Center of Gravity 70 c-10

[fuzzy1nickels]

Hello all,

Currently installing suspension on my project (scotts hot rod front ifs and 4-bar rear/ 4" 6" drop). I am doing a 4bar system in the rear and have been doing A TON of research on the measurements and every thing that needs to be taken.

Mainly I am wanting to know if any one has any clues on where the center of gravity is in regards to the vertical direction so I can set my antisquat. I am able to pretty easily find the cg from front to back, but up and down is a real hassle with out a set of scales. If any one could give me a ball park estimate on where it might land, I would greatly appreciate it.

My only guesses so far would be about where the center of the crank shaft is would be a good starting place to look. Thanks for the help

[SCOTI]

Originally Posted by fuzzy1nickels

Hello all,

Currently installing suspension on my project (scotts hot rod front ifs and 4-bar rear/ 4" 6" drop). I am doing a 4bar system in the rear and have been doing A TON of research on the measurements and every thing that needs to be taken.

Mainly I am wanting to know if any one has any clues on where the center of gravity is in regards to the vertical direction so I can set my antisquat. I am able to pretty easily find the cg from front to back, but up and down is a real hassle with out a set of scales. If any one could give me a ball park estimate on where it might land, I would greatly appreciate it.

My only guesses so far would be about where the center of the crank shaft is would be a good starting place to look. Thanks for the help

From stuff I've read, that's the best point to target if you don't have access to scales.

[Keith Seymore]

Originally Posted by fuzzy1nickels

Hello all,

Currently installing suspension on my project (scotts hot rod front ifs and 4-bar rear/ 4" 6" drop). I am doing a 4bar system in the rear and have been doing A TON of research on the measurements and every thing that needs to be taken.

Mainly I am wanting to know if any one has any clues on where the center of gravity is in regards to the vertical direction so I can set my antisquat. I am able to pretty easily find the cg from front to back, but up and down is a real hassle with out a set of scales. If any one could give me a ball park estimate on where it might land, I would greatly appreciate it.

My only guesses so far would be about where the center of the crank shaft is would be a good starting place to look. Thanks for the help

According to Alston Chassis, it is approximated by the height of the center of the camshaft, at the front of the engine.

The only way to determine the height of the CG experimentally is to "tip" the vehicle (fore/aft) and do series of calculations.


Question: how are you determine the CG location front to back without a set of scales?

K

[fuzzy1nickels]

Originally Posted by Keith Seymore

According to Alston Chassis, it is approximated by the height of the center of the camshaft, at the front of the engine.

The only way to determine the height of the CG experimentally is to "tip" the vehicle (fore/aft) and do series of calculations.


Question: how are you determine the CG location front to back without a set of scales?

K

Going to have at it red neck style. Essentially just going to pick it up with two post of the lift and determine the area where it's balanced i.e. if i pick it up a few inches and it falls forward i am obviously not at the cg. and vica versa for the rear. This should get me a solid approximation. I'll post up where about I find my cg this week end when I get the truck in the shop.

[Keith Seymore]

Originally Posted by fuzzy1nickels

Going to have at it red neck style. Essentially just going to pick it up with two post of the lift and determine the area where it's balanced i.e. if i pick it up a few inches and it falls forward i am obviously not at the cg. and vica versa for the rear. This should get me a solid approximation. I'll post up where about I find my cg this week end when I get the truck in the shop.

LOL - that method will certainly work - and has been done that way a time or two on one of my cars...

K

[Keith Seymore]

Found this while looking for something else.

Since it's just you and I here (and Scott) I'll post it here.

This is the story I alluded to in my above post:

Originally Posted by Keith Seymore

One of the things I enjoy about being "my father's son" is finding the little surprises he left behind.

I was in his garage the other day and I found this "well loved" Chassis Service Manual:



...as I was flipping through the pages, I found these sketches:



As you might guess, there's a story there, too.

Originally Posted by Keith Seymore

Dad had the opportunity, through his connections at Royal, to work a little bit with Roger Huntington. For those not familiar with Roger he was a free-lance author and tinker-er, and fancied himself to be somewhat "forward thinking" in the areas of performance and automotive engineering. He probably was, actually, but was crippled by polio and therefore wheelchair bound; as a result he had to live out these theories through others and the subsequent articles.





