You can't at all. Unless you have the DIC on that particular page (it's combined w/ instant fuel economy), you'd never know. I've tried to guess when it's on when going up a slight incline, or slowing down or some other light load situation, and have been wrong several times. There is no giveaway from the exhaust note, because at cruise, it's so subdued anyway. You can hear it at cruise, but it sounds the same. I don't know how they did it.

 

If you would like to see how the DOD works just go and drive a 2007 Tahoe and you will see how little it intrudes on your driving..it is seamless to say the least..who ever thought it up was pretty smart..

 

Well at least by bringing this up we all learned something and not having driven one I will have to live and learn. At least here when you through something out there you get answers and learn

 

http://www.popularhotrodding.com/fea...0405phr_gmdod/

"In our interview with Chris, we remembered that there was one other mid-sized utility in the GM stable, which uses a 5.3L V-8, the Buick Ranier. That vehicle is not slated for DOD, although it will have the new LH6 engine (minus DOD). Chris's explanation for the exclusion of DOD in the Buick Ranier is too long to print here, but is worth a condensed look in light of the next point we need to make. GM deemed that in order for the customer to truly buy into the concept of DOD, it must be absolutely undetectable. Even with ETC and tuned engine mounts, there was a distinct difference in exhaust tone between V-4 and V-8 operation. To mitigate this difference, a pressure-activated valve in the muffler adjusts the exhaust path to deliver an appropriate amount of noise reduction. It was found that such an exhaust system had packaging limitations that precluded its use in the Buick Ranier, which has a shorter wheelbase than the vehicles currently slated to receive DOD."

There is a valve in the muffler that is adjusted by exhaust pressure, and works well to hide the fact that there is a change at all in how many cylinders the engine is running on. It is a pretty nifty little trick GM pulled.

 

Well, now it makes sense. The valve is what keeps the sound from sounding different. I guess that is nice because if you were to put a set of flowmasters on or whatever, you will not have to worry about it sounding strange during cylinder cutoff. It will just be quiter during cutoff. Which would not be a bad thing for highway driving or whatever. But, on the otherhand, it may make its operation more noticable when your volume suddenly drops. But, I guess the only way to tell is if we could get some exhaust clips from someone with an aftermarket exhaust and AFM.

 

Quite the opposite unfortunately. If the valve is in the muffler, and you change mufflers.....

What's that going to do to the sound. Should be interesting.

 

I just hope they put a 4 barrel carb on it. I don't want to mess with that there fancy fule injiction. Probably make the whole thing unreliable and unmoddable. And maybe we can get a 14x6 wheel on bias ply option. Do you really trust them fancy radial tires? Let's keep it basic.

 

well... the exhaust companys test their sounds out before they sell it... they'll make sure it sounds good, and probably have to buy that little peice from GM, its probably a patent...

 

I've said it before and I'll say it again, there needs to be an ON/AUTO/OFF switch for AFM. I didn't realize that GM does use a valve in the exhaust to help the sound, but I suggested that a while back. Sorta like the Z06's exhaust valve.

This switch could be used as a valet switch. Switch the AFM to full time on and you will only be at half power. It's pretty obvious that the Camaro will get a 400hp motor, so wouldn't you prefer that the valet (or for parents, your teenage child!) only be able to use 200 of those ponies with the exhaust all quiet?

Also, there are times when I would prefer to get better fuel economy all the time. Who really needs 400hp on tap all the time in their daily driver? My current DD only makes 200hp and it goes through traffic just fine. Heck, like somebody else said, include this on the V6 also. Cars have been getting along just fine with less than 150hp for ages.

 

I am not sure if the car would idle at all with the AFM switched to full time on. If it would idle fine I am sure the PCM would leave it on while the car was sitting at a light, but as it stands the engine idles on all 8 cylinders, not just 4.

I wonder how much power the engine would make using only 4 cylinders? I would bet that it would make less than half of what it makes on all 8, due to the extra friction of the dead cylinders not making any power. Pumping losses would probably be higher too, due to the fact that the dead cylinders constantly keep compressing the volume of air in the cylinder over and over again, and even though the air kind of acts like a spring and helps push the piston back down, I would bet it is robbing the engine of power far more than it is returning it through that spring action.

I said it before, if the Camaro gets AFM, it wills always be on, with no defeat switch. No other vehicle GM has produced with this engine control system has had a defeat switch, and it seems unlikely any in the future will have one as well.