This is from Ed from Advanced Engines on Yellow Bullit, He was a great racer , Rngine builder an Chassis guy, he passed away not long ago but I hope I have saved some of his best advice for us.
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If you do not agree with this it is ok. This is only the ideas theories and opinions of one man. This is a little Mini-Seminar based on my personal experiences.
This was originally written and posted in parts on a Tech Page that I wrote for a Racing Forum on the internet. I wrote this as several separate postings, initially to just be answering some questions.
I have made a few addendums to this since I originally wrote it.
Hope this is of some help for you. If any of you are helped I would love to have you send me info about it as a form of appreciation.
Ed
Introduction to 4 link suspension basics & Theory.
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Introduction to theory and descriptions.
Part 1
My first and very real suggestion to you, and to all racers is to buy some books on basic race car chassis design and adjustments.
I will post three of the links to sources which may be helpful for you to purchase. You will discover that if you research and read writings by different authors and builders, that they all do not use the same theories or the same terminology.
This can get confusing if you do not understand that some of the different terms are describing exactly the same thing.
Examples are;
Tire or chassis Separation = Anti-Squat = Tire Hit.
Negative separation = Squat = Not enough tire hit.
Many years ago Alston Engineering, Chris Alston, developed his own theories and his ways of explaining. He also sold many chassis training tapes and also conducted chassis schools all over the country and the students came out with words and theories and descriptions which were different than what the other chassis men like Don Ness, Willie Reils, Don Hardy, Gateway, were using.
Those guys, used the same terminoligies that Most of the older guys like me were used to, so we were all talking on the same page. We all could actually talk and discuss suspension tech on the phone and the other person knew what each other was meaning.
Now there is so many different ways to explain theories that I too get lost in their explanations. I have still never seen any benefit to using the Percentage of Rise theory. Yes it does work once you can figure what is your theoretical Percentage of Rise. None of the theories take into consideration the individual ar's power differences or gearing differences etc. So to me it is all fictional or loose theories of what is an actual "Squat/No Squat/Anti Squat Line". No matter what ficticious percentages you call it the bottom line is you are still moving your Instant Center, up or down or forward or backward, just like we have been doing for ages.
Now some of the chassis builders are using the words originally started by Chris Alston and later picked up by Dave Morgan and others. He uses a theory called "Percentage of Rise" and the words of Anti-Squat". Anti-Squat is easy to understand. "Percentage of rise is not so easy". You can make either theory to work and to work right but I am more familiar with just using the Imaginary line of theoretical Instant Center (similar to Chris Alston's Neutral Line. The Neutral line is the Squat/Anti Squat/No Squat Line) than I am with using the Percentage of Rise, to explain things. I also can add that as big as Alston Engineering is that they have never had a Pro Stock car using their designs to ever be a winner or champion. One time many, many years ago, they had a ladder bar car that they themselves ran that did win one Pro Stock race. However they did also do some great work on
Dave Riolo’s car when it was first re-done years back and it worked very good. So you can do whatever you wish with that
piece of worthless info. .
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Tim McAmis chassis plotting software.
"Chassis Master"
<http://store.trackerdesigns.com/Mer...tore_Code=TMRCI>
http://store.trackerdesigns.com/Mer...tore_Code=TMRCI======================================
Jerry Bickel Chassis plotting software.
"4 LInk Wizard"
Plus get and read this treasure book;
Complete Guide to Chassis Performance Manual
"The Chilton Manual Of Drag Racing"
<http://www.jerrybickel.com/software.html>
http://www.jerrybickel.com/software.html======================================
Dave Morgan
BOOK: Doorslammers: The Chassis Book
Doorslammers Chassis Tuning Package
(some good info here and some bad info too)
<http://speedtalk.com/doorslammers_drag_chassis.html>
http://speedtalk.com/doorslammers_drag_chassis.html======================================
It is very beneficial for you to know or to learn just what happens when you adjust or locate any component of your rear suspension by using basic laws of physics. Also know and remember that with a 4 link that all suspension angles, measurements and adjustments rapidly or instantly change the moment you begin the launch applying forces of torque. Then it is almost as if the right and the left are seeing different adjustments because of the change in bar angles as the right rear tries to lift inside the right fender.
