Watch this video with Will Koch from Holiday World. This kind of stuff just geeks me out. It's the sort of thing you don't see everyday and could only come from the fantastic folks at Holiday World. More after the break.
Want to dig a little deeper? First, let us define "roll". That's a rotation around the track centerline along the train's longitudinal axis; that is, an axis running from the front to back of the train. The back seat in each car is raised about an inch, and the running board is cut away (and covered with a board). That gives the back axle, which is mounted on a longitudinal pivot, more room to swing.
A two-bench PTC car (as currently running on Raven and Legend) has a four-foot wheelbase and about 3'2" from back wheel to front wheel between cars. Between cars there is plenty of flexibility because the drawheads have practically unlimited roll on a short effective wheelbase. So the roll rate is limited by the longer distance, the wheelbase of the car. On a standard car, as on the Raven or on The Legend, the rear axle can swing about three degrees in either direction. That means the maximum allowable roll rate (without lifting any wheels) is three degrees per four running feet, or more usefully, about 16" of running length per degree. That means that in order to get up to a 90-degree bank from flat track, the train needs a minimum of 120 feet of track.
The track gauge for a wood coaster is roughly 43". The rated 3-degree swing means there is normally about 1.13 inches of clearance at the running board for the wheel. Add another inch at the running board and in fact it is probably more than that because the wheel is about 4" outboard of the seat...and the available space increases from 3.0 degrees to 5.6 degrees. That increases the allowable roll rate to 5.6 degrees per four running feet, or a mere 8.6" of running length per degree of roll. That reduces the length required for a 90 degree bank to just over 64 feet. If the Gravity Guys built the Voyage assuming that the train could roll 1.4 degrees per foot instead of 0.75 degrees per foot, they could have very easily built places on the ride where the car chassis would actually hit the track. Not good news.
The modification on the Voyage train increases its performance, therefore, the train would have no problem running on the other coasters. But because the other trains don't have that mod, they might have problems running on the Voyage. I believe Gwazi was the first coaster with PTC trains to get this modification, but though it's been standard on all of the rides the Gravity Group has built. I am certain that both Voyage and Ravine Flyer II have this mod, but I don't know if CCI ever used it.