Lowering Springs and Drag racing

Hey Don, I think the reason you are putting down some serious times is that your uppercotrol arm mounts are 1" higher. Does your car launch pretty hard? Is the car getting a little squirrely on you at the end of the track?

I am of the opinion that if you are running an HR bar, then bags are noto nessessary for mitigating the twist effect from the rotational torque. I however like you idea of using them as insurance for your tires.

I think proper suspension tuning with our cars will involve proper spring rates, adjustable shocks and altered Instant centers.

Don, why are you running stock height anyways?
When I was a kid I ran a 68 Chevelle with stock suspension. The GN suspension is similar, if not identical to the Chevelle. The stock ride height has always served me well. Like was stated earlier, when you lower the car it will screw up your IC, CG, spring rates, etc. My opinion is, if you're going to lower the car for some real serious performance, aero, you need to switch over to a more adjustable suspension system such as a 4 link and panhard bar, and you will certainly need to be more studied on suspension setup.
 
Best 60' has been 1.28.

:eek:
Do you think there's more to be had out of your suspension setup? I mean, a 1.28 60 foot...that's unreal! Hell I'd be happy if I could just squeeze out a 1.50 60' on mine!
 
Hey Don, I think the reason you are putting down some serious times is that your uppercotrol arm mounts are 1" higher. Does your car launch pretty hard? Is the car getting a little squirrely on you at the end of the track?

I am of the opinion that if you are running an HR bar, then bags are noto nessessary for mitigating the twist effect from the rotational torque. I however like you idea of using them as insurance for your tires.

I think proper suspension tuning with our cars will involve proper spring rates, adjustable shocks and altered Instant centers.

Don, why are you running stock height anyways?
To answer the first two questions.
Yes, it plants the tires pretty well.
With the old setup, if I pushed the boost to max, yes, it was pretty slippery feeling on a well prepped track. On a badly prepped track, it was impossible.
 
Rodney, Don's suspension is a stock type setup, but the geometry of it is much different, thus his improved 60' times.

Don, i am just of the opinion that GM did not design these cars to their fll potential out of the box, thus our need to tinker. Now your 60' times are retty good, and i do not think you would of been able repeat these numbers with geomertically stock style setup. I just think there is room for improvement, and if it means cutting up some brackets, then let's start cutting.
 
There are some aftermarket brackets that can be fitted to an OEM 12 bolt rearend to raise the upper control arm mounting locations at the rearend. I don't know if they're available for the 10 bolt housing.
 
I've said it before but no one ever listens. Find a dirt track shop that can scale your car and find out what each corner weighs, as well as your front to rear ratio and side to side ratio. It will help you balance the car out and you'd be suprised what you will find as far as where your traction is. Granted most of the guys now how to make the a car take a left hand corner but the good ones now how to go down the straights too.
 
Karolko,
I agree that spring rates in these cars do not vary much between a 11 sec and 9 sec car. But shock selection is another story especially if the car is heading to the 9s and or lowered. My car worked very well with plain 90/10 and 50/50's out back and regular ride height.

If the car is low, a double adjustable in the back must be used. This came straight from Todd @ TRZ.
now im saving my pennies..LOL
 
I was playing around with the stock 4 link with the raised upper control arm mounting location at the axle (one inch) and found that the combination of the raised control arm mounting location and lowering the rear of the car 2", moves the anti-squat to 119.9 percent and puts the IC just above the neutral line.
IC length = 46.3"
IC height = 11.2"
As the rear of the car is raised from this 2" lowered position, the IC moves forward just above the neutral line, gradually moving closer to the neutral line and finally intersecting it at the 1" lowered position. As you continue to raise the car to its normal ride height the IC continues to move forward and gradually under the neutral line.

It appears that with the 1" raised mounting location of the upper control arm at the axle, that ride height adjustment at the car rear is a very important tool for adjusting the IC. The range of acceptable IC locations is surprisingly broad with this type of setup. I would imagine that it would not be too hard to come up with the correct IC for most applications by just adjusting the cars ride height at the rear. This is only possible with the raised upper control arm mounting at the axle. I suppose you could instead lower the forward mounting location at the frame around an inch to get the same effect.

That's what your drawing (K) was showing! Hmmm. This stuff ain't that hard after all.

