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Speed Week 2016: Changes to the Challenger 2

Economists, in case you haven’t noticed, tend to get things wrong a lot. Anticipating this, they like to end their formulations with a particular latin phrase—ceteris paribus—that basically says, “Hey, if this thing doesn’t work out, my numbers weren’t wrong, the world was wrong.” The literal translation, roughly speaking, is “all else unchanged,” and it’s actually a great way to go about building a fast race car. If you only make one change in-between runs, it’s easy to isolate the precise effects of that change. By taking this slow and steady approach, you’re able to avoid the classic mistake of fixing something that isn’t broken, and you don’t end up with the racing equivalent of New Coke. 

But here’s the thing. We’ve been rained out for two years in a row, and we’ve had a lot of extra time on our hands. So we ended up making five major changes and some other minor ones. Is this the most conservative approach? Absolutely not. But what can I say? No one has ever accused me of behaving like an economist. Here’s the rundown on what’s different for the Challenger 2 in 2016:

Clutch Package:
This was the only mandatory change. The original clutch layout didn’t allow for enough free-play travel in the candlesticks. Each run caused them to wear slightly, which eventually resulted in the blowout we experienced on our 419mph backup pass. If you’re trying to picture the problem, imagine only letting the clutch of a street car halfway out while slamming your other foot down hard on the accelerator. You’ll definitely go forward, but there’s going to be a lot of heat, and probably a burnout. We fixed the problem by repeatedly re-machining the original parts, eventually removing a total of .625 thousandths of material. This increased clearance should prevent component rub going forward. 

Gear Ratios: 
Unlike a lot of the other cars that race Bonneville, the Challenger 2 runs dry blocks. Their optimal power band is somewhere between 5300-5600rpm. Last year, when we exited the final speed trap at 424mph, our computers measured both engines at closer to 4700rpm. We’ve modified the gear ratios in order to boost this number. This should result in faster overall acceleration, which is absolutely essential on a fixed length course, because we only have so long to get up to our maximum speed. 

The Shocks:
We didn’t experience any problems with excessive lift last year, but it remains my biggest safety concern. The Challenger 2’s shocks are custom made for us by King, and we worked with them to change the rebound control to keep the front end sucked down as much as possible. This was more of a fine tune, but it also gave me a chance to add a blow-over light to the cockpit. What’s that? A potentiometer monitors the position of the shocks and tells our RacePak data systems what changes are occurring to the car in terms of ride height in real time. If that number increases past a certain threshold while the car is going over 300mph, a bright red light on the dash will start flashing, letting me know to cut the engines (and hang on). 

It’s hard to see unless you know where to look, but the Challenger 2 now has wings. Or winglets at least. We’re talking inches rather than feet. Two small front canards, one of either side of the nose, should provide additional downforce to the front of the car. For the rear, we’ve added an under tray. This will create a zone of negative pressure, helping to evacuate mixed-up air from the sides of the car. Why is that necessary? The exhaust from our headers is confusing the air flow in that area a bit more than our aerodynamicist, Tim Gibson, would like. This should address the problem. Finally, we added some reverse louvers to the bodywork in order to expel more of the internal heat generated by the engines. It was getting pretty warm in there, and we didn’t want to risk damage to the electronics. 

We increased the percentage of nitromethane in the blend being fed to the engines by 5%. That means we’re now running 80%. Vroom vroom. 

That’s where things currently stand in terms of the car as we pack up for Speed Week. There are some other changes of course, including replacement of all the decals with hand-lettered artwork from Dennis Jones. Listed below this post you’ll find the scheduled dates for the 2016 Bonneville season. We’ll share more here as we get closer, but in the meantime you can follow us on basically all forms of social media with our crew handle, thompsonlsr. 

2016 Bonneville Dates:
- SCTA Speedweek August 13-19
- USFRA World of Speed September 10-13
- Mike Cook's Shootout September 15-20
- SCTA World Finals September 27-30