Video: Bonneville Salt Flats, 2016 truck test run

Poor salt conditions resulted in all 2015 events being cancelled on the Bonneville Salt Flats. The salt is still very thin and is in marginal condition, but steady dry weather has resulted in a hard, dry surface and has allowed for some running on the salt again. Mike Cook organizes a Land Speed Shootout every year and in preparation of that event, he organized a test & tune session for a very limited number of vehicles. In 2014, movement in the supercharger rotors resulted in an explosion and fire that caused a fair amount of damage and restricted further testing. New shafts were built for the supercharger rotors to eliminate movement and after testing an engine on the dyno, we felt confident that the problem was solved. Our goal for this initial run of 2016 was simply to achieve full throttle in high gear and for Les to get more comfortable with driving the car.

Les has trouble hearing the engine cleanly, with considerable noise related to car speed from the rear ends, Halibrand quick change units, multiple drive belts running the drive shaft along the length of the car, wind noise, etc. Throttle position was very low and the engines weren't making enough noise for Les to be able to hear much – notice that the car is in 3rd gear before he even gets above 25% throttle opening. Also, in spite of a fairly limited windshield opening and the use of tinted glass, there is plenty of external brightness with the sun and the salt, and he has considerable problems seeing the dashboard. A second cabin light was added after this run in an attempt to brighten the dashboard, as well as a simple indicator that was taped to the screen to line up with the desired shift point on the segmented RPM graph to make it easier to judge engine speed. It's also planned to move the gear indicator lights to the top of the display to locate them as close as possible to the driver's line of vision. Also, Les is still getting accustomed to the sequential air shifter, which takes more time than is ideal to apply the next gear.

The end result of poor vision, poor hearing and the sequential shifter issues was for Les to somewhat lose his way during the early part of the run, getting fairly close to the 2 mile marker on the right side of the course. He ended up short shifting considerably due to being uncertain as to what gear he was actually in, and the shift points were much lower than would be needed if the attempt was to accelerate as quickly as possible – the engine was only running at 4800 RPM when it was shifted into high gear. In spite of running well outside of the engine's intended RPM range, acceleration rates were still strong at the end of the run, and there is clearly no problem with running much more speed than was achieved on this test run.

Full throttle was reached in high gear, although it doesn't show on the data as the throttle position sensor started to glitch towards the end of the run. The computer's GPS measurements showed a peak speed of 360 mph, achieved at an engine RPM low enough that the car should have still been in 3rd gear. The salt was a bit rough but at high speed, the car glided easily over the rough spots and it ran much smoother at 300+ mph than it did at low speeds. There is a considerable amount of bouncing before 0.2 and 0.5 miles, and after analyzing the data it was clear that this was wheel hop resulting from tire spin more so than a rough course. It's possible that this wheel hop is what caused the quick change gears to fail on the next run – the car weighs over 8000 pounds and even with such low throttle application there would still be a lot of stress in the gears.

This first attempt at reaching full throttle was "much more good than bad" but there are still problems to solve. The biggest issue is with tire growth. The tires available to us now are larger than those we had when the car's wheel covers were built, and after making a single run, they permanently deform and grow even larger. There's no longer enough room inside the wheel covers for the tire growth expected on a high speed run, so modifications need to be made. This is no minor job – the frame will have to be cut into in order to achieve the required space. Also, the parachute release mechanism on the drag chutes had been modified after the previous test resulted catching the release hook and tearing a chute panel. With the modified release we still had the same result, so a new method of releasing the chutes is now under construction. On the longer term, exhaust collectors will be built for the front engine to move the exhaust opening behind the rear engine's intake to avoid contaminating the intake air. Running plans for the immediate future will depend on construction of the new wheel covers needed to run higher speeds.

See who is running at Bonneville this year.

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