In preparation for Superlap Battle, I decided to install polycarbonate windows on my 2006 Subaru STi. I had seen some pre-shaped products that supposedly seal right in, but I did not want to pay the premium. I figured I would try to make my own since I made my own splitter and had seen the savings on using raw materials (not to mention replacement cost) vs pre-made solutions. Not a knock against them, I just don’t like to pay a premium for wear items. At this point, it seems like everything is a wear item.
Step 1 Lexan
I purchased my Lexan Margard material at the Plastic Depot in Burbank. It cost me around $330. Purchasing just the rear windshield from Plastics4Performance would have run me $600+. GTA rules require the rear windshield and the rear door panels have some kind of window; so, my plan was to simply bolt the plastic where windows should go. Many folks are able to accomplish a pretty clean install of Lexan, but I had ripped all the weather stripping out of my car. This means the install would be ugly but functional just like the rest of my car. Also, we wound up doing the install 5 days before SLB; so, the cuts and aesthetics will get cleaned up later on. Most folks wind up painting the edges to hid the imperfections. I might try some oversized rubber liner.
Step 2 Measure Twice
I had the polycarbonate cut to three pieces of 5×3, 3×2 and 3×2. The 3×2 was barely enough to cover the front to back of the rear pillars, but we made it work. We removed a lot of material from the 5×3, but I don’t think it would be worth getting a smaller piece.
Step 3 Cut A Thousand Times
We wound using a jigsaw with a polycarbonate blade to trim the poly down little by little. Having an overlay would have been a lot easier, but we did not have anything handy to capture the curves. We started by tracing the inside of the top and then trimming it down to fit the curved contour along the top. There was a lot of back and forth between the car and the cutting table until we got the top to bottom to fit. Then we worked the sides out until they could bend into the grooves. We had the trunk off, which probably helped. Once we had the up/down, left/right in, we trimmed up the bottom to a reasonable fitment. You can save a lot of time by using the overlay from one side window to cut out the shape of the other side window. Be mindful of shape when bending the poly. This is really a two man job. The Lexan Margard material actually bent quite well to fit the rear window, and we were pleasantly surprised with the result — assuming it doesn’t rip out at 160 MPH.
Step 4 Drill and Rivnuts
With an eye towards replacing, removing or servicing the areas affected, I chose to use rivnuts and bolts to secure the polycarbonate. It’s a cheap and easy to use method. Drilling holes was the hardest part. For the B pillar, we wound up tapping threads into the steel underneath. We also wound up using a lock nut on a longer bolt to secure the upper rear corner of the side windows. It looks a little funny, but it beats having the window flopping around at speed. Again, be mindful of the shape when bending bolted down as you select your drill holes. I think if I add some rubber to the doors, they will actually seal up fairly well. Since my doors are gutted, I did not have to worry as much about trimming the bottoms of the side windows.
Now I just need to get my Radium Fuel Cell Surge Tank and fire suppression installed before Superlap Battle this week. If anyone wants to send me a large sheet of paper or something in the future, I’d be happy to trace my windows out for you to use as a starting point.