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 Post Posted: Tue Oct 19, 2010 8:05 pm 
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http://www.dragstuff.com/techarticles/P ... uning.html

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 Post Posted: Tue Oct 19, 2010 8:54 pm 
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It says this in that article---
" In fact, many high eight to mid-ten second cars will tolerate a significant amount of pitch, resulting in an instant center that is at or beneath ground level. The raked bar sets up a lower IC, and since low=long, it makes up for the high anti-squat/low ‘bite' setting of their top bar. Higher-powered cars won't tolerate all that bite- so dialing a bunch of hook will result in a tire that wads up and either spins or shakes. They demand a flatter bar, yet one that won't go over center during anti-squat. "
'

Humm ---- try that down angled lower bar (IC below ground) on your 600hp machine and it will spin the wheels, try a flat bottom bar on your 2000hp supercharger and it will sky wheelie. Thats what Ive seen happen to cars in the past. Seems what I've seen is opposite what this guy is saying.

He also says"The angle of the top bar is the final ingredient to determining how much bite the tire will have, and for how long. The flatter the top bar, the easier it is to use its pull on the chassis to plant the tire."
If the top bar is flat there is no upward force on the chassis from it. I think guy has it all backwards. If both bars are flat there is no upward force, its a parallel setup.


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 Post Posted: Tue Oct 19, 2010 10:03 pm 
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Ya know, funny thing is that at the end of the day, whatever works best on YOUR car is what is needed and all those theories and stuff that prove this or that are irrelevant in my book. When I make a change I look at the time slip and that tells me what I need to know, ie, if the short time was off then I went the wrong way. That 4 link calculator program I have is only useful to let me know where I am with that setup. I believe that sometimes there is such a thing as too much information, especially on a bracket race car.

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 Post Posted: Wed Oct 20, 2010 1:07 pm 
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I think it is very important to understand "why" it works the way it does , but there are too many "experts" out there selling software and having 4 link tech classes that want to make it look like a 'black art".

One redneck way of describing why it works you can hook a tractor to a good size log with the draw bar all the way down , take off pulling the log and raise the draw bar without changing the throttle on the tractor or lifting the log off the ground. The higher the draw bar is the more traction the tires will get and if the log is heavy enough you will pop a wheelie =;
You have not moved any weight on the tractor or the log only changed the angle you are pulling on the chain , but more important the height of the attachment point has changed .

A piston is at top dead center , you turn the crankshaft 180* and the piston is at the bottom of the cylinder , if you only turned the crank 90* the piston is past half way down the cylinder O:)


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 Post Posted: Wed Oct 20, 2010 4:40 pm 
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Dennis uses the refrigerator deal, ie, where you hit it from the side dictates how it will move. If you run into it and hit the bottom, then it will fall back on top of you. If you run at it and hit the top, then it will fall away from you but if you run and hit it directly on the center of gravity, then it just moves away while still standing straight up. The IC on your chassis is basically doing the same thing in relation to the anti-squat line.

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 Post Posted: Fri Oct 22, 2010 4:57 pm 
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Ken0069 wrote:
Ya know, funny thing is that at the end of the day, whatever works best on YOUR car is what is needed and all those theories and stuff that prove this or that are irrelevant in my book. When I make a change I look at the time slip and that tells me what I need to know, ie, if the short time was off then I went the wrong way. That 4 link calculator program I have is only useful to let me know where I am with that setup. I believe that sometimes there is such a thing as too much information, especially on a bracket race car.


