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 Post subject: Shorten WB on a 4 link?
 Post Posted: Tue Mar 08, 2011 10:14 am 
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Well since winter is ending here in the Northeast I decided I better get the car out of the trailer and decide what to do with my suspension to make the car work better this year. Really not looking forward to it....

If anyone remembers I have a nose heavy Big block 1968 Dart that has 4 link suspension and cant get it to hook consistently on the warmer summertime track conditions.

Looking things over last night I have enough room that I could shorten the wheel base 1 inch by shortening the link bars and moving the rear forward..

Would that have the same effect as moving the engine back 1 inch?

Doing that would pivot the bottom shock mount forward 1 inch and put the coil overs on a slight angle. Could I leave it that way or should I extend the mounts and square the shocks back up?

Thanks!


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 Post Posted: Tue Mar 08, 2011 11:33 am 
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I have a friend that did something similar to a Camaro that he was class racing. He moved the rear axle forward something like 1/2" and moved the front suspension by slotting the lower control arm mounting points and adjusting the upper. Basically he moved all the sprung weight back 1/2" and claims it made quite a difference. I think if you just move the rear axle forward it will only make half the difference.

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 Post Posted: Wed Mar 09, 2011 9:36 pm 
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Yes just as Chuck says. Something to think about is raising center of gravity which is often overlooked in favor of front to rear weight. It is very effective at transferring weight to the rear quickly. There are lots of ways to do it, raise engine if possible. Your seat, Fuel tank, Batteries. Depending on where you are, it sometimes don't take much.

You will be ok on the coil overs. It won't make a big difference till you get to about 15 degrees.

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 Post Posted: Wed Mar 09, 2011 11:46 pm 
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I should cut the firewall and tunnel out of it and raise and set back the engine while I am at it but man, that's going to be a lot of work.


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 Post Posted: Thu Mar 10, 2011 7:13 pm 
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Moving the diff forward 1" will have more effect than moving the engine back 1". Moving the diff changes the axle relationship the CG where as moving the engine is not moving the CG much, the engine is only a component of the Whole cars CG. But i see no reason to do either, just set the 4 link to a shorter IC, if you have already tried that and it maybe it became too violent then make brackets that bolt into the existing brackets and move the Diff upper mounts and test also the upper chassis mounts with new locations.


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 Post Posted: Thu Mar 10, 2011 7:39 pm 
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What kind of springs are you running on the front and rear of this chassis? Shocks? Are you running a stock front stub or not? What is the IC of this car and how high off the ground is it?

Don

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 Post Posted: Sat Mar 19, 2011 10:45 pm 
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I went ahead and shortened it 1 inch and got to run it today. Air was good and got the best 60 ft ever with it at 1.387....

Here is a video of the pass.....

http://www.metacafe.com/w/6133525

Sorry about the adds but at least Meta cafe doesnt lag bad like photobucket sometimes.


Quote:
What kind of springs are you running on the front and rear of this chassis? Shocks? Are you running a stock front stub or not?

Front is stock suspension with Mopar "drag" torsion bars and Koni adjustable drag shocks. Alot of stored energy with the torsion bars cranked up and front shocks loose on extension.
Rear are double adjustable AFCO's with 125lb springs.

What is the IC of this car and how high off the ground is it?

Right now the IC is 51.5 out and 8 inches up. Puts my IC slightly above the neutral line at 102 antisquat. I ran the shocks loose on the extension today at only 2 clicks.

The biggest thing I am struggling with is the fact that this car is nose heavy at 1654lb on the front, and 1189 on the rear. Real hard to pick up the front in the first place, and real hard to hold it up once the weight transfers.

Car has a lot of front end travel too with the stock suspension. Don,t know if this is causing problems or not. Could try limiting the front travel but anytime I ever dont it on a drag car it hurt traction.....






http://www.metacafe.com/w/6133525


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 Post Posted: Sun Mar 04, 2012 8:48 am 
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Is this with a transbrake or are you footbraking it? I want to say footbrakin it! What rpm are you launching at? what stall on the converter?

Here is what was happening to me, granted my chassis is a whole lot different then yours, but, I am also above my nuetral line and a few inches in front of my C/G too, and 1745lbs. up front vs. 14??lbs in the rear, and as much as I tried to make the chassis do what I wanted, it was useless, and for the simple reason, the engine just didn't make enough power or torque to do what I wanted. It definetly is a balancing act for all these chassis's, and we as racers just need to find the sweet spot is all. One thing also about my hunk of scrap iron is, I have a long wheelbase, and setting my rear 4 link to conventional setting like most people have(ie-bottom bar level, and top bar on a front down angle) just didn't work, now, when I put the I/C up above the nuetral line and in front, and above my C/G, THAT'S where my things changed to the good!!! =; well, plus I added 200hp worth of spray too O:) :- :-$ so additional power & torque changed my whole setup on my chassis to the good, I just needed more power & torque! plain and simple. I have learned that each chassis requires a specific amount of torque to make it do what it does, harnessing more torque will change things, and sometimes not to the good, but mostly to the good. This is info that I have gathered with my chassis and it should apply to all others, but again, to find the sweet spot is the key imo...One weekend or probably more then just one weekend, I want to play with my 4 link settings and try to make it work in conventional settings as mentioned above and see what it takes to adj. for the same outcome I have now. I know it can be done, but I won't change the whole chassis weights around and get too exotic with the suspension changes unless I can make gains right away.

That's why I asked about launch rpm and converter info. Have you tried leaving at a higher rpm(if possible) and see what that does? Another idea is to keep tightening the rear extension on the shocks and keep an eye on the 60 ft's. and that should help also, one way or the other the chassis will tell you what it likes with a few changes.

Good job on the new best 60ft. too \:D/ that always puts a smile on one's face ;-)

Ooh, one other question, have you ever launched off of idle? and then stab it??? I would like to know what the flash of the converter is and you have to watch the tach, get a video of the tach, or have a memory tach to playback the run as it may be too quick to see. just another thought on a Sunday morning with no racing on tv and too much coffee :-$

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