It'll be entirely custom. I had aluminum sheets made for my car at the Engineering Department at U of T a couple years ago. I had the ENTIRE underbody covered, and even had deflectors for the control arms and rear suspension. It really wasn't noticeable until you reached about 150km/h. In fact, I challenge any 850/_70 owner to do so. To be honest, the 850 underbody is already very well designed, and really only suffers in the rear sections.

What really got to me was that when I got to about 200km/h, the car started getting light, and there was HEAVY understeer. But when I had the underbody with diffusers put on, at 200km/h, the car was more stable then it was at 150km/h without the underbody work. In fact, I got the car past the 260km/h mark with the power mods, suspension mods, and underbody work. Honestly, once you get up to the 200km/h area, you REALLY feel it. It's as if the car is simply just slicing through the air.

Total cost of materials was about $75 Canadian, and took about 2-3 hours to make and install with proper cutting tools, bending machine and a lift. About the only negative side to the mod was decreased accessibility to things like oil filter, drain plug, etc. Also, due to the way I attached it, it wasn't practical to remove it every time I needed an oil change. Yes, I could've added holes added in key places, but that really would've ruined it because the air would literally get sucked into those holes, and probably ruin the decrease in cd. Also, the aluminum corroded rapidly after one winter. There was a lot of whitish powder after one salty Toronto winter. The next time I do it, I'm going to use some underbody material whereever the materal touches the underbody, and along the entire bottom. It's a great mod for someone willing to live with added work required for basic maintenance.