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 Post subject: Let's talk 4link
 Post Posted: Sat May 27, 2006 11:09 am 
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I just bit the bullet and did the calculations on my car's 4 link setup. The way the rear frame 4link mounts were installed won't allow me to move the IC any lower than 9 inches no matter where it is in length. I've only got one setting that showed up in "Dave Morgan's sweet spot" and it's 45.5 out and 12 up? I just checked the Studebaker and it's at 39.5 out and 2 7/8 inches above ground. The Camaro is at 56 inches out and 10.9 up now, which I don't think is far enough down and is too far out. I'd like to have it around 45 inches out and 5 inches up but don't have that option.

So I guess my question is, what is an average setting for other guys on here as far as IC goes? Is anyone else running the IC out as far as my Camaro is now?

EDIT: I just went back into the program and added to more holes to the bottom of the frame mount and it will give me everything I want or could need. I guess some chassis work is in my future, hey! O:)

Still want to hear some other ppls ICs though. \:D/

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Last edited by Ken0069 on Sat May 27, 2006 6:06 pm, edited 1 time in total.

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 Post Posted: Sat May 27, 2006 12:40 pm 
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I think what your going to find is a different I/C for each car works best.
Think of your car as a refrigerator. You want to push refrige across the room. Push too high it topels over forward, too low and It topels over backward (wheel stand). If you get just the right hight it pushes easy (less H/P to do same job. Now if we put a half side of beef in the top freezer, that point moves up (Changed Center of gravity). You need to move push point up. If you emptyed the freezer and top shelf with all the milk and juice(lowered center of gravity). Move push point down. If you worked out and was stronger and pushed harder, It would exagerate the syntoms (faster topples) This is why more H/P is harder to hook up.
Besides the holes that your linkage hooks to, you have ride hight to change that sweet spot. Think the rear mouting points will always stay the same, as long as you don't have a flat. the fronts will change with ride hieght changeing the I/C point. It also changes the center of gravity. Getting the right I/C can not only get you hooked better but give you back waisted H/P. Remember the distance out thr I/C is is not written in stone. If the 2 lines from bars split that Sweet spot, your looking for, It can be almost as good. The farther back the I/C point is the faster the reaction. If you could accuatly mesure the center of gravity hight it would make things a lot easyer. I had a formula to do this, by weighing cars rear at different hights but darned if I can find it. It's kind of like finding the hight of a tree useing angles and distance from tree. Maybe a math wizzard could step up here, been too long ago for me. For me the optimum is getting car to lift one tire and keep one in contact a little, and have minimal compresion or separation in both rear wheels. That transfers 100% of weight to rear and don't waste it on lifting front end.

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 Post Posted: Sat May 27, 2006 12:47 pm 
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Ken, I have a 108 inch wheelbase 69 camaro. I set mine where they said to start off and did not touch it for three years footbrakin. Changed it but had old tires at end of season and it hit the tires harder and stopped my small wheelies. With new convertor this year and alcohol it has wnet from 1.42 last season footbrakin to 1.30 this year . It is hitting the tire so hard now that I am folding them up and have a slight spin issue. But when it hooks the wheels are knee high or better. I have it set at 50.99 out and 4.46 of the ground. I too would like some input on this subject. =;


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 Post Posted: Sat May 27, 2006 1:41 pm 
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StrokerCamaro wrote:
Ken, I have a 108 inch wheelbase 69 camaro. I set mine where they said to start off and did not touch it for three years footbrakin. Changed it but had old tires at end of season and it hit the tires harder and stopped my small wheelies. With new convertor this year and alcohol it has wnet from 1.42 last season footbrakin to 1.30 this year . It is hitting the tire so hard now that I am folding them up and have a slight spin issue. But when it hooks the wheels are knee high or better. I have it set at 50.99 out and 4.46 of the ground. I too would like some input on this subject. =;


My car is 108 also. It doesn't pick up the front much at all off the Tbrake. Footbraking it seems to squat and go and doesn't spin that I'm aware of. The car will 1.27 to 1.29 60 ft depending on the track and hasn't done much better than that off the Tbrake @1.265 I can change it to 50 and 10 by moving the top bar down one hole on both ends. Moving the top bar down one hole in the front moves it back to 43.5 and 10.4

We're going to test again tomorrow at Piedmont, which is a really good track so I should have some more data after that. I may just leave it alone for now as tomorrow is testing on the carb swap I did yesterday. Went to one of my 750s instead of the Dominator. Once I get the fuel mixture right I'll concentrate on the 4 link.

