8 second OEM 4 link drag race chassis setup

[Alky V6]

I decided it's a good time to get new numbers on the chassis, after all the changes I've been doing lately.
Total weight w/driver and full tank: 3301.5 lbs.
Percentage of weight on rear: 45.9
Percentage of weight on left: 52.0
Percentage of cross weight: 47.9
Corner weights (lbs.);
LF: 960.0, RF: 826.0
LR: 756.0, RR: 759.5
The rear corner weights are within 3.5 lbs of each other. This was established by measuring rear spring heights alone to set the rear corner weights. Then the corner weights were checked with a scale. Love it when a plan comes together.

Now for an accurate measurement of the rear control arm pickup points. X Y and Z coordinates to be added into the 3D suspension analyzer.

 

[Alky V6]

Wow. Surprise again. I did a much more accurate layout of the rear control arm pickup points. Very interesting results.
This is what I came up with;

Left side: 40.2, 10.23, 127.4
Right side: 41.93, 10.51, 125.5

With .400" of body roll, I get the following;
Left side: 40.88, 10.48, 128.4
Right side: 41.05, 10.23, 124.8

 

[Alky V6]

With a simple drop in the height of the right side upper control arm frame mounting point (the bucket) of only .050" I get the following numbers;
IC length, IC height, Anti-squat %
Left side: 40.2, 10.23, 127.4
Right side: 40.66, 10.49, 129.1

With .200" of body roll;
Left side: 40.54, 10.35, 127.9
Right side: 40.25, 10.35, 128.8

With .400" of body roll;
Left side: 40.88, 10.48, 128.4
Right side: 39.83, 10.22, 128.4

Notice how I'm losing the AS% offset with increasing body roll. Interesting.

 

[Alky V6]

If I simply mirror the right side upper control arm, frame mount coordinates to that of the left side, I end up with this;
IC length, IC height, Anti-squat %
Left side: 40.2, 10.23, 127.4
Right side: 39.26, 10.46, 133.4

With .400" of body roll;
Left side: 40.88, 10.48, 128.4
Right side: 38.49, 10.21, 132.7

The amazing thing is how little of a change in that one coordinate would result in the above specs. The changes needed would be;
Out (X): +.0625"
Height (Y): -.125"
Depth (Z): +.0625"

 

[Alky V6]

If I change the height (Y) coordinate -.0625" instead of -.125", I get the following;
Left side: 40.20, 10.23, 127.4
Right side: 40.73, 10.49, 128.9

With .400" body roll;
Left side: 40.88, 10.48, 128.4
Right side: 39.90, 10.22, 128.2

Dang, I was close. I like this one. Tomorrow, I'll be removing the right side bucket and changing the X, Y, and Z coordinates, each by 1/16".

The anti-squat % figures are very dependent on the accuracy of the center of gravity height spec. I'm using 21.7" height for that spec. For instance, if I am off and the center of gravity height is actually 24", the anti-squat percentages would be more in the range of around 115%. So we can safely say that my AS%s are in the 115-128 range.

 

[Alky V6]

Since I was taking the time to more accurately lay out the control arm mounting points, I went ahead and rechecked the UCA stock frame mounting points. I thought it would be interesting to see where I'm at after all this, in comparison with the original settings with the stock frame mountings and the original mounting locations that came with the Moser housing.
Using the stock frame mounting locations and the mounting locations of the 12 bolt Moser housing as it came from their shop, I get the following specs;
Left side: 46.2, 10.6, 115.4
Right side: 44.7, 10.6, 118.2
Realizing that my CG height could be off, the AS% could be as much as 10% less than shown above. Still, this is a very good starting point for the instant center. This instant center length also happens to be in the Dave Morgan suggested range for a car planning to do an 8.50 ET.

 

[Alky V6]

The IC specs for the right side, when I had the LCA axle mounting lowered about 1/2" from the original Moser mounting point gave the following specs;
Right side: 38.6, 11.0, 142.8

This is the spec the right side had during the latest chassis testing where the car performed the double wheelie on that one high boost launch, on old slicks.

 

[KEVINS]

Don,
Any updates? How's things progressing?

ks

 

[Alky V6]

Don,
Any updates? How's things progressing?

ks

The car is down for engine O/H and upgrading. We're switching over to a set of Stage II heads. Should mean around 300+ more hp.
The last noted suspension changes are still in play. I only got a few launches in with the latest IC setting, but it felt real good. The extended pull felt like it was back. The front end rise was a little more, but not nearly what you would call excessive.

