Before I buy the G8 GT I want to know a little bit more about the Active fuel management in the GT's V8. How does it work exactly? How long has it been in cars? Has it proven reliable? I heard it is very difficult to find somebody to repair hybrid engines, what's the story with the V8's with active fuel management? Are these engines any different from regular V8's when it comes to repair?

8 of the lifters are different. They can be turned off by an external part on the motor, which all it does is pull the fluid out of the lifter so that they no longer open the valves.

No big deal, and other then a couple parts, they are the same as the other motors.

AFM works pretty seamlessly. There are videos of G8s driving as the car goes into and out of AFM. There's occassionally a vibration that is felt under the right conditions during AFM, but I don't notice it that much. I think it was documented that the transition from 8 cyl to 4 cyl happens in 250 ms. and that there are tons of conditions that have to be met in order for it to go in (load, throttle position, etc.).

how long has AFM been around?

I believe it was put into effect on some of the GM trucks in 2005.

+ Any model year Grand Prix GXP has DoD/AFM.

I posted a long reply on another thread about AFM, including all the parameters and conditions under which it is deactivated. On my G8, I can feel a 4-cylinder vibration at lower speeds which would be essentially the same as driving a 4-banger due to half the firing frequency. Transition is completely seamless and you would never know the engine was operating under AFM control unless you read the manual. You can find out more than you want to know about AFM by asking your service department to access and print out a copy of Service Information Document ID# 1959166 which describes in detail how the whole system works.

GM actually used it back in the 80's with a cadillac. I think it was called the 4-6-8. The concept was good but it was horrible, not enough computer power. Now they are on a ton of vehicles both V-6's and V-8's. Chrysler also uses it on some of their V-8s.

I heard it is very difficult to find somebody to repair hybrid engines...
Hybrid???????

Hybrid???????

I think he was trying to say that hybrids are supposed to be hard to work on and so he's wondering if vehicles with AFM are hard to work on as well. I know it's a stretch. LOL

GM actually used it back in the 80's with a cadillac. I think it was called the 4-6-8. The concept was good but it was horrible, not enough computer power. Now they are on a ton of vehicles both V-6's and V-8's. Chrysler also uses it on some of their V-8s.

I also think/thought some of the northstar engines had it?

GM actually used it back in the 80's with a cadillac. I think it was called the 4-6-8. The concept was good but it was horrible, not enough computer power. Now they are on a ton of vehicles both V-6's and V-8's. Chrysler also uses it on some of their V-8s.

It got a bad name from the Caddy. The 6 version never worked very good and it was a repair nightmare. 4-8 makes more sense.

I also think/thought some of the northstar engines had it?

That was actually a limp home mode in the Northstar. They could supposedly run ~100 miles without coolant by rotating the firing cylinders.

Chip

05' buick raineer was the earliest i could find it on here is the short version of how it works

To provide maximum fuel economy under light load driving conditions, the engine control module (ECM) will command the displacement on demand (DoD) system to deactivate engine cylinders 1 and 7 on the left bank, and cylinders 4 and 6 on the right bank, switching to a V4 mode. The engine will operate on 8 cylinders, or V8 mode, during engine starting, engine idling, and medium to heavy throttle applications.

When commanded ON, the ECM will determine what cylinder is firing, and begin deactivation on the next closest DoD cylinder in firing order sequence. The Gen IV engine has a firing order of 1-8-7-2-6-5-4-3. If cylinder number 1 is on its combustion event when DoD is commanded ON, the next cylinder in the firing order sequence that can be deactivated is cylinder number 7. If cylinder number 5 is on its combustion event when DoD is commanded ON, then the next cylinder in the firing order sequence that can be deactivated is cylinder number 4.

Cylinder deactivation is accomplished by not allowing the intake and exhaust valves to open on the selected cylinders by using special valve lifters. The deactivation lifters contain spring loaded locking pins that connect the internal pin housing of the lifter to the outer housing. The pin housing contains the lifter plunger and pushrod seat which interfaces with the pushrod. The outer housing contacts the camshaft lobe through a roller. During V8 mode, the locking pins are pushed outward by spring force, locking the pin housing and outer housing together causing the lifter to function as a normal lifter. When V4 mode is commanded ON, the locking pins are pushed inward with engine oil pressure directed from the valve lifter oil manifold (VLOM) assembly solenoids. When the lifter pin housing is unlocked from the outer housing, the internal pin housing will remain stationary, while the outer housing will move with the profile of the camshaft lobe, which results in the valve remaining closed. One VLOM solenoid controls both the intake and exhaust valves for each deactivating cylinder. There are 2 distinct oil passages going to each DoD lifter bore, one for the hydraulic lash-adjusting feature of the lifter, and one for controlling the locking pins used for cylinder deactivation.

