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RACER.com Diary 8: Quenching the Thirst

I mentioned a few entries ago that the updated Challenger II is using dry block engines that don’t require radiators or a water system. All the necessary cooling is provided by the large amount of fuel being fed to the engines. We estimate a consumption rate of approximately 20 gallons per minute, which works out to about 0.083 miles per gallon. The Brown & Miller fuel line is constructed out of braided stainless steel and has an unusually large diameter at 1.25 inches. It snakes through the streamliner’s superstructure in order to feed both engines. 

Our fuel system utilizes four injectors per cylinder. One of the four is only used to start and warm the engines. A simple two gallon gravity tank sits on top of the body work and feeds pure methanol through the system while the beast gets up to temperature. When it’s suitably hot, Frank Hanerhan will radio me to turn on the internal pumps and we’ll switch over to the onboard nitro blend. 

Given the car’s profile, the actual process of fuel injection is a real challenge. I sit in a semi-reclined position and look through a 7 inch curved windscreen. There’s almost 13 feet of body work in front of me, so keeping the manifolds and injectors low is essential. The intake manifold is only 5.875 inches above the top of block, and the throttle body is actually situated in front of it rather than in the apex position. All of this is duplicated in the rear engine for the sake of consistency. If something goes wrong, we don’t want to have to think about how to fix it. 

All of this is being handled by the extremely talented Jerry Darien, who’s somehow managed to design a system that meets our extremely compact packaging requirements. How he’s managed to fit in the barrel valves, metering blocks, return lines, bypass systems and all the other component infrastructure is a little bit mind boggling to me. 

Now, here’s the money question. If the engines are cooled by fuel, what happens to them if I let up on the gas pedal during the run? The simple answer is that they’ll probably blow up. There’s not really much room for compromise with this setup, so if I feel like something is going wrong, there is a good chance that I’ll cut the engines immediately. Finger’s crossed! 

Thanks for following along. See you next week.

RACER.com Diary 7: Engineering Agony

The Challenger II was built in five months. I’ve been working on it full time for almost two years, and it’s the hardest thing I’ve ever done. The problem, I suspect, is that my dad hired a team of geniuses to design it, and another team of geniuses to build it. I’m just a race car driver that likes to weld. The engineering and packaging complexity is so omnipresent that a 1969 magazine article called it “on par with a lunar module.” Most days, that feels about right. 

When we run into problems, they don’t occur, they cascade. I’ve already had a couple of smart guys give-up on the project because of the difficulty. Very high speed racing is such an esoteric undertaking that a lot of the equipment and expertise we need is outside of the automotive community. In the past six months I’ve spent more time researching material properties and manufacturing technology than I have building stuff. But I’ve learned a lot, and I’ve found a few invaluable guys to help me overcome the hurdles.

Tim Gibson is our aero engineer, and he’s been tackling the front steering, which is the most complicated aspect of the liner in terms of packaging. He has a little under 35 inches to work with, which is the width of the car. Sitting directly in the center of that space is a 12.5 inch rear end (not a front end--we have the forward engine facing backwards), which leaves him with 11.25 inches per side. In that space he has to fit a spindle with a split king pin, a brake caliper, a brake rotor, a u-joint, a wheel, and a tire. After he’s done all that, he has to make sure that there is enough space left over for 5 degrees of steering in either direction. 

After Tim figured out how to draw the front end, we had to determine how to build it and where to source the materials. We knew we needed to assemble the u-joint out of a specially heat-treated maraging steel. Unfortunately, the u-joint is made up of two splined yokes that fit together precisely. If we tried to cut the splines after the heat-treatment, the metal would be too hard. If we cut them before, the slight warping caused by the process would ruin the perfect fit. We needed something that could cut extremely hard material to very close tolerances. The answer, it turned out, was something invented in the 1940s called electrical discharge machining. I’d tell you more about it, but according to Wikipedia “it appears that the material removal mechanism in EDM is not yet well understood.” So there. 

