4 link ?

[Ed-vancedEngines]

I Katman,
Hope you recieved my little page in your mail.

A burn-out instruction mini- page or seminar, I think could noy be very correct to try to do because of all of the many a differing variables with different transmission differences, different tires, tracks, track conditions, and even the differences in your tire conditions.

Some simple basics I can write in a post and possibly other members here can add to them or discuss them or feel free to disagree with me.

If anyone watched the TV Episode or the Internet showing of Pinks Tv when Trevin Lindsey in the White 70 Camaro ran against the Chassis shop from, I think it was Conneticut with the sweet BB Chevy Nova was as near of a perfect example as I could use to show how to not do a burnout. On every burn out the driver was coasting out of the water with a little roll of water in front of his tires. His tires were wet when he was trying to launch. ON every pass that car turned the tires several times before they started to hook. He might have won if the driver had done good burouts and the chassis work was tweeked in better. It is rumered here in Dallas that the better car lost. Who knows.

DRivers need to get used to adjusting their burnout proceedures to the varying conditions of track temps, and tire condition, I still see guys doing the hard tire scorching smokey smokey high tire speed burnouts with the big high horsepower cars when the track temps are over 130 degress and even in the 140 degrees their burout proceedures are the same as if the track temps were 80 degrees. When the track is so very hot the tires don't need to be. When both the track and the tires are extremely hot you end up with melted balls or little particles of rubber between them and the friction coefficient is decreased. Hot tracks with good tires, just clean the tires in a medium tire temp burnout.

If you have super sticky rubber compound do quick tire warming burnouts and get ready to run. I used to always do a quick dry hop before pre-staging to check hok. If the hook was not instant I did a couple more. That I only needed to do if the burn out was aborted or went bad. Once you find what is working best for your tires on that track on that day at that time of daty, stick to it. Only change from what was working if the conditions change.

Old tires will need hot and heavy high tire speed burnouits. Some of the medium and hard bracket style compunds will too. Try to if possible not buy slicks just because of the price but try to even be buying a tire that was designed to work for your type of car.

Eveyone has their own burnout style and who am I do say anything. All I am saying is the purpose to do a burn out is to prepare the tire so it is more sticky after the burn out. Coasting through the water with water getting pushed in front of your tires after getting them warm is not the thing to do. I like to see my customers coming out of the water at full power and I love to hear and see the car hook while the tires are still churning. I also do not like very much water on the tires before the burnout. More than once I have had guys back into the water just to get on the forward edge of it and not have to try to dry up a lake while in their burnout. lol

Ed

[BillyShope]

When viewed from the side, the no squat/no rise line (100% anti-squat) passes through the rear tire patch with a tangent (slope) equal to the center of gravity height divided by the wheelbase. (So, at the front tires, the distance upward to the line would be equal to the center of gravity height.)

Again, when viewed from the side, the instant center (IC) is determined by visualizing an intersection of lines through the pivots for the upper and lower links. If the intersection (instant center) is above the no squat/no rise line, the rear of the car will rise on launch; if below, it will squat. To answer your specific question: For a given IC height, the further forward, the more severe the squat. If the link lines are parallel and parallel to the ground, the IC is at infinity and the car will squat severely. If the link lines are parallel, but are also parallel to the no squat/no rise line, the car will neither squat nor rise. (Parallel lines meet at infinity. So, if the parallel line pair are parallel to the ground, they meet with the ground; if parallel to the no squat/no rise line, they meet with the no squat/no rise line.)

The presence of either squat or rise is undesirable in a dragracing car for either causes an oscillatory loading of the rear tires. With either squat or rise, vertical force components are acting between the rear axle assembly and the remainder of the car. If you were to lie on your back beneath your rear bumper, reach up and grasp that bumper, and then pull down, you would be simulating the action between the rear axle assembly and the remainder of the car with squat. You'll notice that the pressure on your back decreases. In fact, if you're acrobatic enough, you can chin yourself on the rear bumper. But, with the larger forces involved in squat, the rear of the car accelerates downward. So, imagine that this has occurred and you're still on your back, pretending that you're the rear axle assembly. The rear of the car is coming down and will crush you unless you can provide sufficient force on the bumper to stop it. Now, the pressure on your back is greater.

