I have to admit that vortex generators, wings, splitters, and other add-ons for aero always seemed a bit childish to me. Until I started using them. Curtis is correct that the One Lap VR4 has vortex generators. They are the stick type from EBay. I think they were $20. I followed the Mitsubishi white paper figure out how and where to install them. Here is a link to a "string-tunnel" test on a stock VR4.
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Notice the yarn in the center of the glass? Its blowing all different directions because the air is separating from the car and tumbling down the glass. Now think of a really cool wing mounted to that trunk and having it see nothing but a big ball of tumbling air? Not very efficient.
With the VG's installed I can see water just roll strait down the glass in the rain which indicates that the air is still attached to the glass as it heads down towards the trunk lid.
But nothing speaks higher about aero then our time at Daytona. In 2009 when we did Daytona with no aero Steve said the car was all over the place scary at 135mph. This year with the aero (wing, spliter, VG) Steve managed 145mph and said it was rock solid. When I went out I hit "H". If you want to know what "H" is go out and look at your speedo and see what comes after 155mph. Rock solid and it felt like I could have gone faster. I am sold on aero.
Tim