So I recently traded in my venerable VW TDI for a Volt. Although the ol' VW was getting 50-60mpg with plenty of mods the nickel and dime repairs were starting to take their toll. I love to tinker but spending every other weekend replacing a $15-30 dollar part was getting annoying.
Anyways on to the point of this post. I ended up buying a 2015 Volt. Upon looking under the car I was confused by the lack of an engine belly pan. I thought it might be missing but a phone call to the dealer and subsequent internet searches reviled that's just how GM did it.(or didn't) So while aero was a concern my primary reason for the engine pan was all of the random things I've accidentally hit over the years on the road and the need for some protection.
Initially while I did my research I jumped under the car and threw some coroplast with a Thermo Tec heat shield since the exhaust was practically touching the coroplast. I just used the factory small screws that also hold the factory aero in place. Nothing fancy. It measured 30in x 24in. I had a 36x24 piece of coroplast in my garage.
Once I realized that there wasn't anything missing from my car I fashioned up a more heavy duty shield. I used some aluminum diamond plate I got on sale at the local big box store. It initially measured 36in x 36in. The two frame rails that run down the car are roughly 30 inches apart. (outside to outside) GM was nice enough to leave two 3/8-16 threaded holes midway down each frame rail and I just happened to have a bunch of matching bolts! The threaded holes don't go all the way through so you'll have to check your depth, I used bolts that were 2 inches long but I also put some old scrap anti-vibration mat in between the plate and the frame as a makeshift bushing.
Up front there is a cross member between the frame rails. It isn't level with the 3/8-16 holes further back. (about 2 inches higher, reference point is the ground) It had two nice holes that also don't pass all the way through the rail but there didn't appear to be any obstructions above them if you wanted to drill them out up top. I used a rivnut tool to set M8 threads in the holes. The M8 was a touch small, I'd recommend an M10 but the next size up I had was 3/8 which was way to big. The M8s may end up working their way out of the holes in time in which case I'll set a larger rivnut or I'll just drill out the top of the hole and put a nylock nut and bolt through.
There are various holes in the two main frame rails that do pass all the way through and I considered using them before I found the 3/8-16 threaded holes. If you end up going 36 inches back from the front cross member you'll need to cut the corners off your plate as there are some mounting points for the suspension that reside back there. Also there is a bolt that hangs down in the middle that you'll need to drill a hole for back there.
In the pictures you'll see my coroplast panel. The six mounting points. The front two I used much smaller bolts but for the picture I put two really long ones in to make their location obvious. The last picture is the completed plate.
If there are any questions, I'd be glad to answer them!
