Somebody put a stereo in my m1009 and probably couldn't hear it. They had sound deadening material under the hood, fiberglass stuffed in the fenders, rubber glued to the roof of the cab, extra floor mats an the IP retarded so much, it didn't clack even when cold. It was super quiet once I got it running again. There wasn't a huge power loss with the timing retarded, but MPG was down significantly. I have been been looking for more MPG and after readjusting the timing I thought drilling holes in the air cleaner as some have done to get more air in at freeway speeds would help. Drilling those holes might have helped a little at higher elevations and higher revs but the noise level has gone way up. I bought a bad civvy 6.2 for the turbo I want to install someday and it has some kind of silencer in the manifold. I wonder if it works at silencing but also robs power and MPG?
