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jhnss396 07-04-2008 07:30 AM

Chassis Flex
Need some advice on why my Don Davis roadster lifts the left wheel more then the right (chassis flex). What do I need to the 4-link? The only sollution I found is to lower the ic. Which means lowering the front of both bars. It launches good and straight. 632 ci, 1.16 60 foot, 7.99 in 1/4 mile @168, 4000 launch rpm. I'll include some picture links. Click album.

topcat572 07-04-2008 08:23 AM

To me it looks good. I think the 60 fts are decent. I dont think Your flexing, I guess the term I would use is yawing. Look at my roadster in Topcat572 hot rods in show offs. Thats a good example of yawing, very little flex involved,my opinion. We actually had photos of it leaving on 1 wheel. 1.19 shorts with a 468. I wouldnt mess with the 4 link, small shock changes may help if it really bothers You. :wink:

promod45 07-04-2008 11:57 AM

do you have a anti roll device in the rear

jhnss396 07-04-2008 06:22 PM

No anti roll bar. Don Davis cars are essentially built to run Super Gas. We've tweak the susspion to run flat out and are trying to fine tune it. Watched a lot of Super Stockers that pull the wheels up with no chassis flex. When we got the car we guessed it was set up right and nearly put it on its bumper. We adjusted the ic down which helped out a bunch. I have one more hole left in the front of the 4-link to adjust to. I guess I could try it and find out what happens.

edvancedengines 07-05-2008 04:45 AM

Your chassis is not looking like it is flexing. It looks good.

The suspension looks like it does have a little bit of a barrel roll in it, but not bad. By looking at it I would say that your bottom bars are close to level currently.

I could guess that moving your I.C down slightly with bottom and top bar down one hole and a loosening of the shock extension dampening might help and you still have good traction by looking at the pics. The rear suspension is acting too radical in the rear.

Anti-Roll bars are often used as a crutch to band-aid a lack of suspension adjusting capability either in the car but usually in the chassis adjuster's brain. They are helpful in fine tuneing a barrel roll condition though.

A 4 Link is not a Ladder Bar and does not work the chassis the same way. The only time a 4 Lnk rear suspension bar angle is the same, right to left is when you are sitting at rest with no torque force applied. As soon as you start the launch the right side and the left side are independent from each other in what happens with bar angles and leverages. I promise you that when you get your front to rise left to right evenly that you will slow the car down.

If the car is launching straigt and true do not adjust any sort of a pre-laod in the bars or with springs.

The way I see it is you are not radically lifting the left front tire as compared to the right front. It is an illusion you see. What is happening is the right rear tire is being pulled up in the fender by bar angle with torque applied and the chassis is stiff enough so the left front is rising more. At the same time the left rear tire is being pushed downward away from the fender by the change in bar angles with torque applied.

That is nothing but the laws of physics in motion working the way it should. by adjusting the bottom bar angle to be lower in the front you are counteracting some of the right to left difference in angles while launching.

If you know what you are doing you can do an assemetric left to right suspension adjutment but be careful. At times what seems to be good for the launch can throw you at the high end when torque unloads and you are trying to slow down with a car pulling to the side. It is all in the finese of making tiny adjustments and knowing in advance what you adjust will do from one end to the other.


edvancedengines 07-05-2008 04:54 AM

Racefab57 07-06-2008 09:05 AM

Ed is the MAN, listen to him!!!!!!!!!!!!!!David.

Bubstr 07-07-2008 09:29 AM

I basically agree with Ed. This is torque roll and because you don't have chassis flex is why you see it.

Any real pinpoint help as far as setting go would be in the crystal ball area of chassis set up, but with some good guesses I would start by dropping rear ride hight about a half inch in the rear and putting a very little preload on upper right bar. Say about a 1/4 to 1/2 flat shorter, and see what you have. If you still get roll add more preload. when it levels out look at compression or separation in rear. You want neither.

While Torque roll in it's self doesn't indicate better traction on one slick over the other, it will change the IC from side to side and that could and will change pressure on them contact patches.

johnracer 07-08-2008 05:44 AM

Originally Posted by edvancedengines

Ed, sent you a pm. Thanks,

shawnp 07-14-2008 04:41 PM

Do any of you think that possibly lengthing the top right bar one flat would help?

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