I did a TV shoot at WGN in Chicago last month for the MCACN show and one of the cars there was the same Grumpy Vega! They fired it up during the shoot and it still sounds mean. I got to take a close look at the car and the present owner explained what all the "special" Grump stuff was on it, he was Da Man for a Chivvy head...
The funny thing about science is that if you change one miniscule parameter you change the entire outcome to the way you want it.