Anti-Roll bars do help a lot but they are another integeral part of the entire rear suspension equation that needs to work in a balanced force with all other components of that rear suspension. Each piece is as critical as any other piece. Always remember that Anti-Roll Bars were not intended for adjusting Pre-Load. They are not named Pre-Load Bars, They are named Anti-Roll Bars, but with a few factory suspension cars like the Chevelle, Malibu, Cutlass etc and Mustangs the Anti-Roll bars can help when spring adjustments are not enough, and any bar adjusting would upset the rear alignment. On all other cars it is my opinion that they should always be adjusted to be neutral. I do not believe that Anti-Roll bars can be any benefit with a correctly set up and adjusted Ladder Bar car. I know there are many who disagree. There is no stronger torsion bar than a rear end housing if it it welded and is braced.
The other theory which is more commonly used is more simple in description and establishes a theoretical ideal "Point of Instant
Center" that uses an imaginary line from the rear tire contact point center that will be diagonal to the actual point of the car's real
center of gravity. The Percentage of rise theory moves down below the actual center of gravity and then draws their imaginary
line to the tire contact point. For this article I completely will do away with Percentage of rise except just to talk against or to
compare to it.
Percentage of Rise (PR)
Anti-Squat (AS)
Neutral line (NL)
These are all words phrased in Chris Alston's Chassis Classes years ago and are now used by some shops that were trained in using them to describe what was taking place in suspension settings.
Know and understand that anytime torque is applied that your left rear tire will be trying to push down and your right rear tire will be trying to rise looking from the rear of car. All cars in any kind of racing or activity will exhibit this twisting motion if there is any form of friction coeffiecient existing between the tire rolling surface and the ground/track/road. The tendency will still be there to twist the rear with torque even with no tires or wheels. It is when you start to hook that it really shows up.
If your rear end was not attached with brackets, when the driveshaft rotates in the counter-clockwise movement (looking from rear of car), the entire rear end assembly would rotate counter-clockwise like a propeller if it were suspended in the air and had rooom to move. The driveshaft rotates in the direction that engine torque is applied to it. Even attached with bars and suspension it still wants to rotate.
Always keep in mind that As greater torque is applied the rotational force will be greater so as power increases
the car will want to pull to the right, which we counterct by suspension preloading in adjustments. If doing any bar preloading do know that even only 1/2 turn is an extreme adjustment from neutral load position. We usually preload bars in increments of portions of a nut flat when we are close. 1/2 of a flat can make a car go straight that was trying to veer to the right. Too much bar preload will pull us to the left and quickly can get us into the wall.
Corner weights are set or adjusted in several different ways.
Physically moving weight
adjusting weight preload with springs or spring adjustments
adjusting preload with 4 link or ladder bars
adjusting preload with an anti-roll bar (not prefered).
A lot of times what is considered to be an ideal weight bias on the corners with car sitting in a shop is not close to ideal weight bias during launch and going down the track.
Funny thing about weight bias and preload;
What can make a straight launch can also cause some down track problems and unequal unloading while stopping. There has to be a balance of what launches good, drives good, and stops straight.
To further complicate it all is that the more power you launch with the more the car will drive to the right, so we add preload into the right rear and the left front to act as a counter force.
To make it even more tricky is that if you have a car just right to launch good and stop and drive good, and you lose power or reduce tuneup etc, then the car will drive to the left.
The higher the horsepower is, the more tricky it all gets.
