Hey Folks, Im building a tube chassis AWB '62 Nova. Loosely following the Doug Thourley "Chevy II Much".Although, I am trying to keep the spirit of the early funny cars,the car does have some modern concepts and design. It originally was 110" wheel base. The rear is moved ahead a total of 9" and the front tube axle is move a total of 4".So we have a total of 105" The motor is recessed deep into the drivers compartment.But the drivers seat remains in stock location. I can get a measurement of where the motor falls in relation to where it is on the wheel base. I'm building my own ladder bars,and need to know where to mount the front pivot.I have a general understanding of Instant Center and such.But the formula is beyond me. Any help? Thanx, Brandon
http://www.racetec.cc/shope/tim.11.htm Your antisquat line doesn't change with engine set back- it always is directly above the front contact patch at the center of gravity height (calculate that here: http://www.racetec.cc/shope/tim.30.htm) The line running from the rear contact patch (actually about 1.5 inches under the rear contact patch) to the instant center is the antisquat line- set up your chassis based on that line- if you put the ladderbar mount on that line you'll be at 100%antisquat, lower than that line and you'll get rear end squat-higher than that and you'll get rear suspension separation. You probably want lots of neither, and a little bit of separation (greater than 100%antisquat) rick
On the page for calculating C/G. The last input is "Vertical Distance to rear axle center line" I guess while the car is tilted,but What is this measurement? Brandon
A lot of the early cars had lift bars, which looked like welded 2X4's. They were mounted solid to the rear end and the pivot point was the trans X member. My friend has an old Willys drag truck and his lift bars go almost to the firewall.
axleshaft center-to- ground measurement- basically how much you've lifted it when it's compared to the height of the axle center before you lift it- which would be half the tire diameter (radius) if there was no flat spotted contact patch- not sure how to handle that aspect (the flattening of the tire on the ground) once the calculator knows the angle or how high, and the change of weight on the fronts and the initial weight on the rears, it can calculate it. I've not tried this yet, but i'm DYING to know how high my center of gravity is... got the scales, but the car is currently just an empty shell. I'm using lever beams and 4 bathroom scales- just a beam that goes on a bathroom scale with a tire pad 1:4 ratio in between the ends V---=-----------v put the big V pivot on the ground, the tire goes on the equals sign and the little v goes on a bathroom scale- if the ratios are 4:1 and your average scale can handle 300lbs then you're good to go as long as you dont have more than 1200lbs on any one tire. Have to do all 4 at once to get good results. I'll try to post pics- cheaper than electronic scales (well unless they've gotten REAL cheap, lol) rick edit:
My Buddy is an old roundy round guy. He's got some nice digital scales. I used them to 4 corner my other drag car to set preload and such. Brandon
You can do all of the technical calculations but there is no way to know the height of the center of gravity of your car. The "instructions" say to use the center of the engine block as a guestimate. The best rule of thumb for attaching your front eye of the ladder bars is: set the bars with the lower bar of the ladders bars level or horizontal. You will be VERY close to your correct setting. Your front bracket needs to have a hole or two above and below the initial mounting hole--- just in case you need to adjust. Also, build your bars with an adjustment in the lower bar of each ladder bar; it will make things much easier to dial in your car. To make your car go straight, put yourself or identical weight in the driver's seat when loading your ladder bars. When you jack up the rear of the car from the CENTER of the rearend, the back tires should come off the ground at the same time. If you are doing the work without help and you can't put weights in the driver's seat, the left rear tire should come off the groung 1-1 1/2 inches before the passenger side rear tire comes off the ground. This info will help you to set up your car very close to the desired final setting.
not sure which "instructions" you're referring to- this method seems logical, if someone's figured out the spreadsheet calculations to make it work. http://www.racetec.cc/shope/tim.30.htm take weight on 4 tires, then jack up the back a measurable distance, and compare to the weight now on the front tires (which will include some more weight that was on the rear). Wheelbase plus raised rear axle height gives the angle of lift, which is calculated to find the weight shifted onto the front tires, which gives you the height of the center of gravity, as long as the guy writing up the spreadsheet got it right. I'd bet you a coke he did.
