Need advice on 4 link

Old 08-25-2007, 09:06 PM
  #1  
fallguy
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Default Need advice on 4 link

Just wanted to see if you guys could lend some input. I'm not sure if it's worth changing my preload or adding spring in right rear, but the left comes up and I'm cutting 1.24 60ft's with 1.23 as my best. It seems to track straight, but not sure if there is more in it if I get it to lift front straight. I have a 4 link setup. The car is really front heavy. My ratio is like 56% front and 44% rear.

Thanks,
Matt

http://www.youtube.com/watch?v=n6D6-DLqB_Y
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Old 08-25-2007, 11:33 PM
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edvancedengines
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My suggestion is to forget trying to make the front come up level. You have a 4 link not a ladder bar car. Ecah side of the rear suspension is operating independently to the other. It is likley the left front is coming up because the right rear is pulling up into the fender. When one corner does an action the opposite corner needs to be able to react and not be bound.

The top 4 link chassis minds do the adjusting on the 4 link on NHRA Pro Stockers. Do you ever see them launch with both front tires up the same amount? They could if it were better. They ahve double adjustable 4 links with bar adjust capanbility and even bracket up and down adjust capability. They have the best in anti-roll bars and shocks. They intentionally allow the suspension to work as it should to move the car out quicker.

You adjust rear pre-laod because a car is driving to one side during launch or first part of track acceleration. Adjusting pre-laod to get the car to rise level can be done but will bind the rear suspension movement and will also possibly cause the car to drive to the left. It will also slow you down if none of the other negatives show up.

If you have an anti-roll bar adjsut it to be neutral with driver weight in car. That is astarting place. Do not adjust anti-roll bar to make car launch level.

Ed
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Old 08-25-2007, 11:43 PM
  #3  
edvancedengines
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Surely you don't have the Mazda 2.2 in that thing?

I love it.

In a way it looked a little like you have a little too much tire plant but on the other hand it also looked like the track was not hooking hard so you may need that hard of a hit.

I did find three vids there and looked at them all. Really good looking car.

There is nothing wrong with the way that left front is coming up. looks good.

You can try gradulay adjusting extension on the rear shocks a little to make the extension to be a little stiffer. It really does look good though

Ed
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Old 08-26-2007, 05:04 AM
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BillyShope
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You most certainly do NOT want the left front to rise before the right front. You DO want them to rise equally. The goal is to have equal rear tire loading during launch and that is achieved ONLY if the weight is removed equally from the front tires.

The sum of LF and LR MUST be equal at all times. If it were not, the car would be in the process of rolling over. When the LF and RF are unloaded unequally, it means the rear tires MUST be loaded unequally and that means both a loss in performance and a decreased safety factor.

Neither a non-preloaded symmetrically adjusted 4link or a similar ladder bar can provide equal rear tire loading during launch. With preloading, equal rear tire loading can be achieved at a single value of driveshaft torque. A better solution is an asymmetric adjustment of either the 4link or ladder bar. With this arrangement, equal rear tire loading can be maintained for ANY value of driveshaft torque.

See pages 19, 4, 5, and 6 below:
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Old 08-26-2007, 02:24 PM
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Bubstr
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To me it looks like your close, if your not running an anti sway bar. Do I think your leaving some 60 ft time on the table? Yes some. A little wheel speed is a good thing, dead hooks break things and the tires have a traction window. That means they provide about the same forward force up to a point, then they give up. Tire guys call it slip angle. They call it slip angle because they figure it with circle track guy in mind, the side force and forward force is added together and when force exceeds slip angle you get smoky burn out.

In your case, your only concerned with forward force. The closer you can get too but not a dead hook the better it is. This is controlled by how much traction your tires have, how much power your delivering to the tire contact patch and how much pressure your applying to contact patch. Getting even pressure is important because tires work as a team, and a team is always better that a super star and a weak player.