Recall that the main issue facing these high horsepower cars back then was the lack of traction. Conventional wisdom called for production rear suspensions, as released by the manufacturer, and the addition of "Atlas Bucrons", or some other "soft" compound tire. There were no wrinklewalls, no "fat" tires, no water burnouts, and traction compounds were for the fledgling professional race categories (if at all).

There had been some thought that "longer" rear control arms were better, perhaps resulting from successes with the Swiss Cheese cars and other big Pontiacs. In fact, some work had already been done installing these longer Catalina lower control arms on the smaller intermediate sized GTO's.

Roger proposed that this thinking could be taken to the extreme: if a lower control arm, or traction bar, could be fabricated to attach all the way up at the car's "center of gravity", then that would be ideal, right? So between he and Dad they devised a scheme to fabricate such a device and install it on our GTO. The sketches you see here are the result of that brainstorming session.

The first order of business would be to locate the CG of the car, in the fore/aft direction. Dad had told me previously about jacking the car up, using a small scissors style jack on each side, and moving them forward and rearward along the car until it "balanced" with the front and rear tires off the ground. This would establish the location for the forward attachment point, at each frame rail. Square tubing was used to fabricate the bars themselves and they were clamped to the rear axle tube to secure the rear of the bar.

In short order the new setup was ready for testing. Arrangements were made to rent one of the local tracks and Dad and Roger met there with high hopes and great expectations. After warming the car, Dad proceeding to the starting line for the first test pass. Equipped with a skinny set of M&H "Racemasters" - a couple short, "dry hops" indicated everything was in order - Dad staged the car and the tree came down. Dad launched the car and BOOM!! it immediately spun end for end, moving only a few feet forward and pointing exactly back the way he came. Shaken, Dad "putt-putted" back toward the bleach box area and shut the car off to regain his composure.

After a short break a second run was attempted. Dad tried "driving" the car out (a much less violent launch), but the car never gained traction down the quarter mile, slipping and sliding until the run was finally aborted. The "traction bar" concept seemed to be a dismal and complete failure, after just these two attempted passes.

Today, in hindsight, we can see why these would not work. Per the "doorslammer" chassis guru's, like Chris Alston or Dave Morgan, the instant center of the 4 link rear suspension is driven rearward and down from the production location, providing more "percentage of rise" when compared to the car's center of gravity. Today we would never consider moving the instant center to go directly "through" the heart of the CG; what they had tried out was completely "directionally incorrect".

As has been said before, you can learn as much from your mistakes as from your successes. The rear suspension was returned to it's "production" configuration (ie, control arms attached at their original locations, reworked bushings, air bag located in right rear spring), and it is in this condition that the car ran it's best ET and is how it sits today. It is basically the same setup that I have on my bracket/index car today.

Dad had mentioned that some of the bracketry and holes can still be seen under the car; I haven't checked specifically but the next time it's up in the air I will take a look.

K

[502ms]

That's great info!
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[kpeztruck]

The center drawing on page 1-5 of the shop manual is a good starting point. Any instant center point above the line drawn from bottom of rear tires to top of front tires will promote anti-squat. Anything below will promote squat. The shorter the instant center, the faster and more violent the movement will become. I have found this works very well in "estimating" instant center characteristics. Hope this helps, Paul

[fuzzy1nickels]

I was very blown away about the amount of susepension geometry involved in a 4 link (didn't do enough research prior to buying the kit, but I'm making up for it now). Found this excellent link http://www.baselinesuspensions.com/i...A_Drag_Car.htm dealing with center of gravity and antisquat. I think it's a useful tool for any one building suspension.

Right now the initial plan is to find my center of gravity (close estimate) and set up one hole on my 4 bar for a 35% antisquat and set my springs a bit stiffer (alden full adjustable coil overs) for street and handling applications. I also will create another adjustment hole for about 100% antisquat for drag racing purposes and set the rear springs a bit softer. Hope to achieve both antisquat settings out of the same bracket.

I'll eventually post a thread of my frame build up. Just finished boxing it up and the suspension is about to go on :-)