It's almost the same as an overdrive button. With the power button off the tranny will shift normaly going from 1st to 4th gear shifting at normal rpm points under normal driving. With the power button on shift points will be raised to something like 4k, keeping the car in the torque band, and will not shift past 3rd gear. What this does is keeps the rpms up for easier passing. No point in having if on period under normal driving conditions. The only time I end up using it is when passing going up a hill to make the tranny work a lot less. If you ever noticed if you are already in 4th cruising at freeway speeds and hit the gas to pass someone it drops into 3rd for a few seconds and then back to forth making for a slower passing rate. If you engage the power button it will drop it into thrid and keep it there until you turn it off. This is also good for the occasional freeway races where you exceed 100+ mph. You'll want to keep the power button engaged to make sure you take maximum range of thrid gear, then turn the button off so that you can get into 4th. Basicly you shouldn't have to use it except like I said passing on a hill to make it easier for the tranny so it's not shifting back and forth between thrid and forth. The only other time I could see using it is if going up hill on a curvy mountain road where you are climbing in altitude. You'll want to use the power button to again make it easier on the tranny. Does it make you any faster? NO!! I've done time trials at the track and saw no difference, it's strictly for specific cases where it's easier to keep the rpms up. It's equal to when driving a 5-speed where instead of shifting at a comfortable 2500rpm you shift at 4k rpms just so that you are in a higher rpm band for power.