Do you think you're hitting the tire too hard at 50 and 4.46? It's my understanding that if you raise and shorten that IC it softens the hit.

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 Post Posted: Sat May 27, 2006 4:35 pm 
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ken0069 wrote:
It's my understanding that if you raise and shorten that IC it softens the hit.

Ken,
Raising the IC or shortening the IC should increase the initial "hit" of the suspension and tend to make the rear suspension separate more at launch.

I have ladder bars so my IC isn't nearly as adjustable but is around 32" out and 6" high. My WB is 108 also.

Rick


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 Post Posted: Sat May 27, 2006 6:06 pm 
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Rick was going by the manual from Chassisworks that came with the 4link in the Studebaker. I re-read it and the quote is;

"as the IC gets shorter and higher, the chassis will tend to shock the tire slower"

This is why I said it softens the hit. I guess that was a poor choice of words for that event. I just interpreted the "slower" to mean "softer" which may not be accurate depending on how you look at it.

So, is my Chassisworks manual wrong?

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 Post Posted: Sat May 27, 2006 6:36 pm 
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Ken0069 wrote:
Rick was going by the manual from Chassisworks that came with the 4link in the Studebaker. I re-read it and the quote is;

"as the IC gets shorter and higher, the chassis will tend to shock the tire slower"

This is why I said it softens the hit. I guess that was a poor choice of words for that event. I just interpreted the "slower" to mean "softer" which may not be accurate depending on how you look at it.

So, is my Chassisworks manual wrong?


I've never heard it described in terms of faster/slower. The rate of the hit is controlled mostly by the shock. The amount of hit is mostly controlled by IC and gear/engine.

From my understanding, the way they word that is incorrect. A short/high IC will hit the tire more initially where a long/low IC will transfer more and hit the tire more as the car starts moving. High powered cars typically have very low and fairly long IC to reduce that initial hit.

Rick


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 Post Posted: Sun May 28, 2006 8:21 am 
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Rick I've been thinking about that quote and in one sense it does sound about right. If the IC is up and back it would tend to lift the body as well as move the car forward. In this case, it would actually slow the reaction of the car a bit due to the lost motion moving the car up instead of forward? Long and low IC would do the opposite. If the IC was ahead of the CG then it would tend to move the car quicker and not lift the rear of the car as fast, or at all. Of course it wouldn't hit the tire as hard either. Does this sound right? I noticed that anti squat % moves a good bit from one extreme to the other which is related to IC location as well.

You mentioned that high HP cars typically use a long low IC. That would explain why mine is as far out as it is now since the guy was runing in the 4.80s with it. I still think somewhere around 45 inches and lower than 10 will be where I need to go. Once I get the lean problem fixed that should tell me where I am on the suspension.

It's been so long since I did any of this I've actually forgotten what is involved. The last 4link adjustment I made on the Stude would have been in the first couple of months of racing it which started way back in 1994. Hummm, it's been 6+ years since I built an engine too? I may be in trouble =;

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 Post Posted: Sun May 28, 2006 9:31 am 
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I built my first 4 link in 69, but never understood them till way later in racing dirt ovals. the terms are a bit different, but slower and faster was a part that was mainly controlled by how far out your I/C was,More so than hight. On all cars, you have a neutral line going from center of contact patch threw center of gravity. The farther above or below the I/c is will determine if you get separation or compression and to what degree. farther up or down is more.
Lets say you was above the neutral line. The bars would want to lift the front mounting point,driving the tire under car and with the weight comming to the rear would put more presure on that contact patch. If your I/C was below the neutral line It will compress the rearby lowering the front mounting point. Less presure on tire contact patch. The farther above or below the more or less presure. I have put I/c back and so high that it loaded so fast it was uncontrolable and unloaded,(hopped like a bunny). And I have seen them so low the just burn tire even after front to rear weight shift, because when a tire starts spinning it likes to stay spinning,(heat build up in contact patch.

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 Post subject: Re: Let's talk 4link
 Post Posted: Sun May 28, 2006 12:42 pm 
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Ken0069 wrote:
I just bit the bullet and did the calculations on my car's 4 link setup. The way the rear frame 4link mounts were installed won't allow me to move the IC any lower than 9 inches no matter where it is in length. I've only got one setting that showed up in "Dave Morgan's sweet spot" and it's 45.5 out and 12 up? I just checked the Studebaker and it's at 39.5 out and 2 7/8 inches above ground. The Camaro is at 56 inches out and 10.9 up now, which I don't think is far enough down and is too far out. I'd like to have it around 45 inches out and 5 inches up but don't have that option.

