Years ago I also wanted to record my Cobra's sound. The exhaust side pipes that came with my kit,in a word,.....sucked. with a friend of mine we created the "Gilmore Kit" for Cobras, Vetts etc. Highly polished 304 stainless with no muffler, to blow out or the welded tabs to break loose and rattle. Inside are louvers. Louder than some would like, but alot of Cobras owners like it too.
I bought a hard drive camcorder to record my wife and I's cruise in Alaska and to record the build of my aluminum side oiler engine. Got the trip then sent it to my engine builder, which he then store but, not before I did get some driving in and record my 428 FE for the buyer.
I made a cool camera mount out of a Mickey Thompson aluminum connecting rod, to clamp onto my roll bar, but could not find it the day I wanted to record the drive. (of course)
So, I held it while driving, except when I laid it down on the passanger seat like you did.
Video #7 is when I got on the gas a bit, (crank up the volume)the others are idleing, and crusing down the highway. My Sony camcorder worked great as there was little of air noise into the mic. It came with 3 different mics for different purposie's. These vids were just with the built in, but wanted to try the other's, never got to it.
Click on this link, then click on video's to see all 11 to chose from.
https://www.youtube.com/user/427HISS