Applying these experiences with bumper and back, we see that a car that squats first removes a portion of the loading on the rear tires and then, as the car approaches the bottom-most position, adds to the loading of the rear tires. Since the shock absorbers and friction are acting to stop the motion, the first effect (the unloading) will be greater than the second effect (the loading), but both will continue for a few milliseconds. (Since the greater effect is the first, some prefer a car that rises on launch, but to achieve maximum performance from the tires, you want to avoid "upsetting" them with oscillatory loadings. It is best to totally eliminate squat or rise by placing the IC on the no squat/no rise line.)

Perhaps a more significant problem, with a beam axle RWD car, is the disparity in rear tire loading caused by the driveshaft torque. Many racers attempt to cancel this torque with some form of static preload, but a much more desirable method is to cancel it dynamically. With the proper suspension asymmetry, it is possible to completely cancel the driveshaft torque effect (unloading of the right rear on launch). For more information on the various ways to do this, visit my blog:

http://home.earthlink.net/~whshope

[katman]

Good stuff Guys!!!

Thanks

[Ed-vancedEngines]

Billy did a much better job of explaining the Percentage of Rise as used in theory than anyone I have seen or heard talk about it yet.

Several of his theories do somewhat bewilder me but are still very interesting reading. Dummy me, the engineering descriptions in his tutorials do take a little while for me to grasp. Sometimes the light bulb will go on inside my head and other times it just stays dim.
Ed

[BillyShope]

Several of his theories....
Ed

Appreciated your kind words, Ed, but you expressed a common misconception, regarding engineers, that I thought I'd expand on.

Engineers don't work with theories. Scientists work with theories. A scientist comes up with a theory (or hypothesis). He then uses the "scientific method" to either debunk or prove his theory. If the scientific method verifies his theory, the theory becomes established science and the engineer then comes in to use that established science in a practical manner.

As I said, the misconception is common and, unfortunately, there are those who use this to their advantage. The evolutionist, for instance, will say that evolution is established science when, indeed, it could never be. The scientific method cannot be used to test a hypothesis involving a unique event. As an example, a voice from the heavens could be heard 'round the world, saying, "Tomorrow, I will create millions of animals with seven legs and having purple polka dots." After the seven-legged animals suddenly appear, the evolutionist would be quite justified, from a scientific viewpoint, in saying, "Yes, the seven-legged animals were created, but everything else came about through natural processes over billions of years." So, both evolutionism and creationism are based on belief systems and constitute what are more correctly called "models." These models are useful in the interpretation of observations, but they are distinct from established science and should never be accepted as such. (In case you're wondering, I personally find too many problems with the evolution model and totally accept the creation model.)

The mistakes made by engineers, then, are either incorrect applications of established science or calculation errors, with the latter being the more frequent. The bases for my spreadsheets are rules of kinematics and dynamics, which are usually taught to the second or third year engineering student. The solutions of the equation sets require my remembering the algebraic manipulations taught me in high school. And, there are times when I wish I had a high school student at my side to keep me from making a silly mistake!

[toddcalo]

Thanks for all the help I will post my wheel wts and cg later tonight Got to get back to work

[toddcalo]

Well here it goes left frt 793 rt frt 697 lt rear 671 rt rear 699 left side wt 1464 51.1% right side 48.9 % cross wt left front to right rear 1485 52.2 % cross wt right front to left rear 1368 47.8% Total wt 2853 with me in car I had to move my battery and put some wedge in it to get the right rear wt where its at (a little heavier on the right should help with bite on the right rear) . Center of gravity is 54 inches back from the center of the front tire approximatley 18 inches off the ground using the camshaft centerline method. I will post control arm positions in a little while ,I will say I am limited at this time on the range of adjustments I can make .

[BillyShope]

I used the spreadsheet at my blog:

http://home.earthlink.net/~whshope

to determine the necessary wheel loadings to achieve equal rear tire loading on launch. Since you mentioned adding wedge, I'm assuming you have adjustable coilovers on all four corners and can, therefore, achieve the following corner weights:

LF 895
RF 595
LR 569
RR 801

Since you said the CG was 54 INCHES from the front, I can only assume you've done some serious shortening of the wheelbase and it is now 100 inches.

I'm not familiar with a 5.56 ring and pinion set and assumed you meant a 4.56 ratio.

I used the total of the corner weights (2860) for the total weight.

I used 2.5 for the friction coefficient.