Thanx,Ive set up preload on my drag car a few times with this method,but using 4 corner scales to adjust the front end weight from left to right(adj. coil overs). Then load the drivers side with weight,unhook the ladder bar from the passanger side.Jack up the drivers side until the car is level.Then preload the ladder bar until it lines back up in the appropriate hole. But what Im trying to figure out is the length of the ladder bar for the AWB car.With that I need to calculate Instant Center. Brandon
I think that Ive heard that before."Using the center of the motor as an approx. for the height of the CG. Brandon
standard practice i'd heard of was to estimate it at camshaft height (which is pretty much the center of the mill). But that was for a typical OT/Musclecar chassis. Now that my falcon is over 5 foot tall with the engine mounted way up in the air, traditional thinking probably isn't as accurate as measuring,lol. the example in that calculator comes out to 19.9inches, which is most likely based on someone's race car. I think my crankshaft is 28 inches off the ground, my fuel cell is on top of the trunk floor, and my fat ass rides high on the stock bench seat, so i'm sure the vertical CG is way up there. Finding the right instant center is important. I've struggled with this myself, as I plan on the car being a low 10 second ride (all the power my current block will handle). I'm not gonna settle for a under performing "race car" BUT the other goal is to put 2 feet of air under the front tires on a certain private road that we meet at. If the calculator for vert CG is accurate enough, then we can determine our antisquat lines and then know where to mount the multi-position bracket for the ladder bar forward mounts., and dial it in from there... It's getting pretty exciting! Best of luck on your Nova! Pictures, Pictures, Pictures! -rick
"If the calculator for vert CG is accurate enough, then we can determine our antisquat lines and then know where to mount the multi-position bracket for the ladder bar forward mounts., and dial it in from there... It's getting pretty exciting!" That statement right there is convincing enough to do it right! Brandon
Might want to read the rule book, 24" crank maximum height; Get Dave Morgans' book on doorslammer suspension theory. I disagree with some of the notions that he wanders into but it is plenty accurate and does a good job explaining the basics. You can make a scale model of your car, on the shop floor with a keil. Mark the tries (wheelbase), measure to the axles and add it to the floor (axle ht) crawl under and get the pinion ht; trans yoke and crank bolt hts add them to the drawing. Keep adding the major componants and soon you'll have a 1:1 drawing of the car right in front of you on the floor. That is where the tem 'scaling' a car came from, it did not involve weighing the car. When it is down on the floor you can then take 2X4's, whatever, to mockup the traction devices - whatever they may be.
I know it wasn't an AWB but gasser. Teixeira Willys pivot was at the clutch disc or bellhousing area in length. Mounted solid to the rearend with the rear springs floating.
i just built a lower 4 link bar on my willys that is mounted close to the front spring,its across from the bell housing. i rember a guy did the same with a novea and it would always wheelstand leaving the line on its rear bumper..with a mild small block 12 sec. car! im hopeing that it will lift the front easy,it looks like it will work because i can almoast bench press the front off the ground from the center of the car.
I don't think that the length really matters. Look at the ladder bars that are sold by Chassis Engineering, Competition Engineering, etc. They are all approximately 33 1/2 inches long from the rear mounting holes to the front one. And the length really doesn't matter because of the geometry involved. The plane that ladder bar lies on is the important thing. It's all geometry and physics -- (fizix for those of you that went to high schools where testing and assigning grades were discontinued so that some people would not feel bad if they got a bad grade). I highly suggest that you purchase a copy of Dave Morgan's book, "Door Slammers: The Chassis Book". It will explain many of the mysteries of setting up a suspension and it will answer many of your questions. And now you might can get the book on DVD but I am not sure. I bought my book about 20 or so years ago. If you are going to drive your car on the street, I recommend that you use hiem joints on the front of each bar. When you turn into driveways or any place where one side of the car is not level with the other side, the hiem joint will eliminate binding and breaking at the connecting points. When one side of the rearend goes down, it is rotating (or twisting) and the connection point needs to be able to rotate with it. And if you mount the ladder bars so that the front attachment points are close together-- about 6-12 inches apart- it will also lessen the binding. There is one advantage that I know of that is gained by having longer ladder bars-- the longer the bars, the less that the rear axle moves forward and rearward when the body and frame go up and down when hitting bumps, turning in driveways or violently launching the car during drag racing. The drive shaft is gonna move inward and outward of the transmission's tailshaft. You have to allow for this when making your driveshaft but the longer bars cause less travel of the driveshaft. I have 43 1/2 inch long ladder bars on my '34 Ford. It rides very good on the roads and it lifts the front tires when drag racing. My bars are slanted inward at the front and the front attachment points are about 8 inches apart. One other consideration to the length of the bars might be the amount of space you have under your car. A street car needs room for mufflers and tailpipes. Be sure to think about your exhaust system before you make long bars like I have. ALSO, build your bars with an easy adjustment on the lower bars! It will save LOTS of time and trouble when you need to make adjustments for traction and settings.
Without getting all crazy with the math and scales, I'd just balance the car front to back on two jack stands (one under each frame rail)to find the center of gravity.
The method you describe would only define where the horizontal center of gravity lies between the front and rear bumpers. To figure the antisquat line, you need to know the Vertical center of gravity. Between the road and the roof. This allows one to direct suspension forces above or below the rotational axis of the car during a launch. Find the VCG and put a peice of tape that distance off the ground on the fender directly above the front spindle. Then run a string line from that tape mark down to your rear contact patch. That string represents the antisquat line. If your forward ladder bar link (or front leaf spring bushing) is on that line when viewed from the side, then you have 100% antisquat. Instant center above that line (greater than 100% antisqaut) will tend towards body/tire separation, and IC below the line (less than 100% antisquat) will tend towards body squatting on the tires under launch. rick
Ive re read this thead several times and it is really coming to light now. I see what Jingles ment about the length of the bars dosent "really" matter..........as long as the front pivot puts the bars in the correct angle as the anti squat presentage were looking for. Very cool input from everyone, Thanx a ton. Brandon P.S. I got the rear end back from Dutchman today.Its a Dana 60.I had it shortened,35 spline alloy axles made and 9"Ford bearing ends put on. Now I can get to work on the ladder bars.
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