Although both intake and exhaust valve lifters are controlled by the same solenoid in the VLOM, the intake and exhaust valves do not become deactivated at the same time. Cylinder deactivation is timed so that the cylinder is on an intake event. During an intake event, the intake cam lobe is pushing the valve lifter upwards to open the intake valve against the force of the valve spring. The force exerted by the valve spring is acting on the side of the lifter locking pins, preventing them from moving until the intake valve has closed. When the intake valve lifter reaches the base circle of the camshaft lobe, the valve spring force is reduced, allowing the locking pins to move, deactivating the intake valve. However, when DoD is commanded ON, the exhaust valve for the deactivated cylinder is in the closed position, allowing the locking pins on the valve lifter to move immediately, and deactivate the exhaust valve.

By deactivating the exhaust valve first, this allows the capture of a burnt air/fuel charge or exhaust gas charge in the combustion chamber. The capture of exhaust gases in the combustion chamber will contribute to a reduction in oil consumption, noise and vibration levels, and exhaust emissions when operating in V4 mode. During the transition from V8 to V4 mode, the fuel injectors will be turned OFF on the deactivated cylinders. The ignition system secondary voltage or spark is still present across the spark plug electrodes on the deactivated cylinders. If all enabling conditions are met and maintained for DoD operation, the ECM calibrations will limit cylinder deactivation to a cycle time of 10 minutes in V4 mode, and then return to V8 mode for 1 minute.

Switching between V8 and V4 mode is accomplished in less than 250 milliseconds, making the transitions seamless and transparent to the vehicle operator. The 250 milliseconds includes the time for the ECM to sequence the transitions, the response time for the VLOM solenoids to energize, and the time for the DoD valve lifters to deactivate, all within 2 revolutions of the engine crankshaft.

The 5.3L V8 in my 08 GP GXP has the AFM feature, and it is pretty seamless when it activates. There's a very slight vibration that I feel in the accelerator that I've noticed, but my passengers all have told me they can't tell when it activates. The engine revs also drop slightly when AFM engages, it's usually about a 200 RPM drop at 55 MPH - from about 1700 to about 1500 RPM at that speed.

The instant read fuel economy in the DIC also skyrockets from about 20-ish MPG to well over 30, though I have no idea how accurate the instant read MPG figures are.

It sounds as if the lifter absorbs the lift to keep the valve closed and makes me ask how much lift the cam could have and this still work? Also wonder if they would hold up with a wild cam? I'm sure all will be answered as soon as the mod wars begin. The MPG with the G8 is no better than the GTO that runs on all 8 all the time so why have all these parts to worry about.

I read that there is no visual indicator of AFM on the dash. That's a shame since it would be an interesting thing to watch and adjust driving to make it kick in.

I read that there is no visual indicator of AFM on the dash. That's a shame since it would be an interesting thing to watch and adjust driving to make it kick in.
Actually, as previously posted, by starting the car while holding down the "enter" button on the left side of steering wheel you can scroll to fuel Mgt...."All active/Half active". Be careful to avoid solid objects such as trees while you watch your DIC. :p

I read that there is no visual indicator of AFM on the dash. That's a shame since it would be an interesting thing to watch and adjust driving to make it kick in.

If you're looking to optimize your gas consumption, use the Cruise Control as much as possible.

Be careful to avoid solid objects such as trees while you watch your DIC. :p

There's laws about doing that in public you know...

There's laws about doing that in public you know...

:D It's only illegal if you get caught...

GM actually used it back in the 80's with a cadillac. I think it was called the 4-6-8. The concept was good but it was horrible, not enough computer power. Now they are on a ton of vehicles both V-6's and V-8's. Chrysler also uses it on some of their V-8s.

The problem with the 8-6-4 was its engagement system. Most of it was mechanical and it did it all at once, and if things didn't line up properly, things got jammed up. It is amazing how well it worked when it did, despite no powerful computers.

AFM doesn't just happen at once; With the computers knowing exactly where each cylinder's combustion cycle is, it disables the cylinders one at a time, at the right time, and it doesn't jam up.

