Discussion of Chassis Setup for 8 Sec. Assault

[Alky V6]

I thought I'd start a thread to discuss chassis setup theory and practice for G bodies that are looking at the 8s or quicker in the 1/4.
I'm hoping that much of the discussion will involve the use of the GM style 4-link, but it's open to any chassis configuration and any level of modification.
The discussion will include every aspect of chassis setup for drag racing. Rear suspension, front suspension, brakes, brake balancing, alignment, suspension loading, roll bar setting, setting and adjusting corner weights, calculating IC and adjusting it, calculating center of gravity, to name just a few areas, and sharing the types of floor setups, equipment, software and information references that people are using to accomplish their chassis tuning. Stories of people's experiences with different chassis setups. What worked, what didn't, what to stay away from, what to work towards.
I understand that one chassis setup is not going to work for everyone, and more than one chassis setup will do well to get the job done. I'm just looking to share ideas and, as usual, learn by sharing.

To throw a bone out first, I'd like to ask what people think of using a different instant center (IC) for the left and right side of the car to control body roll during the launch?

 

[turboc87gn]

interesting subd...

 

[cruzn57]

very good post!

I feel there are multiple thoughts on body roll.
using different instant centers is one method, but does it load the tires unequally? causing the car to go left or right? and down tract what is the effect?
using the anti roll bar is another, but.. does it uses energy ( horse power?) to resist roll or twist? and again down track?
another method is to preload the chassis ( via spring adjustment) again does this affect tracking or drivability down the track?
I don't think any ONE way is better for all cars, I feel use what works and is comfortable for your car.
I'm hoping we can get alot of input concerning this issue, Jeff Rand and I have been having some interesting discussions on this very subject.
spring pressures, shock rebound/ dampening, spring stored energy, does a stiff rear spring resist weight transfer?
Lots of thought in this area!

 

[Alky V6]

I'm in the process now of mapping out all the suspension points and will be scaling the car soon. As soon as I have some interesting screen shots, I'll share them. I've finished mapping the rear suspension points and there are some interesting findings from that. The launch of the car, up to this point has been an absolute dream, and some of the things I found out after mapping the rear suspension leaves big question marks. One big question being, if it works this good with the setup this way, what would it do if I did this change?

I'm using Performance Trends' Suspension Analyzer v2.0, and 4 Link Calculator v2.0. I'm planning to lower the front end and wanted to see how that would affect the other dynamics of the suspension. The software will allow me to easily visualize the changes.

One more thing. Mapping out the front end suspension points is a major pain in the azusa.

 

[Alky V6]

OEM style, double A-arm, G body front end.
From a stability standpoint. Is it best to have the lower control arm frame mounting points and lower spindle ball joint on a parallel plane with the ground?
By lowering the front end using adjustable springs (coil over shocks), this would put the lower spindle ball joint on a higher plane than the A-arm mounting points. Is this not the suggested way to do this? Is there an excepted maximum limit for lowering the front end this way?
Is there a limit as to how far you can go lowering the car using the springs?
When would be the point where a drop spindle would be preferrable versus using the springs to lower the front end riding height?
How much would lowering the front end using the springs affect steering in an emergency situation?

 

[charlief1]

One of the biggest issues you encounter with a metric chasis is the location of the upper control arms and the spindles Donnie. I've been looking at it myself and may have a solution that a friend pointed out. It does require you to relocate the upper mount so you can get the most benifit out of it. One of my aquaintances has the jig and the shop that does this. It's not so you can "donk" a car (God forbid please), it's so you can change the characteristics of the handling. You can make it lay over or stand up better. Kind of pricy unless you've got a dedicated race car though.

 

[Alky V6]

One of the biggest issues you encounter with a metric chasis is the location of the upper control arms and the spindles Donnie. I've been looking at it myself and may have a solution that a friend pointed out. It does require you to relocate the upper mount so you can get the most benifit out of it. One of my aquaintances has the jig and the shop that does this. It's not so you can "donk" a car (God forbid please), it's so you can change the characteristics of the handling. You can make it lay over or stand up better. Kind of pricy unless you've got a dedicated race car though.

What exactly is the problem with the upper A arm and the spindle? Are you referring to straight line performance? Front end rise during launch, dive during braking? Or are you mainly referring to cornering performance?
I'm strictly interested in straight line performance, with fair to good safety manners if the car were to get out of shape. Making a car corner is a completely different world that I don't think we need to get into inorder to end up with good straight line performance out of the car. Or am I wrong? Please correct me if I'm wrong.