How many of you noticed that when Jeff Naiser was sorting his car out and running in the middle of the pack and at times not qualifying, that then his car was always driving initially to the left and would then get straight further down track. BUT when he was finally able to get his full power to the track and ran his string of low 4.50's and 4.40's that his car launched and ran and drove arrow straight. You see, his car was set up to run the number. When he was off on power it drove left. How could they have known what preload would work best when the car was able to do full power? Several reasons. Good educated guessing with much 4 link experience with that same car and lower powered engine. The first few times out the car ran and hooked pretty good and gave then indications of what to expect with it. Robert Fulmer is a very good suspension man.
I personally prefer a 4 link set up to anything, IF I am the one doing the tuning and adjusting. If not I usually do a different suspension set-up so customers can make simple changes. Ladder bars are very simple and are easy to teach a customer how to adjust and when to adjust them.
Truth is there are many racers using 4 link that really have not a lot of understanding of physics and why to adjust what. I have seen racers adjust bars up and down going far too radical of a change pretty much with all adjustments. After I saw a question and answers to those questions in a Forum between two different owners of Pro Mod cars that were professionally built and I saw that the answer given could cause a serious crash is when I began writing this.
Most of the time minute adjusting can make huge differences. Simply a small change in rear ride height will alter the bar angles and the active point (Actual) of instant center. Slightly moving the front of the bottom bar and top bar down (lowering actual instant center, and at same time not moving it forward) can at times make a big difference in a car that tries to lift the left rear of the car like in a barrel roll, and also can help to keep the front tires from lifting as quick. This applies to cars with equal length bars. This quickee rule of thumb does not apply equally to cars with two different length bars. The effect will be similar but the Instant Center will also move rearward at the same time.
Contrary to what many of your chassis shops will set and their adjustments, what you really want is in most instances the bottom bar will be near to level while under hard torque and full acceleration, not when the car is sitting still with no torque applied. Sitting still it will likely have the front of bottom bar lower than the rear of the same bar, by just a few degrees.
If the bottom bar is close to level before the launch and the left front side of car is rising and the tire is planting lifting the rear, there can be a very negative effect called "Barrel Roll". That is because with all the suspension movements the bottom bar on the left can end up pushing upward and the bottom bar on the right side is pushing downward. Opps. Can you say Whoopie!. Animal Jim's car was a good example of this, also Charlie Bucks, car was too. I also had one that did that until I changed the bottom bar. Simply lowering the actual point of instant center which would also place the bottom bar in a downward angle can eliminate this.
Anti-Roll bars now also help this. If lowering Instant Center is the only desire in change while keeping actual distance of Instant Center the same, you must move both bottom and top bars the same amount in the same direction. You can also move the rear of both bars up one hole if it looks close to the same IC length when you plot it out on paper, computer or however you plot out your suspension positions. There are now computer programs that can help you quite a lot as I mentioned earlier in this thread.
If you will look under any top 16 Pro Stock car you can notice that the bars usually have not been in more then two to three different holes even from the very beginning. Most of the adjusting between the holes comes with the initial baselining while the car is new. Once a good overall baseline is found, most other tuning and adjusting to differing track conditions is minimal. Even slight adjusting changes make a big difference.
I feel that good quality Double Adjustable shock absorbers are one of the most valuable suspension tuning aids there is and is money well spent. Cars running quicker than a 9.00 in the 1/4 really need them.
The Chassis design software by Bickel Race cars should help you to understand better and to see on your computer what can change and the reaction when even small changes are made in bar adjustments.
I can not tell you in a forum how to adjust the suspension of your particular car. No one can.
This will end the introduction to 4 link basics. Next is instructions.