If you don't agree with the input, I'd suggest you go to the spreadsheet at my blog.

[toddcalo]

Bill that is the correct gear ratio 5.56 however I must have figured the cg incorectley because the wheel base is still 112", is a 2.5 friction coefficent what you would expect from a 11 drag tire ? What do you come up with for cg based on my corner wts? can you recomend a instant center location based on the info i have given? is it ok to run as much wedge as your program is suggesting ?Im limited on th adjustments I can make to the 4 link but I can try to get as close as possible. When I was figuring cg I dived the Wheel base by the rear wt % but I guess thats not right, how do you get it? Thanks for your Time , lots of great info on your website

[Ed-vancedEngines]

I don't know. It looks pretty close to me with his current weight distribution figures of fromt to rear.


I copied and re-arranged the text in your post so I could better understnd it.

Well here it goes

left frt 793 rt frt 697
lt rear 671 rt rear 699
left side wt 1464 51.1%
right side 48.9 %

Front 1490
52 %
Rear 1370
48 %
total car 2853

cross wt left front to right rear 1485 52.2 %
cross wt right front to left rear 1368 47.8%
Total wt 2853 with me in car

I had to move my battery and put some wedge in it to get the right rear wt where its at (a little heavier on the right should help with bite on the right rear) .

Center of gravity is 54 inches back from the center of the front tire approximatley 18 inches off the ground using the camshaft centerline method.

I will post control arm positions in a little while ,I will say I am limited at this time on the range of adjustments I can make .

53.76 inches plus 58.24 inches = 112 inches

How can the center of gravity be anything different. That should be the point that would perfctly balance his car with all current weights.

I get exactly 53.76 inches from the front axle centerline and 58.24 inches from the rear axle centerline . linear point of gravity center of front to rear.

Billy,
Do you get a different place the center of gravity would be? I am considering the linear center of gravity as the same as the point of balance while at rest.
Ed

[BillyShope]

The total of the corner weights is 2860 pounds. 47.9% of that is on the rear wheels, so the CG is 47.9% of the wheelbase back from the front wheels. If the CG is 54 inches back from the front wheels, the wheelbase is 113 inches and I haven't a clue as to where I got that 100 inch wheelbase! Even if I had used the front percentage, it comes out to 104 inches. But, I remember it came out to EXACTLY 100 inches. I think I'll throw away my calculator and go back to my slide rule.

Anyway, with the proper input, the required corner weights come out to:

LF 872
RF 618
LR 592
RR 778

I had to bump the friction coefficient up to 2.6 in order to better the reported 60 foot time.

Of course, the answers are still dependent upon a proper value for the roll stiffness distribution and I would suggest that the procedure outlined on another page in my blog be followed to improve the input.

And, in case you're wondering, yes, every spreadsheet has been checked numerous times to avoid the kind of silly error I just made on my hand calculator.

[toddcalo]

Thanks for all the help Bill and Ed do you think 200# difference in rear corner wt and 250# in the front will create any other problems ,any suggestions on instant center location? Thanks

[BillyShope]

Thanks for all the help Bill and Ed do you think 200# difference in rear corner wt and 250# in the front will create any other problems

If you were on an oval or a road course, it would cause all kinds of problems! The car will be loose turning left and tight turning right. During launch at the dragstrip, however, there'll be essentially zero difference in rear corner weight and, since you're accelerating all the way down the strip, the difference never will be as great as the static value. During braking, there will be no effect unless you are close to locking up the rear wheels, at which time the car will tend to pull to the right. Since most of the braking is at the front, this is not a serious problem.

Having said all that, I would still suggest that you cancel at least a part of the driveshaft torque dynamically. See the other pages at my blog for various means of accomplishing this.

...any suggestions on instant center location? Thanks

I would prefer the IC on the no squat/no rise line and at a height equal to the tire radius (to minimize roll steer effects).

[toddcalo]

Thanks Ill give it a try

[BillyShope]

Just to put things in perspective: If each of your front wheels carried 745 pounds and each of your rears 685 (in other words, if everything was nice and symmetrical), the rear loading would be about 1286 pounds on the left and 1066 on the right during launch. So, if you do nothing about canceling the driveshaft torque, it will affect your performance.

Also, I cannot overemphasize the importance of trying out any setup with the traction dyno I describe in my blog.