It sounds as if the lifter absorbs the lift to keep the valve closed and makes me ask how much lift the cam could have and this still work? Also wonder if they would hold up with a wild cam? I'm sure all will be answered as soon as the mod wars begin. The MPG with the G8 is no better than the GTO that runs on all 8 all the time so why have all these parts to worry about.

GM has said up to .590 lift is safe. There has been nothing said about ramp rates.

Actually, the G8 gets 1MPG better on highway compared to the M6 GTO using all 2008 calculations. And the G8 gets 1MPG better city and 5MPG better highway compared to the A4 GTO using 2008 calculations. Not to bad for a slightly larger car.

Chip

I think DOD/AFM is great and I bet we are going to start seeing it on more and more cars. I think there are some V6's already that are starting to do the same thing?

If I remember correctly, some company came up with a large motor that could go from 16 cylinder to 12, 8, 6, or 4... or something like that... maybe it was GM or Chrysler?

I think DOD/AFM is great and I bet we are going to start seeing it on more and more cars. I think there are some V6's already that are starting to do the same thing?

If I remember correctly, some company came up with a large motor that could go from 16 cylinder to 12, 8, 6, or 4... or something like that... maybe it was GM or Chrysler?

There's the Cadillac Sixteen concept vehicle. I think it only went down to 8 cylinders with AFM.

The MPG with the G8 is no better than the GTO that runs on all 8 all the time so why have all these parts to worry about.


Remember they revamped the fuel mileage testing method for 2008 and all the results got lower, so its hard to compare the cars based on the published numbers. For comparison the GP GXP dropped 2mpg in both highway and city ratings from the 2007 numbers.

Edit: Well I was wrong because it seems you can compare the two cars. Here is a link (http://www.fueleconomy.gov/feg/calculatorCompareSideBySide.jsp?column=1&id=21855) to the rating for the GTO if it was rated using the new standard. So the G8 gets 5mpg better on the highway cycle than the AT GTO and 1mpg better than the M6 GTO. I would say that the AFM is doing a pretty good job.

Remember they revamped the fuel mileage testing method for 2008 and all the results got lower, so its hard to compare the cars based on the published numbers. For comparison the GP GXP dropped 2mpg in both highway and city ratings from the 2007 numbers.

Edit: Well I was wrong because it seems you can compare the two cars. Here is a link (http://www.fueleconomy.gov/feg/calculatorCompareSideBySide.jsp?column=1&id=21855) to the rating for the GTO if it was rated using the new standard. So the G8 gets 5mpg better on the highway cycle than the AT GTO and 1mpg better than the M6 GTO. I would say that the AFM is doing a pretty good job.

I understand that it works and even 1 mpg at todays prices is a big thing but only time will tell if the reliability or possible problems are worth the gain. This all depends on how it is driven since the GTO owners may be a little harder on the parts it may never be an issue for normal driving. I think with a high lift cam and high RPMs it could be a problem.

My dad told me that GM had a version of AFM back in the 50's or 60's. Does anyone know if my dad is correct?

I bet all those Honda owners believe Honda invented AFM. They Honda/Toyota invented everything like overhead cam, etc.

If you're looking to optimize your gas consumption, use the Cruise Control as much as possible.

I will take issue with that under most circumstances. The cruise control is a "dumb" computer that must react to engine loads to maintain constant vehicle speed. A cruise control is fine on level ground, but it cannot anticipate upcoming loads. When you approach a hill, the car begins to slow, the engine either lugs or the transmission downshifts 6 to 5 (for example) and then the computer has to react. As a driver, you can see the "load" up ahead and begin to add power slightly as you approach the hill. This allows a "running start", and you can also begin to back off before the top, and choose to feather the throttle a bit more when climbing the hill.

The idea is to minimize throttle variations under changing loads. You want to act, not react. The cruise control is always reacting and will slightly overcompensate in hilly driving. The proof of this is to ride a bicycle in the hills. You get a running start rather than wait for the hill to slow you down before you shift and increase power. I know modern computers are quick, but they can't (yet) anticipate as well as you can. You can also watch the instantaneous fuel demand (DIC engineering mode) and see how much better you can maintain higher fuel numbers than the car does with the cruise on.

Very well put bluegoat

^ Yep that is how I drive without cruise control... plus if you can see people slowing down ahead just let it coast, no need to hit the brakes first.

Only time I use CC is if im driving a lot and need to give my foot a rest...

