everyone says that these motors are underated by GM. The horsepower figures that are put out to the public are supposed to be the lowest horsepower that the motor makes. I still know that one motor to the other can be a real big difference. I have seen two exact trucks stock, run as much as .5 seconds different between eachother. I really still believe that your breakin period is supper important to get a strong motor.

 

I have mixed feelings about this. 257 is great with only a filter. My 99 only did 218 with a filter and flowmaster mufler. It had weak tuning and a weak cam from the factory. With my LS6 cam and bolt ons, I finished with 293. I know the Fbodys are under rated by GM. It seems like the newer trucks are pretty strong.