Hello! There is no "user friendly" method to adjusting when the Active Fuel Management switches between 4 and 8 cylinders. However, there are softwares out there, that with a laptop, will allow you to "modify" how the Powertrain Control Module operates, and from there, you can adjust many of the settings, including the requirements for switching to Economy Mode. One such software is HPTuners (www.hptuners.com) You have to purchase the software and the cable and have a laptop, but once setup, you can make many modifications.
Increasing horsepower doesn't typically increase economy. In fact, items like superchargers will increase fuel consumption. However, some items that increase horsepower, do so by making the engine more efficient, which in turn help with fuel economy. For example: ehxuast systems. Manufacturers are requried to meet certain noise levels, and therefore often have restrictive exhaust. An aftermarket exhaust system will help the engine breathe better, which frees up some horsepower and the engine runs more efficient.
You can also buy hand-help programmers that are specifically designed for improving fuel economy (hypertech and superchips are two common ones). These are basically like the HPTuners I mentioned before, only they are "pre-programmed". You can't make the changes you want, only whats in the programmer. Its less expensive and easier to do, but not as flexible.
I hope this helps, please let me know if you have additional questions!
Do you know of any instances where the HPT tuner software has been used? Will it cause damage to the drivetrain? I am currently in the Durham, NC area, do you know anyone qualified in the area who can make these adjustments?
Would you suggest using the standard Hypertech/Superchip modules? I would like to achieve at least 25 mpg at cruising speed.
I use HPTuners for my LS1 powered Trans Am. Its very good with the GM V8 engines, however you have to be familiar with modern fuel injection systems. The software is so flexible and so powerful, you can basically do whatever you want and if not carefull, it can cause damage. I don't know anybody in the Durham area, but I can ask some of the local tuners here in charlotte if they can reccomend anybody in that area.
The Hypertech/Superchips is much more user friendly than the HP Tuners and its something you can do yourself. Its pre-programmed, so you can't do damage to your vehicle. you plug it in, answer a few questions and it will swap ECM calibrations and you unplug it and drive off. If you need to have any work done at the dealer, just swap them back to factory and take it in (the dealer can void the powertrain warranty if they know the calibrations have been changed, so you need to swap it back to stock before getting service). Once done, re-install the software! Check out their websites and see what they have to offer!