When the latest Evo model Mitsubishi Lancer came out I looked with interest at the rear fins stuck all over the trailing edge of the roof.

Mitsubishi calls them vortex generators, a term I was already familiar with from aircraft. Some aircraft use vortex generators placed on the upper surface of the wings to delay flow separation and so reduce the speed at which wing stall occurs. But the Mitsubishi isn’t an aircraft flying along, so what do they do on that car? A tech paper from Mitsubishi soon revealed that they improve the flow of air down the rear glass, so getting more air to the wing and probably also reducing the size of the wake.

I was inspired enough by the design to make a bunch of my own (using the alternative shape shown in the tech paper) and stick them over the trailing edge of the roof of my NHW10 Prius. However, on-road testing showed that the reduction in drag (for that was what I was after) wasn’t enough to make a dramatic difference to fuel economy, as I had already achieved with my frontal undertray.

So I put the idea to one side, perhaps for later revisiting with different shaped vortex generators or another car.

But when I came across a discussion group post that talked about an Australian company selling vortex generators with the aim of reducing fuel consumption, my interest was again aroused. The company, VG Fuelsavers, had recently featured on local TV as an invention worth watching. The website http://www.fuelsavers.com.au showed some pics of the vortex generators, which are made of sheet aluminium and look much more like aircraft designs than the shape of the ones used on the Evo Lancer. A kit of nine vortex generators with fitting instructions, cleaning wipes, double sided tape and a template cost AUD$110, including delivery. Which seems fine by me.

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