Wayne attaches a blower to...
Wayne attaches a blower to the front of the car so that air can be circulated through the radiator to cool the engine during the many runs.
We first had to install rear tires that were the same circumference as the normal right-rear tire (stagger would cause big problems on the dyno) and air them up to 40 pounds to keep wheel hop to a minimum during run-up. We also moved the front of the third link up so that there was minimum angle to eliminate any anti-squat properties. This would help us maintain the ride height while under power so the pinion angles would stay consistent throughout each run.
Once the car was positioned on the dyno and strapped down securely, we positioned the ambient air inlet in front of the air cleaner. Because we needed to eliminate the possibility of heated air coming from the headers from entering the air cleaner and carburetor, we changed that setup and removed the end of the fresh air inlet hose and the air cleaner so that the outside air dumped directly into the open carburetor.
The initial runs showed this engine was somewhat down on horsepower compared to similar engines that had been run on this dyno. The crew had suspected that for some time. The goals would not need to change because of the shortage of horsepower. Gains or losses are not dependant on the exact amount of horsepower, only percentages of loss or gain as changes are made.
The test car was a NASCAR-legal...
The test car was a NASCAR-legal Late Model type that mostly race in and around the mid-eastern portion of the U.S., including North Carolina, South Carolina, Georgia, Tennessee, and Virginia. These are perimeter-type cars with no offset in the chassis. For this reason, the driveshaft did line up nicely with only a 1/4-inch difference in alignment.
As we began the first series of runs, Tim's attempt to come up through the gears was a little rough as the car bucked on the rollers. We then repositioned the rear tie-down straps to pull down and control the vertical movement of the car rather than just pulling backwards. The take-offs were a little smoother. The goal was to get the car into Fourth gear and run it for a while to get all of the driveline parts and lubricants warmed up. Tim finally learned that if he started off in Third gear, the take-off was much smoother.
For each run-up, Tim would signal that the starting engine temperature was reached and then apply full throttle. As the lower and upper limits of rpm were reached, Chris would press a button to start and to stop recording the run. When the engine reached the maximum rpm, Tim would let off the gas, push in the clutch and quickly knock the car out of gear. The dyno recorded the horsepower as the rpm climbed and then recorded the horsepower during the coastdown, which actually showed a negative number on the chart. We were shooting to record the maximum horsepower output of the engine on run-up and then the amount of resistance at two speed intervals, 85 mph and 100 mph while the car was "coasting", stopping the "run" at around 80 mph.
There were several conditions that were out of our control and every scientific experiment requires keeping track and controlling all variables. Since we are racers and not scientists, there were admittedly some influences taking place that we could not measure or control. These were a) transmission oil temperature, b) rear end oil temperature, c) all bearing temperatures including the U-joints and wheel bearings, along with their respective lubricants, d) engine oil temperature (although we did control the water temperature which roughly correlates to the oil temperature), and e) the heating and expanding of metal parts due to elevated temperatures as each of the three-run sessions progressed.
The inlet on the left is one...
The inlet on the left is one that is used with the Winston Cup car's air cleaner box. The car's air box is turned around and fitted tightly to the fresh air supply fixture.
Chris informed us that when running a Winston Cup chassis dyno test, they monitor the rear end, transmission, and engine oil temperatures and try to keep them as consistent as possible for each run so that they are comparing apples to apples. We did not have the equipment needed to do that, so we tried to compensate by doing the three-run sessions and spacing the runs equally so that any increase in heating was consistent for each set of runs.
We were able to monitor the outside air temperature (coming into the carburetor) as well as the barometric pressure and humidity, which all stayed very constant throughout the test. Chris commented that the horsepower numbers were well within an acceptable backup percentage.
We began the test with the "old" style rear end installed with standard bearings and seals. We ran several stabilization runs to get the driver familiar with the procedure. He would take the car to Fourth gear and then hold the rpm at around 4,000 until the water temperature reached 140 degrees. Once the temperature was there, he would radio Chris and then start the run. Full throttle was then applied and Chris would hit a button that started the computerized recording of the run at 4,500 rpm. He would once again hit the button to stop the recording at 6,000 rpm. For this motor, with the small carburetor, peak horsepower was reached at around 4,800 rpm and we were interested in coast-down figures at 85 mph and 100 mph. Those speeds fit that rpm range.