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 Post Posted: Fri Jul 30, 2010 6:17 am 
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Billy,Correct me if this is wrong but you say that your ic line goes from the reat tire patch to the front axle cl..??

If that is a true statement my 4 link program shows it to the top of the front tire..

If this is correct then your aq % will be more than mine..right #-o

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 Post Posted: Fri Jul 30, 2010 6:26 am 
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shrinker wrote:
...the inertia from the CG is identical.

True. The inertial force generated at the center of gravity is horizontal, directed toward the rear, and of the same magnitude as the thrust force generated at the rear tire patch.

Thus, there is a horizontal force balance for the entire car.

Since the center of gravity is located above the tire patch, a moment (torque) is created which must also be balanced. With 100% antisquat, this is achieved with vertical forces at the front and rear tire patches. Like the thrust and inertial forces just described, these, too, are equal in magnitude and opposite in sense.

Thus, there is a vertical force balance (and moment balance) for the entire car.

That vertical force at the rear tire patch is the vertical component of a force vector which passes through the instant center. Now, if 500 inches of weightless wheelbase is added forward, that vertical force is still acting at the rear tire patch, but, since the front wheels are almost weightless, there is not enough vertical force available at the front for a vertical force balance.

The result is that the moment imbalance drives the rear of the car upward, reducing the force carried through the springs until, dynamically, there is again a vertical force and moment balance.

Realize, of course, that only dynamic forces are under consideration. When static forces are included, essentially all of the total weight has been on the rear wheels throughout the launch.
http://www.racetec.cc/shope


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 Post Posted: Fri Jul 30, 2010 6:32 am 
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Beretta wrote:
Billy,Correct me if this is wrong but you say that your ic line goes from the reat tire patch to the front axle cl..??

If that is a true statement my 4 link program shows it to the top of the front tire..

If this is correct then your aq % will be more than mine..right #-o

It's a line of constant percent antisquat, not an "ic" line. And, there are an infinite number of them. The one shown in the 4link programs is for a 100% antisquat line. It does not go to the top of the tire, but to a height, directly above the front tire patch, equivalent to the height of the center of gravity.
http://www.racetec.cc/shope


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 Post Posted: Fri Jul 30, 2010 6:53 am 
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Ok but you didn't answer my question...Are you using the same line in your program of the AQ line??

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 Post Posted: Fri Jul 30, 2010 7:14 am 
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Anyone who has played with the 4 link soon finds out that if you angle the bottom bar up at the front the car will climb into the air, Beretta knows what happens with the lower bar. =;
A powerful drag car or one with a high CG can be stopped from climbing or the wheelstand severity can be reduced by angling the lower bar down at the front. There is a limit to all this of course, once the car acceleration G alone is enough to lift the front wheels there is not much you can do about it other than lower it or reduce thrust etc.

What a 4 link or a ladder bar does is it increases the downward force upon the rear tires to a higher value than would be achieved at an equal acceleration rate without it.
A simple thing to do is look at a Sprintcar. The torque tube on a Sprintcar does the same thing in supplying additional downward thrust to the rear axle. It lifts the body of a Sprintcar at the torque ball point. The torque tube on a Sprintcar is a single arm version of a ladder bar, Its a simple thing to look at and understand. The tube has a slide in it so it can allow spline movement etc but that also prevents it from pushing forward, all it can do is resist torque. The diff torque reaction is upward force at the ball. Its a bit of a no brainer. Its not like trying to visualize how a 4 link works. Its a defined point of force action. If you convert a Sprintcar into an open drive line and install a set of parallel rods to hold the Diff torque the car wont pull wheelstands as easily. I know that, because I've done that.

With a 4 link the IC is similar to the torque ball on a Sprintcar, it is the same in its upward force component but it has the added force of forward direction as well. So when we talk about force vectors, we are saying that the 2 forces of upward and forward combine to create 1 single force at a given angle. In order to understand how the force vector is moving around on a 4 link you need to work out the reaction from the CG to the IC and the force vector from the IC. The IC force vector might align with the CG or not. It makes a difference where it goes and where it moves to and how fast it moves etc. That's how I work out our car.
BillyShope wrote:
but, since the front wheels are almost weightless, there is not enough vertical force available at the front for a vertical force balance.


If the front wheels are 500" forward they wont weigh much I agree BUT that weight is on a 500" arm. Have you ever gone fishing? =; hang a 1 lb fish on the end of the rod and you have to supply a lot of torque to hold it up but you only weight one pound more on the scales your standing on. Make the rod shorter and you dont have to hold as much torque to hold the fish off the ground. The Weight available on the front wheels is less, yes, but its further away so the torque is great. There's your balance.

