Yea, ALL of the 06-07 SS Monte's came with the active fuel management. I doubt you will get 28 MPG ever, maybe you could possibly get that if you set cruise at 55 MPH and it was in 4 cyl mode the whole time. Anytime you are into the gas even a little bit, all 8 cyl's are working, and sucking down fuel. I would not expect anything more that LOW 20's for fuel economy.

And the 4cyl to 8cyl is totally automatic, you have no control over it.

 

I know there are some issues with the Active Fuel Management but I'm not sure exactly what they are. All LS4's should have it.

 

All the LS4's I think- I think there were trucks w/ 5.3's that don't have it.

Yeah- I guess it depends how you look at it. You get better gas mileage, but have more parts to possible break down. I like it.

It depends. If you do mostly city driving, it won't kick in often, if at all. It's like EGR in that its a low load thing only- not at idle, and not under heavy throttle. It is relatively seamless though- if you test drove one without being told ahead of time- you wouldn't shout 'OMG this car has active fuel management'. If you know what to look for, and when- you'll see the gas mileage go up when it comes on, and the car will feel a little different getting back on the gas right when it pops back into V8 mode.

Not yet on mine- but I'm sure if you keep the car long enough that there will be- just like any other system, its just something else to break.

No- although I do wish there was a way to. It would be cool if when you put the car in manual mode that it would stop doing it- or maybe when you turned off trac & stability control or something. I could see if you were doing an autocross or something, that the little extra delay going back to V8 mode might irritate you.

Well, you still should be prepared. City MPG, especially in tight stop/go places- is usually a lot worse than on the sticker- and there have been people report getting even 15 mpg city. Personally, I've been getting very low 20's in the city lately- but my city driving isn't as congested as some.

Highway is a little better- especially if you're on highways that are like 55 or 65 and you're going the speed limit. If you start getting up too high, it will never come on because the engine has too much load on it (I want to say once I got over 80, it wouldn't come on, maybe even a little sooner- granted that was in a little more hilly area).

I will say, it does make aftermarket exhaust sound a little funny. With my cutout open, and with a heavy load (like just on the verge of switching back to V8 mode)- it sounds like a helicopter coming in to land- the pulses are so spaced out, it sounds odd. Other than that, its just a different tone. I couldn't tell the difference in sound on stock exhaust (mainly because it was so quiet).

FWIW- I was making about the same horsepower in my basic bolt on GTP- and was getting better gas mileage. I was usually about 22-23 city, and 29-32 highway. The upside to the GTP was- as long as you were out of boost, you got pretty good gas mileage- which was pretty much all your normal driving- the car had a really long final drive, was a pretty small engine (compared to the LS4 anyways), and had low compression- so it was a lot more forgiving to beating on it a little bit, taking off a little faster- as long as you were out of boost.

With the LS4, any time you're accelerating (except doing slight speed changes once rolling)- you're in V8 mode, and its sucking the gas up like crazy. So it takes a lighter foot to get good gas mileage.