So I guess my question is, what is an average setting for other guys on here as far as IC goes? Is anyone else running the IC out as far as my Camaro is now?

EDIT: I just went back into the program and added to more holes to the bottom of the frame mount and it will give me everything I want or could need. I guess some chassis work is in my future, hey! O:)

Still want to hear some other ppls ICs though. \:D/


ken,
i had the same problem w/my 4 link after my car was "professionally" built. the lowest i could get was 12 inches at about 60 out. what a joke.

i ended up making my own 4-link plates on a mill at work. i messed w/my 4-link program to figure out different hole combo's to get them where they were more evenly spaced out. now i have a 4-link that works.

to quote my bickle book:"a longer ic tends to hit the tires slower and for a longer period of time"

like bubstr said: it all depends on the car and setup. i like the fridge analogie! the height of the ic is directly related to your neutral line.

i feel that you should be able to make it do whatever you want it to. that's what it's there for, adjustment. i absolutly love my jerry bickel book! it has everything from timeslips to tire shake in it. it's easy to read and follow and assumes that you the reader knows nothing about anything.

just my 2 cents!

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 Post Posted: Sun May 28, 2006 2:08 pm 
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Don't forget raising and lowering ride hight changes I/C as well as center of gravity. A very usefull tool if you have the coil overs and tire clearance right to make use of it. Even dropping or raising the front changes center of gravity. Example if you raised front ride hight an inch and droped rear an inch the effect would be close to 2 inch drop in I/C. rough estimate,(actualy a little less). This can get your I/C anywhere inbetween holes. This is not something i would do on a quarter mile because any area under car is counted as frontal area slowing car in traps. But bracket racing I guess it would be ok.

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 Post Posted: Sun May 28, 2006 3:58 pm 
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OK Bubstr, what roll does anti-squat pay in this? I noticed in the puter program that it changes when IC changes. Where do we want that and or is it important enough to worry about. That isn't even mentioned in my Chassisworks manual.

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 Post Posted: Sun May 28, 2006 4:52 pm 
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Ken0069 wrote:
OK Bubstr, what roll does anti-squat pay in this? I noticed in the puter program that it changes when IC changes. Where do we want that and or is it important enough to worry about. That isn't even mentioned in my Chassisworks manual.
Yes we want some anti squat, especialy in right rear to offset the compresion from torque. this will even out the amount of weight that goes on contact patches. Everything I have ever run drag car or stock car has had some antisquat. That and weight transfer maintains down force on contact patch without lifting front end too far. The hardest part is finding the center of gravity hight. Most just guess at it and say about camshaft hight, but that can be way off. I used to have a formula to figgure it. you weigh all 4 wheels then raise rear to an angle and weigh again, then figure it like you would find the hight of a tree by useing the angle and distance from tree. Been too long since I was in school ,maybe we have a math wizzard here. You want just enough anti squat to keep rear from compressing and not enough to separate, and they don't have to be the same on both sides. It will have more on the right side from preload.

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 Post Posted: Sun May 28, 2006 5:10 pm 
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Ken0069 wrote:
OK Bubstr, what roll does anti-squat pay in this? I noticed in the puter program that it changes when IC changes. Where do we want that and or is it important enough to worry about. That isn't even mentioned in my Chassisworks manual.


Anti-squat is directly affected by IC position and C/G height. If you draw a line from the rear tire contact point up to the C/G height at the front tire, that is the neutral line or 100% anti-squat line (maybe called something else too). When your IC is on the line you are at 100% anti-squat. When your IC is below the line you have less anti-squat. Less anti-squat is for faster cars.

Baselines I've seen are: (your results may vary)
60' . . . . ET . . % Antisquat
1.44 . . 10.00 . . 100%
1.30 . . . 9.00 . . . 75%
1.15 . . . 8.00 . . . 50%
1.04 . . . 7.00 . . . 25%

Buffjhsn wrote:
to quote my bickle book:"a longer ic tends to hit the tires slower and for a longer period of time"

That is the way I understand it, seems opposite to the chassis works manual ken quoted.

Rick


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 Post Posted: Sun May 28, 2006 7:28 pm 
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here is a site I just came across...What do you guys think?..

http://www.raceglides.com.au/TechInfo.htm

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