Cont --> to Part 2
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4 Link suspension basics
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Cont from Part1
Part2
IN part of this section, I shall try to teach you how to determain what your actual front to rear weight distribution is by using stuff you already have, without having to go pay a chassis shop to scale your car if you are on a tight budget or there are no scales near you. Of course you are better off to scale the car but we have not always had individual wheel scales in drag racing so here is an old fashioned method that has worked for years in some of the baddest cars there was.
with 4 wheel scales it is easier to find the center of gravity and center of balance. You take the instructions I gave and use them in reverse to find where it is from the front to the rear. So if you know the total weight and the weight on each end then you will be able to calculate the percentages on each end with that info. Then you just use your wheelbase and figure for example 45 % of weight on the rear translates to 45 % of your wheel base from the rear would be the center of the car so that should be the balance point.
Write all of this info down so you will keep it in a log. Any adjustment changes you will write down and the results of them always.
1st
where is your actual center of gravity of the car.
2nd
What is your actual wheelbase
3rd
what is your rear tire diameter
4th
Place a weight in the driver's seat equal to the weight of driver. Load fuel tank, water resorvour and make the car balance the same as it would be weighted while at the starting line.
5th
get two jackstands. (I actually even place short angles on them so there is an actual point instead of the larger top of jackstand).
Now you will think I am nuts.
You are going to balance the entire car on only two jackstands, one on each side. do not give up. The car will perfectly balance. Mark that place with a piece of thin "3M FinishLine Tape" (Buy at Paint and body supply) attached to each side of your car in a level verticle line. That is the point of front to rear balance of your car. Good to write this down by measuring from balance point to the center of both front and center of rear wheel hub.
5a
Make a mark where a level vertical line is at the center of balance, to the ground or floor. Mark a level vertical line where the rear housing center is. Mark a level vertical line where the front hub center is. All of these three vertical lines will be used to determine your actual front/rear weight distribution.
5b
Measure your exact wheel base from center of rear housing marked vertical line to center of front hub marked vertical line. Write it down.
5c
Divide the distance measured horizontally level on the ground/floor from the rear housing center to the vertical level line that is at the car's point of balance by the measured wheelbase. That will = your rear weight percentage or percentage of weight on the rear wheels. Write it down.
5d
Divide the distance measured horizontally level on the ground/floor from the center of front hub to the marked vertical line at car balance point by the measured wheelbase. That will = your front weight percentage or percent of weight on front wheels. Write it down.
6th
Lower car to the ground and bounce it a few times to get it to be at normal ride height.
7th
measure from ground level to center of camshaft. That should be close to the height of center of gravity. Write this measurement down.
8th
At the exact place previously established as the car's balance point, at the height of the center of camshaft, will be your
theoritical point of center of gravity of your car. mark that spot on the door or fender by crossing two thin pieces of tape in an
X. Take a picture of side of car with tape on it.
9th
Measure all the discovered dimensions, including the measurements from front axle and rear axle to that place where the car
perfectly balanced. Write all this down in a notebook to keep.
10th
With someone helping stretch the thin tape from the place you determined was the center of gravity of your car, in a downward angle to the bottom and center of where your rear tire is contacting the pavement. This will be the Theoretical Instant Center line (Neutral Line). You will keep this imaginary line in your mind forever once you begin using it. It is only a point of reference for you. Take a pic of tape positions on car from the side.
11th
Take a picture of the side of your car with the tape showing the angular line from the bottom of rear tire to the place marked to show cam height at the balance point that we are calling the car's center of gravity.
12th
That imaginary line is to be used as a reference as theoretical "Line of Instant Center". Some call it "Neutral Line". The actual (or active) point of instant center is the actual point where a straight line extended from your top bar and your bottom bar will intersect in an imaginary line looking like a triangle shaped like a Ladder Bar.
As you move your actual instant center further forward or below that Theoretical "Line of Instant Center" (Neutal Line) (It is an imaginary
angled line, where you had your tape) The rear suspension hit will decrease, but the front will have a tendency to rise on it's suspension. Likewise, If you move your actual "Instant Center" back or up toward the Theoretical "Line of Instant Center", the rear suspension hit will increase.
As you move your actual or active Instant Center point forward of the Imaginary line of Instant Center (Neutral Line) you will promote more front suspension lift and less rear tire hit.
