To relocate our moment center,...
To relocate our moment center, we needed to construct new mounting holes in our upper vertical tubing. This provided more arm angle to improve the location and migration of the MC.
The axle wrap-up is controlled by a unique design of pull bar built by Bert that we discovered some 10 years ago and one that I like. Then we tested it at Eldora and gained 3/10 in a back to back test. The data off the sensors we had installed on the link showed that it worked to control wheel spin all of the way around the track where a simpler design became fully extended and solid soon after power was applied.
The speed of movement on return to static position, when the car is off the throttle and entering the turns, is controlled by a pair of AFCO shocks specially designed for this task. The rates are spoken as being approximately 10 percent out and 90 percent in. This means that they provide very little resistance to being extended when the car accelerates, and considerable resistance to compression to control the force of the 3,500 pound spring in the pull bar as the driver enters the turn.
We then aligned our rearend in the car. The dirt chassis are not easy to use for alignment because there isn't any real symmetry between the two sides of the "frame." So, we aligned the right side tires with the front wheels pointed straight ahead and squared the rearend to that line. Our right side tire contact patches are inline and the rearend is at ninety degrees to that.
Another area of racecar geometry that should be evaluated when putting your car together is the driveline geometry. There is a lot to be gained in this area for both performance and reliability. We measured our relationships between the driveshaft and both the pinion and the transmission.
Along with changing the upper...
Along with changing the upper control arm angles, we also installed Mono-Ball ball joints in the lower control arms and spaced them to reduce the angle of the lower arms.
Pinion angle to the ground plane is useless if we don't also measure its relationship to the other driveline components. We started at the transmission and recorded a 1-degree angle with the tail down. The driveshaft measured 2.50 degrees (rear down) and the pinion was at 4.50 degrees down angle. So, our difference at the front of the driveshaft was 1.50 degrees to the transmission tail shaft and 2 degrees at the back of the driveshaft to the pinion shaft.
Our pull bar will be extending approximately 0.50 to 0.75 inches. We did some measuring and calculations and found that the rearend would be rotating to a maximum of 3.5 to 5 degrees. With this amount of rotation and pinion angle change, when the car is accelerating, the pinion, driveshaft, and transmission will be almost inline. Our experts tell us that this is the ideal situation for minimal power loss and therefore maximum rear wheel power.
We set our panhard bar, which is mounted to the right side of the chassis as it is in all Rayburn cars, at 10 1/2 on the left and 13 1/2 on the right. The mounting of the bar on the right side chassis provides a more consistent feel to the driver and a more stable dynamic condition to the car.
This was first tried by Billy Moyer at my urging on a Rayburn car in 1997 at the Hav-A-Tampa Dixie Shootout, the final race of the top Dirt Late Model touring series held at Dixie Speedway in Woodstock, Georgia. I was just plain dumb about dirt cars back then, but I knew that moving the bar to the right side chassis would be more consistent. My buddy Dewayne Ragland insisted that I talk to Billy and he decided to try it on his Rayburn car. It worked quite well. He set fast time, won his heat and the Dash for Cash, as well as the feature race, which clinched his H-A-T championship for the year.