Think you're on about like a 'whip' when you bring the car at nearly 90degrees to the take-off ramp, i'm not saying im an expert or owt but you do it by flicking the steering just at point of take-off to bring the rear round,then bring it back by turning the other way, then gradually back again to straighten and land you need on power too, to giroscope it back enough, all timed perfectly
. Backflips are easy, bigger tyres help, just keep the throttle on until you do about 280 degrees then let the power off, you can also do a backflip with 360degree horizontal rotation too by flicking the steering at the take-off point and keeping it locked over on the same lock and at full throttle, then easing back on the throttle at about 280 degrees again with a little opposite lock to land level. A good flick profile of the upramp makes things a lot easier.
PS: with a 4wd
Jumps are ace
you improve more when racing on tracks with tricky jumps i think than just loads of bodding on an average track.