As you move the actual or active Instant Center to the rearward you will give it more tire hit and greater rear suspension reaction and less front suspension lift.
As you adjust for increased rear tire hit, you will be at the same time be adjusting from less effect of actual bar lift in the front.
When you adjust for decreased rear tire hit, you will at the same time be adjusting for more effect of actual bar lift in the front.
If you reach the Ideal, as the tires hook the car will rotate on the rear axle and will also try to lift the front as the car is moving forward.
ADDED 1-27-2007
Use the 3M Finishline tape which you will find at auto paint and body supply houses or paint stores. If you use a magic marker, or pen or pencil to mark on your car you will have a nightmare removing the marks. Finishline tape will stick on and will easily peel off.
Place the 3M Finishline tape in a vertical level line on the car at that point of balance. Which is easier when you have scales to weigh the ends with. At the camshaft ht place a piece of the 3M Finishline tape in a horizontal line at camshafy ht. That X where the two pieces of tape cross should be your Center of Gravity of the car. That is Center of Gravity. That is not where you want your Instant Center. I use Center of Gravity as my reference point for pretty much everything related to suspension adjustments.
Hopefully you will know that a low torque engine will be needing more adjusted Hook or Tire plant than will a high torque BB car. As the power level at launch increase you will need less and less adjusted hook in your suspensions. Sounds strange but that is the way it is.
That simple explanation is and can be misleading. Best example is the old Chevy factory 4 link. According to suspension theory that car should be very wheelstand prone, because the point of actual instant center is far forward in front of the car and is also below the Theoretical Line of Instant center. Problem is it is so far to the extreme forward that only a tremendous amount of power with huge tires to hook could possibly get it up. That car's factory tendency is to actually lift the rear tires under hard accelleration is the reason it squats. Only changing the upper bar angle to a lower front position, or moving the front of bottom bar up or the rear of bottom bar down, will give major rear tire hit on that car. Now you could also make a way to change the forward and/or rear lower bar mounting position and in essence end up with a factory but modified adjustable 4 link. lol. Rear shock dampening control is needed after making any extreme bar angle changes o that style of suspension.
There is so much more to say but there is just not enough room in a forum to get much deeper than i have.
In the older days we used to draw out all the dimensions I just discussed on a shop wall or on a shop floor to plot out the different bar angles. Now you can use computer programs. I do still do it to scale on a piece of paper though when no computer is present. Actually by now it is pretty much in my head of what to do based on results observed by Video Camera seen in slow single frame advance or with data provided on shock travel. In really extreme bad conditions watching the car can tell some what it needs, but be aware that things are happening quicker than your eye can see. Best is a video shot at an angle covering whole car from left rear corner.
Please try to learn as much as you can about this subject if you are tuning your own 4 link. It can get dangerous if you go too extreme. Also remeber also that after your run the 4 link adjustment and rear components are also important. You do not want severe rear suspension unload when you back off it either. When you cross the traps you do not want to hit the brakes and experience severe rear suspension unload or if you pull a chute. We may later get into using the actual car's center of gravity calculated at speed to determine where to place the chute tether atachment point.
One other point to make. If you set your preload with a top bar do not get wild and crazy. Before you set preload with all weight in the car you should be able to easily slide the front bolt out after removing the nut. One top bar will be used to set and adjust pinion angle. The other will be used to adjust preload to preload the left front/right rear weight bias. With this adjustment a little can make a big difference.
If you are using the top right bar to adjust pinion angle, the top left bar will be your pre-load bar. In this example you will
lengthen the top left pre-load bar to pre-load weight to the left front and right rear tires. Be careful just a 1/2 turn of pre-load makes a huge difference. Usually even a fraction of a nut flat can be noticed in your handling.
If you are using the top left bar to set pinion angle, then the top right bar will be your pre-load bar. To jack weight in
pre-loading using the top right bar you will make it shorter. Again just 1/2 turn is a huge difference.
