Then I used this contraption to draw a line 5" in front of the face of the bumper. The rules allow for 6" but I though 5" would work.
What you may find out pretty soon is that polymetal does not hold up well to abrasion. With 5" of extension, you will scrape the front of the splitter when the front dives under braking. Especially considering that you actually have about 10" of extension from the front edge to your first structural fastener. If you go fast enough, it's going to flex and bend downwards from the air pressure diff.
If you're lucky, it will merely wear the front to a razor's edge. If you're unlucky, the polymetal will crack and split. The latter is what happened to our first one, and the razor's edge is what happened to our second.
Polymetal does look gorgeous and shiny, though!
BTW, there is a maximum splitter length after which you begin to lose downforce. Splitters work by tapping into the high pressure bubble formed at the front of a car, the size of which depends on your speed and on how huge an airdam you have.
For a NASCAR stock car with a solid front air dam, a splitter length of 10cm (4 inches) was the limit before downforce started to drop.
Because the front of our cars is not a solid air dam, the high pressure bubble in front of an Elise/Exige is likely to be smaller than that of a stock car. If you aren't driving at 100mph+, the pressure bubble will be even smaller. So, it may not be a Lotus street vs performance compromise that the stock splitter is only 2". There may actually not be any benefit to running a splitter longer than that on an Exige/Elise with a stock front clam.
I'd love to get time in a wind tunnel.