This in kind of hard to explain, but I`ll try. I have a 406 in my 74 Z28, with th350 and 4.10 gears. This car is very very very slow. My 1/4 mile time is 15.01 at around 82 mph. I would have to think that I have major firing problems, possibly busted rings. I changed the plugs and wires, didn`t help any. Also, if you hold the pedal to the floor, the car sounds like its running out of gas for about 4 seconds, then runs for about 2, then starts running out of gas again. What do you guys think.