What matters to me is that it works, and it brings us one step closer to the salt. Thanks for following along. See you next week.

RACER.com Diary 6: Mystical Bonneville

What’s so great about a dried up lake in the middle of the desert? It inspires a kind of racing that you don’t get to see anywhere else. Rank amateurs labor next to hardened veterans under the boiling sun, moving heaven and earth to wring just a few more miles per hour out of everything from electric bicycles to million dollar streamliners. It’s a mystical place, a throwback to a time that felt messy and pioneering. If you haven’t been, go. It must be experienced to be understood.

Although Bonneville holds an exalted position in my dad’s personal canon, I didn’t spend much time there as an adult. My first visit in decades took place in 2003, when I was invited to drive a restored streamliner called The Pumpkin Seed. Given my professional background, I was a little bit cocky. Get in the car, keep it straight, pull the chutes and grab a beer. That was the plan anyway. It took me about 30 seconds to realize that everything I knew about driving had to change. On the salt, going fast can be painfully slow. Quick hands and instant reactions might send you tumbling. The conditions, which can vary enormously in the particulars, are always slick. Success at Bonneville requires a certain zen, and the fastest moments of your life can feel like they are coated in molasses. 

Another aspect is scarcity. We all want what we can’t have, and the speedway offers a narrow window of accessibility. Typically stretching from August to early October, the three month span becomes the equivalent of childhood’s summer vacations. Precious, eagerly anticipated, and all too easily disrupted by life’s unavoidable obligations, time on the salt is made more meaningful by it’s brevity, and the knowledge that if you miss your shot, you might not get another chance. That was certainly the case with the Challenger II. A burst of rain and an afternoon of wind kept it out of the record books for five decades. Hopefully we’ll have a little bit more luck this time around. 

See you next week.

RACER.com Diary 5: Power to the Ground

Although the course at Bonneville is over five miles long, it’s still useful to think of it as a drag race. As the Challenger II accelerates, our return on expended power diminishes exponentially. In other words, going faster gets harder, so if our setup requires 50% of the course to achieve 50% of our maximum speed, we’re sunk. Every car builder has some version of this problem, but salt flat racing presents a few unique challenges.

Our runs take place on what is essentially a dried lake bed, and track conditions can resemble anything from hard packed snow to slush. Maintaining traction is always an issue, so we place a lot of faith in our tires. We’ll be using a 16 inch set manufactured by Mickey Thompson Tires, which is something I’m very proud of. They’ve been producing high speed salt flat tires for a number of years with great success, and most of the other cars you see on the salt will be similarly equipped. When my dad first got to Bonneville, he couldn’t find a set of tires that were resilient and consistent, so he made some. If you can’t find what you need, build what you need. That was M/T. 

The tires themselves are an experimental design rated for up to 575 mph. They are 4.5 inches wide, banded with steel wire, and extensively cross woven with nylon. The rubber coating is only 1/32 of an inch thick, and feels almost like it’s painted on. There are two reasons for that. First, expansion. As the tires close in on maximum speed, they will grow by nearly an inch. If they were caked in heavy rubber, they would grow by even more, interfering with traction. Second is heat. More rubber causes a higher temperature buildup, and a hotter tire is less reliable. 

Thanks for following along. See you next week. 

RACER.com Diary 4: Balancing the Power

How much power does it take to beat the world land speed record? When my dad ran the Challenger II in 1968, he had roughly 1800 horsepower at his disposal. The car had a supercharged 427 Ford SOHC in the rear and a second fuel injected SOHC in the front. The power output of the engines was not balanced, so he stabilized it manually by rolling his toe back and forth over a split gas pedal. 

He was forced to perform that foot-operated witchcraft because the low slung driver’s compartment meant that that there was no space for a front blower. That hasn’t changed, but we’ve decided to fuel inject both engines in the updated car in order to balance power output. We’re using dual billet aluminum Hemi dry blocks running on 50% nitromethane. They are modified versions of what you see in top fuel dragsters, and will produce roughly 2000 horsepower each. That should give us more than twice the power output of the original Challenger II. 

