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4 Link Basics. Theory & Help Instructions

Old 06-05-2008, 01:20 AM
  #11  
edvancedengines
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Someone asked about rear bar mounting positions and if it is important. on another board.

Yes it is but in my opinion at times some people make too big a fuss over bar spread in it's priority of importance.

A correct set of rear 4 link brackets will measure shorter from axle center from top bracket holes and longer on bottom for bottom bracket holes.

This is because of mechanical reaction time of top vs bottom and because of mechanical force or leverage of top vs bottom which is a multiplying factor of how much torque gets appied to either bottom or top bars.

A correct rear 4 link top bracket will also have holes for adjusting Starting at bottom hole forward of vertical axle center and each additional hole will be farther from horizontal and verticle center of axle housing. Meanwhile at the bottom the bottom bracket will have all adjusting holes to be in a straight vertical lineeither at vertical center, but usually slightly forward of vertical center.

The longer leverage at bottom will react quicker but not as much immediate force. The shorter leverage at top will react slower but with much greater instant force.

So yes' It is important.
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Old 06-05-2008, 01:23 AM
  #12  
edvancedengines
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If you must use the factory stock suspension components;

Ditch the 90/10 's. If it still has a front anti-sway bar remove it. If you need front lift, remove control arms and measure length of bushing with teeth. Grind teeth off of bushings. Hone inside of bushings so the bolt is a light slip fit. Lube it all and install control arms with modified bushings using shims or washers as shims to take up the space the teeth you removed occupied. A good Variable Rate front coil as made by MOOG etc for the SB car should also help.

For shocks a good adjustable front from Strange is great but you can also do it poor boy style by either buying the lightest duty cheap shock you can find or by going to junk yard and trying the shocks by hand until you find two with similar feel that is not worn out but is not super stiff either.

All of that extra work will give you much quicker front suspension rise if you need it than the 90/10 gave and you can better control the car when it comes down and it will not unlad the rear tires plus it will handle much better all the way down the track.

Ed
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Old 06-05-2008, 01:34 AM
  #13  
edvancedengines
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How do we know if we have the correct spring rates;

To begin with we need to understand tha the spring in a drag car has only two functions.

Support the weight of the car up to the starting line.
Give as smooth of a ride aas possible while going down the track.
Possibly a third function is to support the additional weight during weight transfer.

If you can not adjust lower spring adjustment enough for there to be 75% maximum, to 62.5% minimum of the total shock travel inside the shock while car is sitting at rest with all weight in it including driver, you have the wrong springs for the car.

Usually a 2900 to 3000 lb car will want between a 130# to a 145# rear spring on it, but that is never absolute. I know Outlaw 3,000 lb cars working well with 150# springs even. You can not go by just the rear weight to guess what springs you need. Too many other thing figure in, such as the exact shock mount placement in relation to center of axle, Shock mounting angles if any,

You let the car tell you what it wants and you can do that without ever going down the track. At all times you want to keep enough compression available for car to sink on shocks some when front weight is transfered to rear by wheelstands and/or accelleration forces which shove a bunch of weight to the rear even if no wheelstand. You also need enough compresion to allow a good smooth ride down the track. Bottoming or topping a shock out is a sure fire way to unload tires and if at high speed to crash.

Support car on all 4 wheels so you can get under it. Disconnect anti_roll bar on one side (if equipped) just to be sure it is not interfering. adjust the bottom spring adjusters all the way even on both sides, doesn't matter right now how high or low. Measure how much of the shock ram is sticking out of the shock. If more than 50% of the total travel is outside the shock, you need to adjust spring adjusters down so that you will only have appx 25% to 37.5% of the total shock travel sticking out. If you can't and at all the way down on adjusters, that means the spring is too stiff. If you have adjusted the lower spring adjusters as high as you can and you still can not get at least 37.5% to 25% of the total shock travel to stick out of the shock, that spring is far too light and the shock will bottom out while lanuching and while going down track when it encounters any sort of bumps.

The more rear travel the shocks have available the bettter it is to tune. At one time people were using shocks with 5 inches total travel in the rear. That does not allow much room for any error. 6 inches is far better and over 6 inches is even better. Problem is that the longer travel shocks do require more room to mount.

I will use the 6 inch travel shock as my example;

Ideal will be 1.500 to 2.25 inches of ram inside the shock I can not accept anything else if I am tuning the car.

This tolerance does allow it to work with more than one spring rate spring becuase of the lower spring mount adjustability.

lol
I do believe I will be adding this into my 4 link article at Racing Junk. I did touch on it but not this much.

Hope this helps you.

Oh' A ladder Bar car will need to hit the tires a little harder than a 4 link car will becuase of the difference in how they work.

I see that you are also expermenting with power adders etc. Know this, no matter how crazy and backwards it wiill sound. The more you increase power to the rear wheels the less suspension action you want front and rear.

Ed
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Old 11-18-2008, 08:11 AM
  #14  
Curleys
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I didnt know of thsi forum, until someone on another forum posted a link to this article specifically. All I can say is THANKS! As others have said, I saved it to my computer and printed it as well.
My question is in regards to mounting of rear shocks. I think you mentioned we could talk about it if someone wanted to...so can we? The car we run now was built in Florida, and it is the first car I have seen with two different top holes to mount the rear shock. One almost vertical, and one more angled. What differences does this make?
Thanks again!
Kyle
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Old 04-11-2009, 06:47 AM
  #15  
markthespark
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Thanks for the info. I have a better understanding how everything works. So maney people are afraid to adjust the bars because they do not know what they are doing. 4 out of 5 people at the track will tell you a differant answer about tuning a 4-link. I have sent this to about 30 people I know so they can understand it also. Posted on differant sites about it also, should be getting new members signning up, because I think when people see the post they will also want to read it. Thanks again, and please post more info on Drag Racing, Thanks
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Old 04-22-2009, 06:51 PM
  #16  
star393
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Dear Ed
Man your nailing it for so many people , Your 100 % correct about so little info out there on this subject, ive been pulling my hair out always looking, Chrylser put together a great book in the 70,s that you mentioned about suspension and was the only book i ever new about. Took Dave Morgans classes, alittle more help, but best thing for me was to close my eyes and knowing what every part of the cars does encluding the propeller effect of the rear end (if not attached) and immaginary lines of force thur bars and time on the track. From the 60,s to now like you, experance is the teacher. I have employed computer program and that nails alot less track testing time a bunch.
Hope this email finds you in better health and sounds like always great spirits, Thanks for your wonderful time helping the next generation. You are a legend though you may not admit it ,in your time as well.
God Speed and dont forget them push ups TROOPER. Welcome HOME

Douglas aka Star393 WWW.FriedbergRacing.com
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Old 05-27-2009, 08:42 PM
  #17  
ashbros
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I have read this post atleast 5 times. Really makes the old clock start ticking.

I just started a backhalf on a 70 chevelle I am going to turn into a pro-streeter. Been tossing around 4 link vs. ladder bar and I planned on installing an anti roll regardless of which application I used.
But, because of this thread I plan to do more reasearch and cross check the info.

What an abundant amount of good solid info. Sounds like you've hit the nail right on the head.

Thanks a million!!!!!
ashbros
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Old 05-27-2009, 08:43 PM
  #18  
ashbros
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By the way, When is your book going to be published.

Hats off to you..........

Good Luck
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Old 06-12-2010, 03:16 PM
  #19  
GeraldW
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where may i find this article?
thanks
gw
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Old 06-16-2010, 04:12 PM
  #20  
travis91
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I would also love to read this article as I am working on different settings for my 4link.
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