Lets just analyze the upward force component. If you place the IC directly under the CG the upward force will lift weight off of both axle springs according to the distribution percentage on each axle. EG. if the CG is in the middle of the wheelbase then it will lift equal amounts off each axle. If the distribution is 60/40 then the amount of weight lifted will be 60/40 per axle etc. That satisfies the torque balance ( we are not accelerating here, its just a car on a dyno. ) It doesn't matter if the front wheels are 500" forward or not, if the IC is under the CG it will be an even lift. In order for a physics explanation to stand up as correct it must stand up to all combinations. So if my front wheels are 500" forward and I want to lift weight according to the distribution off of both axles then I have to place the IC directly under the CG. If the front wheels are in a normal spot and I want to do the same then I still place the IC under the CG. That means that the upward lift effect of the IC is related to the CG not the Front axle position.


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 Post Posted: Fri Jul 30, 2010 7:15 am 
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Beretta wrote:
Ok but you didn't answer my question...Are you using the same line in your program of the AQ line??

Sorry. Didn't catch the question. Yes, that is the 100% line in my program. Watch out for those programs which show a line from the tire patch to the center of gravity!!
http://www.racetec.cc/shope


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 Post Posted: Fri Jul 30, 2010 10:08 am 
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shrinker wrote:
If you place the IC directly under the CG the upward force will lift weight off of both axle springs according to the distribution percentage on each axle.

No, that's not how it works. The instant center can be located at any one of the infinite number of points which make up the line of constant percent antisquat and the result remains the same. This is because the force vector acts along that line. It hasn't the foggiest idea whether the instant center is below the center of gravity or not. That's why there's an infinite number of valid points.
http://www.racetec.cc/shope


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 Post Posted: Fri Jul 30, 2010 10:54 am 
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Hello Billy, We are separating the forces into their respective upward and forward components for this exercise.
If I extend the length of the four link bars so that they meet at one point that point is the IC and the force vector will be applied at that point. If i make that point under the CG then it will do what my previous post said. If i extend the bars all the way to near the front of the car the force vector will occur at that point. It cant occur anywhere else, It has to be there because I put the bars to there, so the lift component will lift it from there. I know and you know,that there is a force vector and that force vector moves position and angle due to 4 link geometry, but you keep saying that the location of the front axle changes the necessary 4 link geometry to achieve 100%. I'm saying the thing that determines the motion of the 4 link is the CG and what you do to it. Its how hard you accelerate the CG and create inertia at the CG that determines what happens in the 4 link. That's what results in a downward force sent through the link bars to the rear tires. The CG is the inertia point of the car, it doesnt matter where the front wheels are. It matters where the CG is. You could chop the whole front end off the car and only have a CG and a rear end and it will perform the same.


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 Post Posted: Fri Jul 30, 2010 12:38 pm 
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Shrinker, I know I said I would back out of this =; , but when you start lengthening your link bars you add leverage as far as the upward lift of the link bar. It gives less weight an advantage over the housing in your hypothetical example. No different than fetching a longer breaker bar out of the tool box to turn a bolt torqued to a certain amount except exactly backwards from where the work is coming from .


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 Post Posted: Fri Jul 30, 2010 2:23 pm 
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shrinker wrote:
If i make that point under the CG then it will do what my previous post said.

No, that's simply not gonna happen.

Perhaps what you're missing is that a force can be placed anywhere along its line of action without changing the effect. For instance, you can balance a pencil on your finger or you can tie a string around the balance point of the pencil and support the pencil from above. Same force. Same line of action. Different points of force application.

The force acting on a line of action which passes through the rear tire patch and the instant center can be considered to act at any one of the infinite number of points which constitutes the line. So, the vertical and horizontal components of that force can be applied anywhere along that line without effecting a change.
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 Post Posted: Fri Jul 30, 2010 2:42 pm 
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ky mustang wrote:
Shrinker, I know I said I would back out of this =; , but when you start lengthening your link bars you add leverage as far as the upward lift of the link bar. It gives less weight an advantage over the housing in your hypothetical example. No different than fetching a longer breaker bar out of the tool box to turn a bolt torqued to a certain amount except exactly backwards from where the work is coming from .




KY, I remember your stang after the new motor on it's first pass your nearly broke the wheelie bars in half...So tell me where you 4-link was set and where you moved it to now as I just seen your vid and it looks good..Barely any separation at all...

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 Post Posted: Fri Jul 30, 2010 4:02 pm 
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Beretta wrote:
KY, I remember your stang after the new motor on it's first pass your nearly broke the wheelie bars in half...So tell me where you 4-link was set and where you moved it to now as I just seen your vid and it looks good..Barely any separation at all...


When it bent the wheelie bar brackets the change I made was going from 4:30 gears to 4:86. It had never been on the bars hard at all with the 4:30 gears even though it had a 60' of 1.09 so yes it was a surprise to say the least =; . The ic then was around 56" out and 6.5 high if I remember correctly. I have not measured it since I moved it just watched the separation on video frame by frame.

I moved the front bar up one hole in the front and raised the ride height a little to bring my bottom bar to 2.5 *. I will measure it for you soon and let you know where it is. The car is working so well there and everyone that has watched it says don't touch it .