We all know some of the problems I have had/having, and I am with Ken kind of on this comment. Since I have a longer wheelbase than just about all of you?beside the diggers, and I have tried two completely different train of thoughts and setup's and my initial setup worked, but it needs refinement to work really good. Also, if I want this car to reach for the sky, I am willing to bet anyone here, that it will take a higher & farther out COG and I/C setting, more higher than farther in this point. One day next year I will test this theory and report on it, someone just needs to remind me that's all =; that's a long time away :-$

My car likes an I/C just above the A/S line, and, in front of my COG! FREAKY HUH? well, it worked somewhat first time out and the chassis just floated up and out very smoothly, and now I am a believer of what works is what you go after to tune it the best you can. Remember what we all read? every car/chassis is different but we all have the same goal, get from A to B as quickly and as fast as we can per our setups. That's all I want to say about that!!! I need a better converter also. #-o

John

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 Post Posted: Fri Oct 22, 2010 5:32 pm 
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Not saying that my car couldn't be better than it is but when a 2450lb NA SBC powered door car will do 1.17 and 1.18 short times it can't be very far off. I've probably had a dozen setups in it and so far this one seems to be the best. 53.3 out, 5.0 up and 51.7% antisquat. Your mileage may vary! ;-)

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 Post Posted: Fri Oct 22, 2010 8:06 pm 
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How many deg is the bottom bar #-o
Did pit bitch ever vid the rear tire to see how it reacts?

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 Post Posted: Fri Oct 22, 2010 8:40 pm 
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Beretta wrote:
How many deg is the bottom bar #-o
Did pit bitch ever vid the rear tire to see how it reacts?


Just measured it and it's 3* +/- a half and no, he only has a cell phone camera now and hasn't done much with vid since I put these new ones on. That and the resolution on the phone camera isn't that good either. His good camera got horked up and he hasn't replaced it or tried to have it fixed. And another thing is I got tired of looking at the car leaving. ;-) It's much more fun sitting in the seat and feeling it! \:D/

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 Post Posted: Sat Oct 23, 2010 7:45 am 
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A long wheel base car has to have more "power" to initially hook than a short wheel base car. It has less to do with the ic placement and more to do with weight distribution and power in a long wheel base application.

When you have enough power to overcome the "leverage advantage" a longer wheel base car has you can tune the suspension , until you have enough power to produce traction its no different than a 100 lb guy trying trying to teeter tot on a see saw with a 400 lb guy on an equally spaced seesaw. The 100 lb guy is gong to need a little more of the seesaw on his side of the center point or he is going to be "in the air" a lot more.

All you are doing is adding or taking away forward bite with the 4 link , but you have got to have some bite to begin with for this to work and every car has a different amount built into it and that is why no 2 are going to work the same much especially adding different amounts of power into the equation.

My opinion here , but watching dirt track cars such as late models is one of the best ways to see what a 4 bar setup does with varying amounts of power , its really neat to just watch different cars and how they react to more and less throttle when they come out of the turns and approach the next. I know they got rear steer dialed in, but it all works the same.


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 Post Posted: Sat Oct 23, 2010 3:34 pm 
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What they do in Late model dirt cars would scare the Bejesus out of a drag racer.

I have always said, there is more than one way to skin a cat. Any set up I see, I try to figure out how or why it would work. I'm not a fan of far out IC's being any better than short. I believe it is only the relationship to the COG that makes a difference. Before you say why does it work, think about moving it out at a different line than your COG line. Most times the relationship changes. I really had trouble getting an understanding of how very low IC 's could work. After turning it over in my mind, what's left of it, the answer is, What transferred weight that isn't being handled by the bar is being supported by spring/shock package. This may have some advantage in higher HP cars. The advantage would be in less side wall distortion. There may be disadvantages also, like the ability of shock/spring to be consistent with different track conditions.

I have always said IC's Shocks, Springs are good, but weight distribution and COG height are the real speed secret. There is no bells and whistles to it, just some hard work, and it makes chassis tuning so much simpler. I'm big fan of KISS Keep I Simple Stupid. If a car with no suspension can get hooked, how did they do it with out the bells and whistles? Simple, they have the COG in the right spot for their power and traction. If a car with a suspension did this, The IC, Shock, and springs wouldn't have much to do. You know, some of the best preforming tools I've had are tools that didn't do much.

The point is, if spring/shock, didn't have to control, unnecessary Compression or Separation, they would be more effective tools. This works going forward or sideways.

And No I'm not selling anything LOL

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