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Old 05-03-2005, 01:23 PM
NOF (New Old Fart)
 
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4 Link Angle and Bar Lengths

I'm building a 23 T Bucket with a 650hp 427 Side Oiler.

From what I gather I assume it'd be best to set the top rear link bars at an angle of 6 to 8 degrees upward from the axle to the frame. My top bar is 18" and the bottom bar is 20". The bottom bars are parallel to the ground and in line with the frame rails.

Can you guys who use a 4 link set-up tell me what set-ups have worked best for you at the strip in a real situation. What are your bar lengths and angles?

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Old 05-05-2005, 01:32 AM
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ok .... here goes it :

link bars ahve to "meet" someplace in space ... as if both bars are infinatly long and this imaginary point should be someplace in the middle of the car

drawing a line from where the rear tire meets the ground, thru where the bars "meet" and to dirrectly above the front tires gives you a visual idea of the amount of antisquat the rear suspension has

less then 100% antisquat and the bac end drops during a launch
exactly 100% and the back end stays level on launch
more then 100% and the rear end of the car pushes up

the so if you take the car to the track and the tires just spin on launch , add some more antisquat by repositioning the formard ends of the bars

theres realy no way to set up a car right in the garage, its just a case of getting it close and taking the car to the track to try it out, this is why a REAL bar setup from jegs or such has such a rance of attachment points on the frame and differential

see attached pic ... sorry for the quality, i dont have a scanner, just a webcam
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Old 05-05-2005, 03:35 PM
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If you have excel you can try using this:
http://home.earthlink.net/~triaged/F...arLinkV3.0.zip

I have put all the formulas into it so it will calculate the ammount of Anti-Squat that you have (along with a bunch of other things).

If you want to read more about it try here:
http://www.pirate4x4.com/forum/showthread.php?t=204893

Edit:
The eXtreem4x4 show on Spike TV will be doing a show sometime soon that will use the calculator that I made. I think they are just about done finished with editing it.
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Old 05-05-2005, 06:08 PM
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Quote:
Originally Posted by Triaged
If you have excel you can try using this:
http://home.earthlink.net/~triaged/F...arLinkV3.0.zip
that needs to be put in a new thread and titled appropriatly, then stickied

thats the hotness right there
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Old 05-05-2005, 06:42 PM
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I'm glad you like it. I have put a bunch of work into it. I could start another thread but are there enough people here that design and build their own triangulated 4-link suspensions to warrant making it a stickey? There have been a bunch of guys that have used it to design triangulated 4-links (all it does at the momment) on that sight I posted.

The biggest problem still remains finding (guessing) the Center of Gravity...
In the text file that is in the zip file there is a link to a site with an excel file to calculate your CG.
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Old 05-05-2005, 11:50 PM
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To expand on Triaged's comments, you can determine whether a car is going to squat or rise by the position of the "instant center" relative to the no squat/no rise line. The instant center location is the point where lines through the upper and lower links intersect, as viewed from the side. The no squat/ no rise line passes through the rear tire patch (actually, about an inch below) and through the intersection of two other lines, one a horizontal line through the center of gravity and the other a vertical line through the front tire patch. Normally, I would, at this point, simply say that, if the IC is above the no squat/no rise line, the rear end of the car will rise on launch; if below, squat, but TBucket's geometry probably places the IC behind the rear axle so I have to add a few more words. When the IC is behind the rear axle, the effects are reversed. That is, a point above the line will cause the car to squat and vice versa.

Whether a car squats or rises has absolutely nothing to do with the weight transfer. That is determined solely by the acceleration and the location of the CG. If the car squats or rises, however, it will cause an oscillatory loading as the rear of the car bounces up and down.

And, it is definitely possible to "tune" a rear suspension for launch while the car is in the shop and the engine off. You simply place wheel scales under the front wheels, prevent the engine from rotating, and then pull back...with a "come-along" or similar device...on a chain attached to the roll cage at a height roughly equivalent to the CG height. By determining how evenly the loads are being removed from the front wheels, you can determine what is happening at the rear.

An accurate measurement of the CG height is only necessary if you're trying to intersect the no squat/no rise line near the rear wheels. I wouldn't recommend trying to do this as the suspension then becomes sensitive to roadsurface irregularities and changes in such things as fuel load. If you place the IC far enough forward, a rough "eye-balling" will usually suffice for a CG height number. In fact, for TBucket, I would recommend that BOTH upper and lower links be set at an angle having a tangent equal to the CG height divided by the wheelbase. Suppose, for instance, that the CG is estimated to be at 25 inches and the wheelbase is 100. That would make the tangent equal to 0.25 and a scientific calculator tells me the angle would be 14 degrees. That would give you a car that neither squats nor rises. (Parallel lines meet at infinity.) If you then wanted to cancel the driveshaft torque (unloading of the right rear), you could increase the right side angle and decrease the left by the same amount.
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Old 05-06-2005, 01:27 AM
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You guys have been a wealth of information here.

Thank you
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Old 05-07-2005, 05:05 AM
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Quote:
Originally Posted by BillyShope
-snip-
very good info to have, and it makes sense that the come along @ cg would show you how the suspension responds

i know my basics on alot of stuff, to the point that my car buddies always wind up asking me for help on almost anything, but my fellow members here school me good whenever im on
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Old 05-12-2005, 11:32 AM
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This is the 4-Link I am using on my '47 Chevy Fleetline










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Old 05-12-2005, 11:39 AM
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nice pics

Nice pics but that's a 4 bar not a 4 link.

The lower bars are set parallel to the frame. The length of the 4 bars are adjusted for the desired wheel base. The upper bars being the same length as each other. The same for the lower bars. The desired wheel base dictates where the shock mounts are located for proper suspension. The upper bars are located for instant center which has already been discussed.
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Old 05-12-2005, 11:41 AM
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Whoops. thanks!

I did not know there was a difference between 4-link and 4-bar.
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Old 05-12-2005, 12:06 PM
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4 link

Here's a pic of a 4 link.
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Old 05-12-2005, 01:04 PM
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And the differance is?
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Old 05-12-2005, 01:10 PM
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Far as I'm concerned, you can call them whatever you like, but it seems to me the more common name would be "triangulated 4link." Art Morrison sells what he calls a "4bar" setup and that's what I've been using as my definition. Art's 4bar has brackets which hold the link pair parallel under all circumstances. You then adjust the front bracket up and down to control squat, but, again, the links in each pair are always parallel. (This means it'll never bind during street driving.) So, when I mention a "4bar," I'm referring to Art's package or something like it and when I mention a "triangulated 4link," I'm referring to something like pictured in this thread.

And those are gorgeous pictures! Ain't digital photography wunnerful!!!
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Old 05-12-2005, 04:02 PM
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4 link

The pic I posted earlier is from Art Morrison's website. It says 4 link right in the corner.
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