I did a lot of NVH work at Ford. ANY metal-metal contact with a powertrain component will cause booming in the cabin and drive you nuts. That TKO conversion has me wondering if you've got a clearance issue in the tunnel. Maybe the trans mount is twisted or hard against a stop?
Bill, I think I am on to something concerning the annoying drumming sound in my Mustang cabin. Thanks for encouraging me to take a second look. When I completed the TKO conversion, I was careful with the clearance and fit in the tunnel area. Even with the optional cut-down case, a few well-placed hammer blows were required. Did not look that close at the trans mount area.
Today I pulled out a untried, Holley 4150 1850-2 from under the bench. It already had a fresh renew kit in it, but I have never run it on any engine. Took a couple hours to work out some bugs and install it on my 390. Anyway, the vibration and cabin sound remained at 1950 rpm - 2200 rpm range. However, this carburetor did not dribble as much at 2000 rpm.
Turned the idle up to 2000 rpm, slid under the car and held my hands on the underside of the tunnel. It was really vibrating.
While I was lying on concrete, on my back and trying not to burn myself on the exhaust, inspected the TKO transmission mount. Thought this looked suspicious
Took a break to allow the exhaust to cool, moved the Mustang to the middle of the garage and put it up on four jack stands. Removed the transmission mount and found a contact mark where the transmission case and the mount were touching. Those are not cracks in the transmission case, just casting parting lines and a scratch in the aluminum.
By now, it was time to grill some pork tenderloins, enjoy a Shiner beer and have some supper with my wife.
Tomorrow, I will get out my trusty grinder and create some clearance between the trans case and the mount.
Once again, I really appreciate everyone's input.
Clark