One inch higher mounting location for the upper control arm at the axle, and 2" lower riding height at the rear, and the IC is right in Dave Morgan's suggested box for a 3120 lb car shooting for a 8.55 quarter mile ET. Dang fender lips!
 
Don, Who is dave Morgan, and where can i read what you have read from him?

I like how you have played around with the calculations for IC, but as you are raising or lowering the vehicle, how does the anti squat differ? This also has and effect on how the car will respond, and thus making each position very uniwue unto itself.

I just got backf rom work and have to run out for dinner, but i will post again in a few. My frastration becomes with the CG, and how it is arbitrarily placed at the camshaft height. Has anyone else read this elsewhere, or anything otherwise?
 
Don, Who is dave Morgan, and where can i read what you have read from him?

I like how you have played around with the calculations for IC, but as you are raising or lowering the vehicle, how does the anti squat differ? This also has and effect on how the car will respond, and thus making each position very uniwue unto itself.

I just got backf rom work and have to run out for dinner, but i will post again in a few. My frastration becomes with the CG, and how it is arbitrarily placed at the camshaft height. Has anyone else read this elsewhere, or anything otherwise?

Today I realized that I had purchased a copy of 4-link from Performance Trends awhile back. I just never got around to playing with it. I checked my perf trends programs folder and there it sat, so I was right on it. It comes with an example of a GN, so I called it up and started playing with it.
22 inches seems to be the norm CG for a GN. I've seen that suggestion a few times.
I just got done double checking the height on all the attachment points and they were only slightly off. New info below.
As my ride height sits now the IC is 87.8 L, 17.9 H, a/s is 97.1%.

Lowering the rear ride height .20" will give me an IC 77.2 L, 16.2 H, a/s 100.7%.

Lowering the rear ride height .60" will put the IC vertical with CG at 62 L, 13.9" H, a/s 108%.

Lowering the rear ride height 1.40" will give me an IC 44.1 L, 11.2 H, a/s 124.3%. This would be in the Dave Morgan suggested box for a weight of 3140 and an ET target of 8.5 to 9.0 for the 1/4 mile.

I have a fender lip to tire clearance of about 2" to play with. I think the ATR sway bar is putting a bind on the links that causes the bar to hold the car up higher. I'm going to take the sway bar off tomorrow to see if it drops the ride height in the rear a little.
 
Don what type of percent will those be for IC. Can you show me you calculation. Is it the distance from the CG to the center of the rear axle divided by the IC length. Or 1.4" lowered vehicles, the IC seems to be really short.

Just so i get this straight, 22" will be the CG height for a fatory height vehicle correct? If i lower the vehicle 1.4", the ne CG will be 20.6", and that will be my new number to do calculations with?

I would love to get that program off of you somehow, and where do i find this article from Dave?
 
Don what type of percent will those be for IC. Can you show me you calculation. Is it the distance from the CG to the center of the rear axle divided by the IC length. Or 1.4" lowered vehicles, the IC seems to be really short.

Just so i get this straight, 22" will be the CG height for a fatory height vehicle correct? If i lower the vehicle 1.4", the ne CG will be 20.6", and that will be my new number to do calculations with?

I would love to get that program off of you somehow, and where do i find this article from Dave?

The length (L) is inches from the center of the rear axle to IC in a straight horizontal line. The height (H) is from the ground to the IC in a straight vertical line.

22" is the height of the CG for a factory car. If you install larger diameter tires, front or rear or both, the CG will be higher accordingly. If you lower the car by springs, the CG will also be lower by the amount that the springs lower the car.

Dave Morgan is the author of 'Doorslammers: The Chassis Book'. Dave Morgan's IC suggestions are incorporated into the 4 link Calculator.

The program is very enlightening. You must get a copy.
 
Does anyone have a supplier and part number for a rear spring that will lower the car 1" from stock?
 
What do you guys think about using those pinching devices to squeeze the springs to lower the rear?
 
I tried a set of simple spring compressing clamps, one on each side to lower the car 1". It worked pretty good. Very inexpensive too. I think I'm going to get another set so I can use the two clamps to effectively change the spring rate by how they're spaced across from each other on the same coil. Using two clamps will also divide the work each has to do to lower the car the target one inch.
 
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