 

[charlief1]

You have to remember that the chasis and suspension react in a simular manor whether it's going strait or around a corner Donnie. When the metric chasis lifts on a launch the tires go into a camber change, not to mention the bump steer it experiences. You can correct some of this by relocating the upper mount so it's minimized. This will allow you to go straighter down the track and make better times. The only difference between going around a corner and going straight is the way the G forces and chasis flex make the car behave.

 

[Darkcyde]

following the thread, saw this video and it reminded me of it

YouTube - VL Turbo goes sidways on launch

!

 

[Alky V6]

So if you put travel limiters on the front end, set the toe with a certain amount of rise to simulate the attitude of the car during most of the run, would this cut down the bad characteristics to an acceptable level? I really don't see a lot of people relocating their upper A-arm mounts.

 

[Alky V6]

following the thread, saw this video and it reminded me of it

YouTube - VL Turbo goes sidways on launch

!

I think we can classify that as a fine example of a setup we want to steer clear of.

 

[charlief1]

So if you put travel limiters on the front end, set the toe with a certain amount of rise to simulate the attitude of the car during most of the run, would this cut down the bad characteristics to an acceptable level? I really don't see a lot of people relocating their upper A-arm mounts.

Limit you down travel and it should help you some Donnie, but to really make it more effective then get the fully adjustable uppers. I'll be talking to my friend when I get ready to do my control arms so I can relocate them. I don't fit in any class the the turbo Buicks run so I'm pretty much like you. Bracket racing.:frown:

I think we can classify that as a fine example of a setup we want to steer clear of.

LOL So true. Looks like he's running a Chrysler rear in the car the way it's behaving.:biggrin:

 

[scot w.]

Interesting!

 

[SS/GN]

So if you put travel limiters on the front end, set the toe with a certain amount of rise to simulate the attitude of the car during most of the run, would this cut down the bad characteristics to an acceptable level? I really don't see a lot of people relocating their upper A-arm mounts.

Liimiters are a good idea,we found on bad tracks it hurt hook by limiting weight transfer.On a good track we can tighten up the front shocks and tie the front down with no problem:biggrin:,not so on a bad track.Great thread keep it going.

Kevin

 

[Alky V6]

Sorry for not updating. I've been figuring out how to easily and cheaply map the upper A-arm locations. I think I've figured out a tool for doing that and I've been fabricatiing it.

 

[charlief1]

I'll be waiting on what you find Donnie.

 

[Alky V6]

I finally got around to finishing the mapping of the suspension points. Right away, I could see that I need to lower the front end 1" to get the lower ball joint on the same horizontal plane as the lower control arm mounting points, and get the tie rods more parallel to the ground.

I'm going to be busy studying up on front end terminology and preferred adjustments for the alignment.

Screen shots coming soon.

 

[Alky V6]

Need some help from experienced drag alignment fellas.
If one wanted to control the left front rise at launch due to engine torque in an effort to keep the front end level during launch, where would be the best place for the front end roll center? How high off the ground?

How I understand it, the roll center is a point about which the car rolls in the corners. The farther right the roll center, the less the right moves up and down during cornering (circle track stuff). I'm wondering how placement of the roll center would affect front end rise during a straight line take off under WOT. Would it work the same? If the roll center were placed towards the left side of the car, would the left side tend to move up and down less under a straight line leave with lots of engine torque that would tend to want to lift the left side?

Definition of terms.
Roll Center: calculated to be the intersection of imaginary lines connecting the tire contact patch to the front end instant centers.
Front end instant centers: an imaginary point that is the intersection of extension lines from the upper and lower A arms.

 

[Alky V6]

Rear end instant center.
If one were having issues on the top end with traction, but the launch was good, where would one want to move the rear IC, if presently the IC is just in front of the center of gravity? Anti-squat value is 100%. Or, is the IC not the issue on the top end and rear shock adjustment is the place to concentrate the effort?

 

[Alky V6]

Here are some front end screen shots. The first picture will be the present setup with the proposed setup following it.
The change between the two is a .80" drop in the front ride height by using the front springs. Adjustable coilover shocks.

This view is looking at the front end from the rear of the car as the driver would. The right side of the picture is the right side of the car.