With the car strapped down for business, we are about to discover a few things about horse
It was exciting news. Gerald Williams of Mid-State Machine called and informed us he had secured a dyno for a day. It was located at the Statesville, North Carolina, shop owned by the legen-dary Winston Cup team owner Travis Carter. Not only did we have the use of the dyno, we also secured an experienced technician, Chris Robinson, who works with Yates Racing as an engine and chassis dyno specialist. We were able to observe how these chassis dynamo-meters work and how we could use them to learn about how the engine output to the rear wheels could be enhanced.
The dyno we were using was a Dynojet Model 248, the same one used to monitor the Winston Cup cars. NASCAR began using the chassis dyno several years ago to keep track of the horsepower output of the teams to make sure no one was getting too far ahead of the other teams. A sudden jump in horsepower could indicate the use of illegal parts or procedures.
The device is also used by other sanctioning bodies to enforce horsepower limits. In those series, you are allowed to modify your engine any way you want, but are not allowed to exceed a maximum horsepower set by the rules. The officials let the teams use the chassis dyno, for a nominal fee, before they race to ensure they have not accidentally exceeded the limits of power. After the race, the top finishers must go on the dyno to make sure they are still within the power limits. That is a very simple and cost-effective way to keep the competition even, related to engine output, for any racing series.
The rear wheels rest on 48-inch weighted rollers. Sensors monitor the rate of increase or
Our goal for our chassis dyno test was to learn how these sessions are performed and to get familiar with the use of this type of machine so we might develop experiments and comparisons for short-track racing. We also wanted to do a rear differential comparison as well as play with pinion angles to see if there was any advantage there.
With this machine, we could determine both the maximum raw horsepower output of the engine measured at the rear wheels and also how much of that horsepower was used to turn the standard quick-change rear end that was fitted with standard bearings and seals. Once we tallied that data, we would then install a low friction differential that is called a Tiger rear end. This unit utilizes low friction bearings and seals and has polished gear surfaces along with some lightweight internal parts.
The first goal was to determine the significance of the reduction in parasitic loss compared to the added effort and added cost of production for the Tiger unit. We were to compare not only output horsepower numbers, but equally important, the coast-down horsepower figures that tell us how much of the raw horsepower is needed to turn the differential at various speeds.
Travis Carter, longtime Winston Cup owner, seems more interested in the front-end geometry
Measured A second goal, and one that has interested me for some time, was to experiment with various pinion angles to see how much power loss resulted from excess pinion and transmission angle. I had imagined a substantial loss due to this effect and I was about to get a lesson in mechanics. True pinion angle is the measurement of the side view angular difference between the driveshaft and the pinion, the driveshaft and the transmission output shaft, as well as the angles created from a top view alignment of the transmission and the pinion shaft.
Some cars, especially the offset chassis type of cars, have a significant misalignment of the transmission and the pinion. I have measured 1 1/2 inch of difference in alignment with the transmission output shaft being to the left (driver's view) of the pinion shaft. For a car with a 45-inch driveshaft measured from center to center of the U-joints, that is 1.91 degrees of angle at each end of the driveshaft. That alone would be the same as having 4 degrees of pinion angle if the driveshaft, transmission, and pinion all lined up.
With those goals established, we began to prepare the car. The choice of cars was a NASCAR Late Model with a 350 engine running a two-barrel carburetor. The crew consisted of Chris, the dyno driver; Gerald Williams; Gerald's son, Tim, who "drove" the car (as well as raced this particular car); and mechanic Wayne Ingram.