We played around with one on our 500" last summer. Went from a pro systems single 4 (1150 cfm) to the tunnel ram w/ 750's. The car slowed up .07 and went a full mph faster. Crazy thing is it was very friendly with starting. But, in the end its sitting on the bench. I believe the cam I'm running just wasn't right for the setup. It's always fun to see what it does though....
If it picked up 1 mph it wasn't down on power, even though it was slower. My guess is the carbs needed some tuning.
Some older tunnel rams don't have very large ports and some of the newer single 4 race intakes might be almost as good (or better) in the as cast form. Don't know what single 4 you had and what tunnel ram you tried though. One nice thing about tunnel rams: it is easier to size the ports in order to match the engine.
