block so its nose heavy 45 rear 55 front weight bias.

You know now that you mention it, when I raised the rear of the car I bet I moved the IC above the neutral line. I had the shocks set loose (2 clicks) a few weeks ago and it was really bad and I started tightening them up and the 60 ft got alot better. Probably throwing all the shock in it is what helped it then.

I think I am at 6 clicks now so its pretty stiff like you said, so I am going to try loosening them up Saturday at the TNT.

I lowered the rear of the car the other night so I moved the IC down again. Maybe that will help my situation even more.


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 Post subject: Re: 4 link bar angles?
 Post Posted: Sat Apr 10, 2010 7:13 pm 
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Did some more testing today at Mason Dixon and even with the new slicks the car was junk off the line the first 3 passes then I moved the top bars up one hole in the front to move the IC further forward and that did the trick.

http://s892.photobucket.com/albums/ac12 ... ass003.flv

Didnt spin a lick the rest of the day.

I want to try them up one more hole next TNT. Starting to hang the tires now.


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 Post subject: Re: 4 link bar angles?
 Post Posted: Sun Apr 18, 2010 5:34 am 
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How are your 60 ft. times doing? Looks a lot better on the hit, good luck this season also.

John

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 Post subject: Re: 4 link bar angles?
 Post Posted: Fri Apr 23, 2010 7:50 am 
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60 ft was 1.42 after I made the bar change.

I have the engine out now fixing a cam wear problem I found and I discovered the front brakes were hanging up bad. If you watch the fronts in the video when it pulls the tires they stop for an instant.

Hopefully that will pick me up some more ET and mph.


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 Post Posted: Thu Jul 15, 2010 4:56 pm 
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I decided to make some changes to the suspension to try and make it hook up better on the hot tracks we are racing on now. It picks up a ton when the sun goes down and the track starts to cool. Have to have the shoe polish ready.

I plotted the 4 link out on the floor last night and I was surprised where my IC was at.

74" out and 4.5" up!?! Had no idea I was that far forward with it.

I moved the bottom bar back down to the bottom hole on the rear and that put me at 57 out and 8 inches up. Bottom bar is 2.5 degrees down right now.

This car is nose heavy with 55 percent of the weight out front. 111" wheelbase.

Compared to the IC I had originally that will make it hit the rear harder right?

I am also replacing the single adjustable Strange shocks with a new set of AFCO double adjustables.


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 Post subject: Re: 4 link bar angles?
 Post Posted: Thu Jul 15, 2010 6:30 pm 
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Those AFCOs have about 30 clicks lock to lock. I'd start out loose and sneak up on it if I were you. On mine I went to 15 on both thinking that would be a good starting point but not so, way too stiff and that caused the car to get loose down track. If memory serves, I'm only like 4 or 5 clicks now.

IC location is a crap shoot as there's no "exact" setting that will work for everyone, which is usually the case on most of this stuff. 77 inches sound a little long but then again, it might not be that bad on a nose heavy car. I guess you'll find out! ;-) That's the reason those rear suspensions are adjustable, hey!

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 Post subject: Re: 4 link bar angles?
 Post Posted: Mon Jul 19, 2010 9:56 pm 
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Didn't help the traction issues any. I am going to go off the deep end and set it at some serious anti squat percentage by moving the IC back and up and see if I get any chassis separation and go back the other way with adjustments if its too violent. This is where I set it at now.

IC length 46.68 IC height 10.48 and antisquat 134.46


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 Post subject: Re: 4 link bar angles?
 Post Posted: Mon Jul 19, 2010 11:21 pm 
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10 inches up sounds a little hight to me?? Both my light car and heavy car like LOW numbers there, ie, 2 and 4 inches but then again, both those are @ 50% rear weight or more.

On another note, Scott Smith likes 3* down on the bottom bar then work the top to get it to work the best. Mine are in that neighborhood.

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 Post subject: Re: 4 link bar angles?
 Post Posted: Tue Jul 20, 2010 9:03 am 
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Edit, the ICL n is supposed to be 45.37 the ICH 5.33 and that gives me an anti squat of 72.57.

Bottom bar angle is 4 degrees down.
Top is around 20 degrees down.

These Calculators only give you accurate numbers if you enter you figures in the RIGHT PLACE.

](*,) lol


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 Post subject: Re: 4 link bar angles?
 Post Posted: Mon Jul 26, 2010 11:30 am 
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Any feedback moparacer? How has it reacted?

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 Post subject: Re: 4 link bar angles?
 Post Posted: Wed Aug 11, 2010 10:35 pm 
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Elkyman wrote:
Any feedback moparacer? How has it reacted?



The only reaction I have gotten is a rise in blood pressure when I look at my time slip and see i am .03 .04 or even .05 off on the 60 ft and couldnt run the dial.

I finally gave up with suspension and shock settings and put a ballast box in the back and threw 150 lbs in it last race and it didnt spin a bit the whole day.

Putting new slicks on it for this weekend. Cant think of anything else it could be.


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 Post subject: Re: 4 link bar angles?
 Post Posted: Thu Aug 12, 2010 8:18 am 
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When you footbrake a car the front brakes are active. Whatever value of braking effort the front brakes are preventing forward movement by there is that value of ANTIDIVE in the front end. Stock car front ends have antidive. Mopars do it with the horizontal angle of the top A arm. Go look at it and you will see the line drawn through the pivot bushings is angled down towards the rear of the car, that is what the engineers call AntiDive. It holds the front of the car up under braking. When your braking at the start line with your foot on the throttle the front end is in AntiDive mode and the weight upon the rear axle is Reduced. Its sort of a 4 link in reverse. When you let the brake go the Antidive stops and the car collapses at the front end and then gets shoved forward so it rises again. The sequence is probably too fast to see. But have a think about that and see if you recon that could be something to do with porposing. ;-)
I cant view the video as I dont have the right thingy and Im not interested to fix it etc but Im just telling you something that maybe you didnt think about.


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 Post subject: Re: 4 link bar angles?
 Post Posted: Sun Aug 22, 2010 7:59 pm 
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Shinker any car I have ever footbraked the rear brakes do most of the holding when you are powerbraking while staging. If the rear brakes are not sufficient enough to hold the torque, you end up sliding the fronts through the lights.

I added another 50 lbs of rear ballast and took 5 degrees timing out of it last night and it didnt come close to spinning all evening. I just cant afford to fool with this thing and loose first or second round when it spins anymore this season.

I think my best option is to raise the engine and move it back over the winter to help the weight bias.


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