The guys I run with in the dixie door slammers are running either blowers or nos I am naturally aspirated . The only car that will 60' with my car is Duck Dyson he is running a 706 cid on nitrous jerry haas chassis . The best 60 he has had that I know of this year is 1.06 and mine went 1.05. They can out et me but they can not out 60' me =;

I am not bragging on my car , I am very very happy with it don't get me wrong , but it should not be producing 60' times like that , its just a 562 with conventional layout heads. There is an engine 557 built kinda in reverse of mine 4.500 stroke x 4.44 bore same heads that belongs to a friend of mine. It made 943 HP mine made 951 hp. His is on a dragster that is 400lbs lighter than my car and it best 60' 1.02. We have ran on the same tracks so its not discrepancy with track timers.

What I am getting at is the car has to be very efficient to do that and it is not bound in place by stiff shocks stopping the separation or squatting , it has to be a result of the a/s % and the cog placement matching my power level.

What Billy and Bubster had explained to me started to sink in when I was helping a friend on his 4 link. It was supposed to be set at 100% , he had a cardboard drawing of his brackets and I saw and compared his settings my self. I watched this setting on video the car squatted more than mine did and mine was set to squat at that time. So i said the only error can be that we were guessing at the cog height being at the cam shaft. We reset his car just by a huntch and surprise it did not squat or separate and ran the best it had.

He did not want to set it there because the ic was shorter and higher than everybody else had suggested , but the car ran 5.80's there. He has since moved it out longer and lower( "to be where it should be") and its running high 5.90's-6.00's now.


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 Post Posted: Fri Jul 30, 2010 5:09 pm 
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ky,
You mentioned your buddy's COG and he used the camshaft, or whoever set the car up,, well, I am kind of using my camshaft also as my COG height as well since I don't have scales. From what your saying, if the COG is not where you think it is, is there another way to find it besides raising the back of a chassis up and using scales? I have not red anywhere that it can be done any other way. I am just wondering if my COG height is not really the cam heigth! maybe higher, maybe lower :-k

I would think that the center of gravity, power available, and where the I/S is placed is the key to all this, so if one has a miscalculated COG, then he could be searching for a while to find the optimum spot for the setup right?

And, from what I am reading in all these posts is, everything revolves around the COG period, and it is the balance of power, 4 link location and where it is in relation to the neutral line that the balance needs to be perfect to have the best setup per any given vehicle, correct?, or finding the best leverage spot?

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 Post Posted: Fri Jul 30, 2010 5:43 pm 
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What I have done is just trial and error so to speak. I have basically just found a spot to where the shocks have very little effect on the separation / squatting of my chassis.

The chassis basically is just leaving efficiently with very little chassis movement It is by no means mathematically proven like the instructions in the thread at the top to be at exactly 100% a/s. It is acting like it is or is close though. I do not have my own scales , but I do have access to some and probably will go through the steps to see just to satisfy my curiosity.

Quote:
And, from what I am reading in all these posts is, everything revolves around the COG period, and it is the balance of power, 4 link location and where it is in relation to the neutral line that the balance needs to be perfect to have the best setup per any given vehicle, correct?, or finding the best leverage spot?


Yes, but remember that you may have to move weight ie the engine forward or backward up or down , battery , etc to change the cog to work correctly with your wheel base, and power level.

Being able to run the a/s at 100 % is for the many reasons Billy and Bubster have mentioned , and all of your power is used for going forward and not absorbed by your suspension , or a wheel stand. It is not what makes the car work 100 % correctly.

A set up that is not at 100 % will work , just not as efficiently and you use the shocks to band aid the a/s set up that makes the car work , nothing wrong with this that's what they are for , but you are leaving some et on the table.

Its also possible that the cog can be so far off all you will have is a wheel stander or a spinning car.


That's the way I take it ,
Billy or Bubster feel free to correct me if I am looking at it wrong.


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 Post Posted: Fri Jul 30, 2010 6:15 pm 
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Step back and look at the believe that your links pr IC point is lifting a car. The rotational torque of the rear has a force, but nothing compared to the instant forward motion of the car. To say the link is raising the car is like slapping a cannon ball coming out to speed it up. The car is transferring weight from forward motion, not links, or you wouldn't be able to set them low enough to get a squat in the rear.

As everyone knows, there are always more than one way to skin the cat. We will see about every way possible on chassis set up. A lot of them work. A lot of them don't work for everyone.Why they don't work is the fact that no two cars are the same. I once had a car with more than 100% anti squat. It was so bad it hopped like a bunny. I put garage type door springs on it. Two heavy ones on each side. That settled it down. That wasn't the best fix and wouldn't recommend it to anyone. Not knowing any better at the time, I thought I was right, But as you can see, we end up compensating for anti squat with springs and shocks.

If your really running under 100% anti squat and getting no compression, you have to make it up by carrying weight on springs and shocks. This works but taxes them more. A little of it can even be good on a rough bumpy track.

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