They're so cute when they're young...
Another thing that makes these shocks really special is their stainless steel pistons. Because of steel's strength, Fox can make its pistons much shorter than those made from aluminum. This is an advantage because it reduces the effects of pressure spike and some other undesirable characteristics as the piston passes bypass-tube orifices. Additionally, steel pistons expand and contract at the same rate as the steel shock body, so tolerances can be closer. Fox also uses what it calls an "energized" wear band. Underneath the piston's seal, there's a special Viton ring that puts constant pressure on the wear band to further ensure a total seal and maximum efficiency. With the special Fox fluid, the components in these shocks can perform at temperatures that would turn normal shock internals into useless mush.
For the rear of the Hemi, we went with Fox 3.5-inch shocks. The rear axle can stroke a full 14 inches of travel, so with more movement and a 1:1 motion ratio, we didn't need quite as much damping. I felt that the 4.3s out back wouldn't provide fast enough rebound. Fourteen-leaf race packs have a lot of internal friction as they slide against each other. On smaller bumps you almost don't need a shock, so you need a really loose rebound effect to prevent the rear from "packing up" - an enemy of traction. In our previous race trucks we used Fox 3.0s, which worked great. We just anticipated driving this truck a bit harder, so some more compression control was in order. During testing with the 3.5s, we found them to be superb. These shocks feature a unique "gold valve" (essentially a giant needle valve) and solid pistons, so you can externally adjust free bleed.
When we first started testing with these giant shocks, we discovered a new realm of performance. Our speed threshold opened up to new levels, literally double what we were doing before. We could mash right into bumps that would previously have had us crawling. We could now keep the truck pinned and get on top of the bumps we once called "rollers." A few days of tube tuning and spring-rate changing, and we doubled our speed again over some of the rougher sections.
It became apparent that the new limiting feature in the vehicle was the physical endurance of the codrivers. A Stock Full truck driven to the limit is no joyride: It takes a special person to sit in the right seat and get punished for hours on end. When I explained this to John Marking, head of the Fox Racing Division, he said, "Tell 'em to stop crying!"
"Sound advice," I thought.
While engineering this new truck, we took great pains to separate the ECU (motor's computer) from the TCU (transmission's computer). Normally all engine and transmission management is handled by the same computer. If something goes wrong with the transmission, a sensor then complains to the motor. Example: We start to lose Second gear in the transmission. The transmission then says to the motor, "I need to live! Give me no more than a sickly 100 hp and 2,500 rpm!"
Joe Consumer can then limp the truck to the dealer without a catastrophic failure. Conversely, Joe Racer doesn't care what his tranny "feels." He has a new transmission waiting at the next pit 50 miles away. All he cares about is winning. He wants to keep it pinned in First or Third gear at 5,600 rpm, 235 on the water temp, 220 on the tranny temp, make maximum speed to the pit and swap trannies there. That's why we used separate computers for both the tranny and the motor. The motor can't talk to the tranny and the tranny can't talk to the motor.