Bottom bar length adjustments are used only to center the rear in alignment with the chassis
One last point for this post;
The rear and the front springs should be no stronger/heavier than what is needed to support the weight of the car while sitting at starting line. With strong and fast cars rear double adjustable shocks are a must.
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With any rear suspension setup, changing the ride height does change the way the car reacts.
Fortunately now there are several computer programs to aid in plotting 4 link adjustments, and those who are using them are getting good results if they can just understand the program and how they work. That is the easist way for a novice.
long or short bars. Longer in my opinion is better, But years ago Larry Kopp running out of Wayne County Speed Shop showed up with an Oldsmobile Firenza with a different cutting edge range of ideas all on the same car. He had 4 link bars that were quite a bit longer than the normal 20 - 22 inch bars, and the car did not work very well. I do not think it was because of bar length. I think it was that the complete over all set up was so radical that other parts of his suspension were working against him. They ran that car only one year. I have so many photos of that car. I do think several of the ideas on that car were really good but bottom line is it could qualify but could not win. They went to a more conventional car the next year and began winning again. Amongst everything else they had the rear coilovers operating in a configuration like a rocker arm like a Can Am car .
NOTE:
The lower the Instant Center is the less effect it has on rear suspension torque reaction. The higher it is, the greater effect it has. By theory the further forward the Instant Center is the more the front will lift and the further back the less it will lift. As I said that is just theory that in extremes just doesn't work. Weight Tranfer does still work by the front rising but in most cars today we do not want the front to rise on it's suspension any more than it is necessary. I promise you that when the front tires are off the track you have all the weight transfer you can handle. Spend more time on making the rear to work right. Once you have that you can do some extra fine tuining on the front if you need it. Most True 10.5 cars and Radial Tire cars do need some lift of the front for weight transfer. Biger tire cars don't.
Ed
I have just mentioned some of the beginning basics here. Hope I helped some.
Did that answer some your questions or did I get too far off the topic?
Ed
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4 Link suspension basics.
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Part3
ONe thing I forgot to suggest to you.
When you do get a good suspension baseline on your car I imagine that the point of actual instant center will be either right above the ground, or it could even be buried several inches into the ground and behind your rear engine plate, probably somewhere around the rear of the door and near the ground or between the ground and your frame height. Time will tell.
The measurements I told you to write down about from the point of balance to the rear axle and to the front axle you can use to figure what percentage of your wheel base is forward of the point of balance and what percentage is to the rear of it. Once you know these two percentages and you know the vehicle weight you will then know the actual percentage of weight on the rear and on the front and the amount of weight on each end of your car.
By experience I can tell yopu that 55 % on the rear is not a good idea. lol. Not unless you want a 140 mph wheelstand when you change gears. . My opinion is 47 % to 50 % is much easier to tame. I know guys with serious Outlaw cars that are placing ballast forward to even bring theirs to 46 %, trying to keep the front down some. What is right for your car is what you find that works.
Soon I will tell you how you can altar your front/rear weight distribution by the way you install your shocks. Don't be surprised if some of this sounds different. lol. Maybe we will get even deeper into this if you all wish for us to do it?
Ed
Do understand that I am not a Chassis Man and only work with chassis of my customers that are local. For years I did my own too. My experiences came as a racer in what was at one time considered to be a high horsepower car. I did go through an Alston Chasis Clinic years ago, but was mostly in disagreemnet with them the whole class. <IMG border=0 width=32 height=32>
I had a car that was a handful at the time and It did not take me real long to learn the things to not do. <IMG border=0 width=32 height=32>. I also was blessed to have at that time in my life some friends in Warren Johnson and Larry Olsen that helped me along quite a lot. That car had a tendency to pic the front end up when I shifted to high gear at arround 140 to 144 mph. Although not real high, I can promise you that loosing sight of the track at 140 mph plus is just not a fun type of entertainment. BIG PROBLEM with it was the torque and power was violent even just on motor and the rear to front weight distribution was assanine and set up too much to the rear by my ignorance. I had 55 % on rear tires when that car wanted 48%. It was very wheel stand prone and initially also wanted to do a barrel roll like those of Charlie Buck and Animal Jim.