Mr Shoppe's Chassis dyno is a great place to start, as most of us don't have in car suspension loading recorders. We can see the uneven front, but that can lie depending on how rigid your chassis is. A better way would be to measure compression and separation in the rear suspension. You can measure this with a couple things you have at home. a rubber band tied around shock shaft will give you compression. Push rubber band to shock body and do a launch , how far down it is will be the compression in inches. By raising your chassis to a set measurement and making a chain of wire ties can tell you separation. when the ties stop breaking you ran out of separation. miss all the bumps for accuracy, and let it roll out no breaks for separation measurement.

Most any way you cure this is in fact some kind of preload or an instantaneous preload. Static weight preloads chassis, spring adjusters preload chassis, heavier spring preloads chassis, instant center changes that are different from side to side, instantly preloads the chassis. Even an anti sway bar is instantly preloading the chassis. I really don't like the term preload, steering weight would be a better word. What you want to do is steer a little more weight to that right rear tire, and if you do your front will be level, and your tires will pull as a team.
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Old 08-26-2007, 03:12 PM
  #6  
fallguy
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Thanks for all your replies. You cannot believe how thankful I am that I stumbled onto this forum. It is a wealth of USEFUL information from guys that have real life experience in this area. I've been reading Mr. Shope's site and articles by Ed as well.

I actually built this car in my garage. I started racing the car with a 450whp Mazda 2.0 turbocharged motor that I ran 11.25 with. I then backhalved it and then stuck in a Toyota 3.0 2jz engine with GT42 turbo. Unique setup but long story. I'm using a powerglide tranny with transbrake. I launch with around 34lbs of boost and 75 shot to spool turbo. It doesn't have a anti-sway bar in it, but I've been thinking of adding one. I just didn't want to add it if it wasn't going to help in a big way. I'm using the cheap Competition Engineering 3 way shocks in the back and Tokico Illumina 5 ways in front. The front is all stock except for coilovers and shocks. I just reversed the spindles from FWD trim and added a mustang rack. I will try and run the chassis calc and see what it comes up with. I do have access to a nice set of scales.

So far when I scaled it it was this: RF 852 LF 790 RR 583 LR 564

I will try and increase spring on that corner to see if the front will come up even without sacrificing the other end.

Thanks!!
Matt

PS Ed...I like your sig!
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Old 08-26-2007, 03:44 PM
  #7  
BillyShope
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An anti-roll bar is a big help for those with a symmetric 4link adjustment, but, with an asymmetric adjustment, you don't really need it. (There are other tricks, also, such as limiting right front rebound travel.)

Bubstr's concerns are justified, but, with the traction dyno, these parameters can also be measured directly and quickly.
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Old 08-31-2007, 11:58 PM
  #8  
zipper06
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Hey billy thanks for posting your tech URL, my Malibu is so screwed up it pulls i front 1 ft. higher than the other. I bought the car as a roller and it used to have a b/blk and i put a s/blk in. It would stand on the back bumper before i put wheelie bars on it. It does come back down straight and runs straight down the track, but i think i'm leaving something on the table yet. It a back half 4 link that weighs 3250lbs with 14X32's It has run 1.41 60 ft times at Memphis, but usually 1.43/1.45. It has so much preload that if i jack the car up in front in the ctr. there's 6" differentance from one side to the other. I haven't tried to ajust it because it alway runs straight and it's pretty consistent. But over the winter i'm going to get after it since i'm going from a 377" to a 434" and now that i have your tech sheet i may be able to correct it.

Thx's again.

Zip.
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Old 09-11-2007, 10:56 AM
  #9  
davesupra
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Fallguy added some spring to the passenger rear and I think it helped a little. He cut a 1.21 and then a 1.20 60', running a 8.59 @ 158 with the 1.21 60'. The pass with the 1.20 60' had to be aborted when it got loose in the middle. The car seems to pull to the right a little right out of the hole, does that make sense after adding some spring to the right rear? Here is a vid of the 1.21 60'

http://www.youtube.com/watch?v=T4EKyOt4rNI
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