To get a crash with massive air you need to go onto Dayonta with 2 VERY fast cars. I did it with a freind with the 2 Zondas on arcade mode. All you have to do is get your freind to go round the track in the wrong direction at the top edge of the track and if you ram the wall and time it perfectly, you will get a bit of air your freind should hit you and act as a 200mph ramp!
If you do time it perfectly you can get about as high as the top of the flood lights... Try it, it's not too hard to do.