The theories or fact I have written came from a lot of doing it wrong and learning what was needed instead. I learned what to adjust and the effects of the adjustments to get the barrel roll out. That was before there was any Anti-Roll Bars.
<I>I learned to quickly by busting a new high dollar Mark Wiliams Aluminum Raer about what Dead Hook with too much traction can do with high horsepower. I learned by experience how to not do a 4 wheel wheelstand. lol. That was not fun either becuase it too cost me a lot of money for repairs. I also learned that there is more than one way to do a 4 wheel wheelstand too. I also learned the thrill of a 3 wheel wheel stand. Not good when that other rear tire catches traction again. Can you say INSTANT TURN. <IMG border=0 width=32 height=32></I>
I have not driven a race car in years but now and for several years my learning curve has improved by working out bugs with customer cars.
Something that seems strange but is fact. It takes less rear suspension reaction with a high horsepower car than it does with a lower powered car. So for example if your car is launching perfect with a lower powered engine. When you put the big power to it the car will want to over react and you will need to tone down the rear suspension action by bar adjustments to take hook out or by shock tightening or by maybe even both. It sounds odd on the face that a lower powered car will work better with more radical suspension adjustments but that is the way it is becuase the higher powered car is transfering a ton more of torque into the suspension and tires with not a lot of reaction.
Another pet peeve of mine is cars that slam down hard on wheelie bars. If the suspension is right the wheelie bars will ride along as a safety item and will barely touch down if at all. Do not try to control your wheelstands with lowering the wheelie bars. Adjust hook out. I do like wheelie bars and am against the race rules that do not allow them but it is for safetty reasons in a just in case situation.
I ran my mouth enough today.
Ed
The dangers of internet suspension advice.
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This just came up on another board and I was freaking. Well intentioned people were trying to give someone 4 link advice by telling them which exact holes in the brackets to move the bottom and the top bars to for adjustments. The advice was ranging from, put the top bar in the 4th hole down and move the bottom bar in the end hole. and several other well meaning but very dangerous pieces of advice.
Not all 4 link bars or brackets are made or mounted the same. Some bar rod ends and bracket holes are 3/4, some are 5/8 and some are even 1/2 inches. All bolt spacing between the holes in the brackets are not the same. All rear brackets are not the same. All bar lengths are not the same. Some bars have shorter top and longer bottom bars. No one can give exact advice to adjust blindly by their knowledge or by guessing.
Radical wrong adjustments in a 4 link car with high horsepower can literally kill you.
Ed
Now here was my reply and I hope I made no one mad there.
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Subject: No one can tell you how to adjust your 4 link on a forum
Author:
A_M
[Edit] Date Posted: 13:31:40 12/06/05 Tue
Except posibly the one who is familiar with your individual set up and they know the car and where everything is mounted and aligned.
I could look at a video tape of your car up close, frame by frame, launching and be able to give advice about how or where in relation to the place everything is now mounted and adjusted, but there is no way that I or anyone can tell you which hole in your setup can work or which bar or which end needs to be adjusted.
I can suggest moving your point of active instant center forward, backward, up or down. I can suggest even shock adjustments by viewing a video tape but i will clearly state, I nor anyone can tell you which hole position will accomplich anything by guessing and on the internet.
Sorry if anyone gets angry with me about this but messing with 4 link in the dark without knowledge of all facts is one of the most dangerous things than can be done to a high powered race car. The wrong move too radical by mistake or following mistaken advice can
kill you.
A_M
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Subject: 4 Links an how they work 
February 6th 2010, 6:23 pm