cracked a head at 170 k's. Its a 94 distributor ignition 3 liter in a mazda b 3000. little brother drove it for a long time and kept adding coolant. catalytic converter plugged and blew out the manifold gaskets. I changed the heads and fired it up. the bottem end was knocking and i couldn't hear it before i changed them because of the exhaust manifold gaskets gone. so I punched out the cat when i changed the motor to a junk yard motor with 80 k's . motor runs fine starts good and runs good. doesn't seem to have enough low end grunt. starts to really take at around 3 grand. was wondering if it was the catalytic converter. trying to find a junk yard cat for my truck.

 

3.0Ls dont have a lot of low end power to begin with(under 3000rpm). as far as cats go its 10 years old chop em off unless the law says other wise.