Tilting the camera can be a nice trick, but you should then try to put the pics straight or anyway less tilted afterward (PS or whatever). aren't they a bit too tilted like they are? I often use the same technique every now and then but usually I straighten then a little bit or completely while I edit them
BTW, an IMPORTANT detail when we talk about fast cars. you need good lenses, period: i tried to shoot "quick" cars with my EF 70-300 mm F4.5/5.6 IS and although quite quick for a not-L lense, the difference there is with any of the L I tested is AMAZING and definitely on track you need a very quick lenses at that because "cheap" ones will always be a bit late, or most of the time anyway.