I hear a lot about these, but don't know much. From what I understand, or at least think I understand they basically reprogram your vehicles computer.
I'm hearing claims of 25-100 more HP with similar gains in torque and improved fuel mileage. All seems too good to be true. If so, why not program them that way from the factory. Seems like there have to be some downsides, but I'm hearing of lots of guys spending the money for them.
What is the true story to this? Is it worth the expense and what are the downsides?
