I kept wondering what the hell everyone was talking about when they discussed the active fuel management system on the V8. I must be older than I think because I never felt it or heard it...until now. I got my MagnaFlow system installed yesterday and OMG, the car sounds like a ricer when the AFM kicks in. How would it effect the mileage if I have Vector MotorSport turn it off when I get the FlashExpress tomorrow? Do you think I would be sorry I did that with gas over $1,000,000 a gallon?

You will probably not se much diference round town. If you keep her at 50 on a perfectly flat road you will see about a 15-20% difference.

Get a tune and defeat it completely. I'm going to do that with mine eventually.

The tune will adjust it. I have MF and its not bad with AFM. U do hear it, but I will get rid of all of it when I do cam unless I try AFM cam 1st. Charlie

I went without mufflers for an entire weekend and the AFM didn't make me cringe. Guess its just a matter of personal preference.

I went without mufflers for an entire weekend and the AFM didn't make me cringe. Guess its just a matter of personal preference.

Thats what Im saying. Most have not had AFM so it is a unusual sound, but acceptable. I guess u got to give some to get some.

To me the sound is worth the MPG gain... 3-4 MPG adds up FAST!

And as I thought about it I guess you can always turn AFM off by kicking the stick into manual mode. I think I will leave it alone when I get my tune. I didn't realize it would make that much difference in gas mileage, 15 - 20%, the way it kicks in and out all the time. Also, over time I will probably learn to drive better with it and play little games to see how long I can keep in V4 mode.

And as I thought about it I guess you can always turn AFM off by kicking the stick into manual mode. I think I will leave it alone when I get my tune. I didn't realize it would make that much difference in gas mileage, 15 - 20%, the way it kicks in and out all the time. Also, over time I will probably learn to drive better with it and play little games to see how long I can keep in V4 mode.

Two things... it will only be that much of a gain in the scenario I outlined. Under other conditions it will be all the waydown to 1-2% in city driving and 0% if you never get your foot out of it or are in stop and go traffic. Putting it in manual mode does not stop AFM. To oversimplify manual mode affects TCM functions AFM is a ECM function (tranny gear is a factor in it though... so like I said it is an oversimplification). You can reduce how much it comes on by selecting your gears to keep a jigher load on your engine, but once you get into the flats at highway speed in 6th it will kick in.

My LS2 car is returning higher overall MPG than my AFM G8. I'm not crazy about it nor am I convinced it actually saves any fuel in the real world.

My LS2 car is returning higher overall MPG than my AFM G8. I'm not crazy about it nor am I convinced it actually saves any fuel in the real world.

What is your LS2 car is the question.

What is your LS2 car is the question.

06 GTO manual. I average a consistent 17-19mpg city. I'm getting 14 in the G8 right while making less power doing the same driving. Average speed between fill ups is about 30mph.