 

[charlief1]

I got notified this time. Glad you're doing a little updating Donie. Are you going to make another intake as well?

 

[Alky V6]

I got notified this time. Glad you're doing a little updating Donie. Are you going to make another intake as well?

The intake and exhaust manifolding will have to be changed.

 

[charlief1]

The intake and exhaust manifolding with have to be changed.

Do a couple more thread in the fab section then Donnie. I like seeing your work and I'm sure others would like to see more of it as well.

 

[Alky V6]

The last launch pic of the car before she was retired for major overhaul. This pic was taken using all the latest suspension settings noted in this thread. The car carried the wheels for a fair distance. 10-15 feet? It wasn't just a quick pop up of the wheels.
Only a relatively small amount of front end travel limiting being used in this launch.

 

[Alky V6]

I should note something now, that I want to check out when the car is back running.
On one of the last runs, as the car launched, it felt like the car wanted to pull to the right slightly, right at the initial hit. That sensation lasted for a split second. As the front end continued to rise, and the wheels left the ground, the car straightened out and pulled out straight. That was only felt on one run.
I suspect a slight anti-roll bar adjustment (more preload on the RR corner) will be needed, if it proves to be a recurring problem.

 

[charlief1]

From the pic it looks like the RF is still hanging just a bit lower Donnie. If that's the case it might be that the RF is causing the slight right drift you're feeling as the car launched. It might be the angle of the pic but something you might want to check.

 

[Alky V6]

From the pic it looks like the RF is still hanging just a bit lower Donnie. If that's the case it might be that the RF is causing the slight right drift you're feeling as the car launched. It might be the angle of the pic but something you might want to check.

With the present suspension settings, the RR corner has very little preload on it. I believe it's at around 3 lbs. If I recall correctly, the ARB is zeroed out, or maybe has 2 flats (1/3 turn) into it. It makes perfect sense to me that I might have to add more ARB preload, if I find that the push to the right at initial hit is a recurring problem. I'm not too worried about it. It was barely detectable. One of those things that's so slight, you kinda pick it up in the back of your mind.
Due to the stiffness of my chassis and the ARB, I don't feel I will be able to remove all body roll at the launch. For one thing, the roll cage does not extend out to include the front clip, so I'm sure a lot of twisting is going on, just in the front end alone. I also feel the ARB may not be stiff enough to remove all body roll associated there. The overall amount of body roll I am getting is acceptable to me.

 

[Alky V6]

If you look closely at the picture in the area of the RR tire clearance to the upper fenderwell lip, you can see that there is about a one finger clearance there. That is about what it is when the car is sitting static. So the amount of body roll and anti-squat in the rear is very acceptable to me. Of course, I would have a better picture of the body roll if I had pics of both sides of the rear.

 

[Alky V6]

In summary, up to this point, the instant center length, instant center height and anti-squat percentage are;
IC length: 40-41"
IC height: 10.2-10.5"
Anti-squat %: 115-130 depending on the actual CG height. Average, 123% AS.

So, what we ended up doing, if we compare these latest numbers to what we had before we started playing with the instant center location, is we shortened the instant center length by 4 to 5 inches, shortened the instant center height by about 1/4 inch and increased the anti-squat by 10-15%.
This seems about right. The major goals were to add a little more anti-squat to get the right rear fender lip off the tire, and maybe get the car to carry the wheels a little longer at the launch at a good controlled height. I think she's there.

 

[Alky V6]

The 41" instant center length corresponds with Dave Morgan's recommendation for a car that weighs 3200 lbs. and performs an E.T. within the range of 9.90-10.60 sec. Dave's recommendations stop at an upper weight limit of 3200 lbs. My car weighs 3300 lbs. More vehicle weight moves Dave's recommendation box back towards the rear of the car. So, if we extrapolate Dave's recommendation pattern, a 41" IC length with a 3300 lb. car would be for a suggested E.T. range of 9.70-10.40 sec. Seems like a reasonable match for a 10.5" rear tire.

My instant center height is .688" higher than it would be if the lower control arm were perfectly level with the ground. The front lower control arm frame mounting is .307" higher off the ground than the rear lower control arm axle mounting.