If you’re not familiar with dry blocks, they don’t require radiators or a water system. All of the cooling is provided by the massive amounts of fuel flowing to the engine. In our case, approximately 10 gallons of alcohol and nitro per mile. The hardest part of this project is working within the confines of the existing space, so being able to eliminate those components was a big advantage. 

Still, packaging is a major challenge. We had to fabricate a special low profile intake manifold for the front engine to maintain cockpit visibility, while moving the throttle bodies out in front over the clutch can. Then comes the fuel system, oil system and all the plumbing that goes with it. 

Jerry Darien is supervising our engine combination and is working with RC Performance on the build. The rear engine is being assembled this week, with the front engine to follow shortly. Thanks for following along. See you next week. 

RACER.com Diary 3: In the Cockpit

In my last post I mentioned our commitment to maintaining the authenticity of the Challenger II during the update. My least favorite part of that decision has been the cockpit, which started out small and has been steadily shrinking. Given the difference in girth between M/T and myself (sorry Dad) I assumed I wouldn't run into any trouble, but preserving the driver's area has become a tricky problem. 

The streamliner's original roll cage was probably adequate, but rule changes concerning minimum tubing size meant that the whole unit had to be cut out of the substructure and refabricated out of thicker material. The pivoting canopy that covers the driver's area has a maximum aerodynamic height, so the changes to the cage had to be absorbed internally. By the time I added a HANS device, I found that my head could no longer comfortably fit inside, mostly because modern helmets are about 25% larger than they were 50 years ago. 

I've modified the aluminum driver's seat with specific indentations for the rear fuel pump, and sacrificed part of the footwell to house the larger dual magnetos demanded by the new engines. This problem is exacerbated by the Challenger II's unique four-wheel-drive system, which requires the front engine to sit backward in the streamliner. By the time I added two fuel shutoff valves, two parachute buttons, two air shifters, three fire bottles and, oh yeah, the steering wheel, I started to feel all kinds of sympathy for watchmakers and the guys that design the iPhone.  

The key to the whole thing is that I have to be able to exit the streamliner by myself in under 20 seconds, preferably faster, in case of a fire. My obstacles are two canopy latches, a 7-point harness, arm restraints, a HANS device, and the tight cockpit. People laugh when they see me practicing, but I do it for the same reason I work out everyday and eat unpleasant salads. Space is tight, and I need all the room I can get. 

Thanks for following along. Next week, engines.

RACER.com Diary 2: Chute First

This week I'm going to a talk about the modifications we've made to the tail section of the streamliner. Cumulatively, they represent the largest external change to the Challenger II, so we've been approaching them cautiously. Although we've been updating the car for over a year, almost all of the changes have been beneath the hood. The body is still old school, and we want to maintain the integrity of the original while making sure that the final product is fast and safe.

The Challenger II originally deployed its parachutes by ejecting a fiberglass subsection of the rear wing with compressed gas. That would never fly under current safety regulations, so our aero man Tim Gibson devised a plan to extend the original tail section of the car to accommodate integrated parachute tubes. This has two advantages. First, it moves the car's center of pressure away from its center of gravity, which improves overall stability in adverse (windy) conditions. This is especially important to me after a tumble I took a few years ago while we were running the world's fastest Ford Mustang. Second, the larger undertray will take advantage of the air moving beneath the streamliner to increase net downforce without a significant increase in drag. That's a rare win-win.

The reason we've been able to accomplish this without dramatically changing the exterior of the car comes down to improvements in parachute technology. In 1968, the Challenger II required chutes with 12ft blossoms. Today, we can get identical stopping power with 4ft chutes. We've performed an extensive retrofit to support the additional tail length – approximately three feet – which has involved a new substructure, as well as more mundane things like new cable mounts and brackets. We've also added a fixed Replay XD camera, which will allow us to visually monitor parachute deployment.

Next week we'll take about body shape and how we're blending it with the bottom of the streamliner. Thanks for following along!