Suspension question for you engineers out there

[STAGE 2]

Ive done extensive reading about Kirbans GNX suspension and its many advantages when compared to the stock setups on our cars. This of course is not taking into account the crappy quality control which contributed to the many missing parts on turbo regals and GN's.

In kirban's suspension booklet he advises against using the suspension setup for a t-top. I understand that simply by virtue of the fact that there is less of a frame to stabilize the car, there is a greater propensity for body flex and such. However, considering the natural deficiencies of the stock setup, even in its completed form, shouldnt the gnx suspension still be an improvement in the overall structural integrity of the car when launching?

I guess my question comes down to whether or not Kirban's proviso is for liability purposes, or is there a real probability that installing such a setup on a t-top car could result in serious damage when launching either immediately or in the long term?

 

[Roger]

I suggest giving Denis a call. I found him to helpfull & knowlegeable.
Consider a roll bar setup.
I am having too much dificulty justifying the $3k+ to my wife.

 

[lrayzer]

The no T-Top recommendation should be the result of the improved geometry launching the car harder, therefore putting more stress upon the body unless properly prepared.

I fabricate a relocation kit that is easier to install and gives much more adjustment.

The whole goal is to correct the "squat" in the factory suspension.

Brace the frame, add all the bushings, and seat braces etc, and go for it.

 

[Ormand]

GNX Suspension

Not sure that this suspension is much advantage on the strip. Maybe no advantage at all. It is better for handling, though. It's a three link, with track bar, and it should provide better cornering, like the suspension on the F-bodies. Don't see why it would stress the frame or the body any more, though.

 

[bruce]

Originally posted by STAGE 2

Dave Morgan's Book Doorslammers is a really interesting read and is primarily about drag racing.

The GNX setup IMO, will afford less binding as the suspension moves, then the stock stuff. The more responsive the suspension is the better the grip you can get. the better grip you can get is going to apply more bending forces to the chassis. That will transfer more loads into the shell. TTop shell is weaker then the full roof. Your call about the risk of bending things. When in doubt error on the conservative side is my way of thinking.

 

[wfoondirt]

The gnx setup was optimised straight line accel. The torque-arm (not a 3-link, 2 totally different animals) is very short and could cause wheel hop under extreme braking as in road or auto-x racing and there is still some inherant bind in extreme roll situations. The f-body t/a's are almost twice the length and allow for better for/aft movement. But the gnx suspension is definately an improvement over the c4l, with a lower roll center and better ic geometry. The gnx setup will definately launch harder on the strip, possibly even better than the f-bodys because of the short t/a. Whether these forces are enough to damage a t-top car is up in the air. But if your running fast enough to need the gnx suspension most tracks will require a bar anyway. If your determined to do it without a bar i would definately do all the usual bracing and make sure all your body bushings are in good shape (which should be standard procedure with any t-top car IMO, made a world of difference in mine).

Personally i dont think that the kirbans setup is worth the money. It can be done better if someone isn't afraid of a little fabricating.

 

[turbov6joe]

For thousands less, the Wolfe rear suspension for the G bodies is a really good way to lay down the power at the track! If I'm not mistaken, Jack Cotton uses this suspension, give him a call for verification of its worth. The GNX style suspension was originally designed to increase handling in the turns, over that of the factory G body suspension. Personally I own a TTA which has a suspension similiar to the GNX, and it also has its short commings (cheap stamped parts, mushy bushings etc...). I myself am in the process of R&R all of the rear suspension componitry on my TTA to increase its overall handling and launching capabilities. If you have the $$$ to buy the Kirban GNX set-up...go for it. But there are many other cheaper and cost effective ways to address the suspension of the G body IMO. Good luck!

 

[KEVINS]

This is an interesting thread but I feel that I should step in to clarify a few things about the TA's like the GNX and Camaros use. Let me start by identifying a few things that MUST be considered before identifying what is a good Drag Race suspension.
The Instant Center (IC) was mentioned above and the location of this relative to the Center of Gravity (CG) and the Normal Line is critical. If the IC is to far forward from the rear axle (more than 32” or so) and lies below the Normal Line then the AntiSquat (AS) becomes less than 100% which causes the rear of the car to squat which unloads the rear tires. The IC is the front mounting point of the TA. The longer the Torque Arm the less AS there is and the easier the rear tires are unloaded. The GNX Torque Arm is BAD for allowing the car to squat, again unloading the rear tires due to the long TA. In a nut shell the GNX suspension SUCKS for Drag Racing. Give me the factory 4link over the GNX suspension any day.
Is it better than a Camaro? That depends on the location of the Center of Gravity of the car and the IC (length of the TA) location relative to the CG.
Does the TA offer a “better” IC position than the factory 4link suspension? That depends. I have plotted out many GN’s and several of them have the IC BEHIND the car. This is bad. However, adjusting the ride height of the car allows the fine tuning of the IC position and can bring the IC position to a much better location to bring the AS values to a more reasonable location than the TA can achieve. Since the only way to change the IC position of the TA is to mechanically change the front mount position it is limited by how high you can raise the mount. The longer the Torque Arm the HIGHER the mount NEEDS to be to achieve a better IC position.

Hth’s a bit
ks

 

[lrayzer]

You are correct, I have fixed this situation, the right way !