Tuner or Performance Chips - Do they work?

jfkmk wrote:

2oldman wrote:
If these mods could really do something they'd already be on there.

Perfectly said. What manufacturer wouldn't want to boast the best mileage and the best power?

Sadly that's not the case.
Manufacturers save moeny anyplace they can - yes, at the price of better performance or efficiency. Because of that, performance is often improved by replacing stock parts with better designed and more expensive after market items.
The engineering staff of an aftermarket company like Edelbrock or Banks are given a much bigger budget than the oem will and they can sell the part form far more than an oem is willing to pay.
Finally, it comes down brain power. Some aftermarket companies simply have better engineers and/or they don't burden them with the limitations I've already stated.