My dad told me that GM had a version of AFM back in the 50's or 60's. Does anyone know if my dad is correct?
Yeah, it was called "not tuning up your car every 5,000 miles results in only 1/2 the cylinders firing." :D

So the question is what real world MPG would I get driving 20% city and 80% highway? Will I get the 24 MPG estimated or quite a bit less? With all the miles I drive I can't afford to get much less than 24. My 3.8L Grand Prix really gets an amazing 26-28 MPG on the highway.

I have a feeling that the 24MPGs listed on the sticker are very feasible.

With the new standards introduced for measuring MPGs the figures are much more representative of actual fuel consumption.

But of course, YMMV.

I have yet to hit the magical 24 mpg barrier. I do a lot of Interstate driving, and 23 is the best I've done.

My dad told me that GM had a version of AFM back in the 50's or 60's. Does anyone know if my dad is correct?
Not sure about 50s & 60s, but definitely in 80s Caddys.
http://www.time.com/time/specials/2007/article/0,28804,1658545_1658533_1658524,00.html

I read or saw a review online that AFM deactivates at 70mph. Any truth to this?

I ran my car from DFW Texas to Houston over the weekend...cruise set at 75 and was monitoring AFM via Engineering mode...AFM was active at 75 on my car.

by the way, I hate AFM. it is really pointless. with the smallest incline in the highway, afm would kick off and on. I got 25 mpgs on the way to houston and 24 on the way back. all i have learned from AFM is that it makes certain engine improvements (most notably camshaft) cost more.

I wonder if any of the tuners are able to tune a higher threshold for keeping AFM turned ON? In those cases of a small incline, if you stayed in 4 cyl mode a little longer, would that help with the mileage....or has the on/off parameter already been optimized at the factory for MAX mileage?

my guess is factory optimization. i would think the factory would want the best possible mpg numbers on the window sticker.

I think 4 cylinders are going to strain pulling 4000+lbs uphill against wind resistance. Or maybe it has something to do with physical restraints and the motor might damage itself at higher revs and load???

Just talking out my A

you could get a magnacharger (mp1900) and get 26mpg AND 458HP (TO THE WHEELS)!!!!

I remember when I was kid 16 working at a filling station back in the early seventies some clown came in with a 1965 GTO that sounded like it was missing like crazy, the guy asked me to check the oil and when I raised the hood I notice half the spark plug wires were unplugged, so I simply plugged them back into the spark plugs thinking I just did the old man driving a huge favor and closed the hood and walked back up to the customer and told him what I did expecting to get a big tip> well, the guy yelled at me, jumped out of the car and unplugged the plugs again slammed the hood down and told me it was his inventive way of getting better mpg and chugged away in his bright red sputtering GTO. I guess that guy was ahead of his time, lol.

the engine use Half active at idle? I went ot engineering mode and sat in the driveway and the Management never left All Active

???

the engine use Half active at idle? I went ot engineering mode and sat in the driveway and the Management never left All Active

???

No way, AFM does not kick in at idle, only when the car is up to speed and under light throttle conditions. If you drive it in engineering mode you will see it saying half active sometimes.

WTF is "engineering mode"???

It does not shut off Cylinders, it shut off fuel to the intended cylinder and opens an exhaust valve to decrease pumping loss. and yes Caddy first tried it back in the 50-60's and called it the 8-6-4 But they I think were shutting down cylinder banks in stead of fuel systems. Please chime in I would like to know more about the 8-6-4 if anyones knowes more. Great thread. good info.

WTF is "engineering mode"???

When starting the car, hold down the left scroll wheel (Enter button) at the same time you turn the ignition key.

You'll then have "Engineering Mode" on the information screen, which will show a whole series of data readouts from fluid temps to AFM being active or inactive;)

It does not shut off Cylinders, it shut off fuel to the intended cylinder and opens an exhaust valve to decrease pumping loss. and yes Caddy first tried it back in the 50-60's and called it the 8-6-4 But they I think were shutting down cylinder banks in stead of fuel systems. Please chime in I would like to know more about the 8-6-4 if anyones knowes more. Great thread. good info.

Here's some more info :

http://en.wikipedia.org/wiki/Cadillac_V8_engine#368_and_V8-6-4

It was an all-electronic system using a solenoid mounted to each rocker and an electronic control system - as opposed to the electronically-controlled hydraulic system that's in the G8.

It's no wonder it was doomed to fail. The most powerful CPU available in 1980 was the Motorola 68000 - and it would have been way too expensive to be used as a simple engine controller. Even with the 68000, the entire system probably wouldn't have been fast enough to react.

It's crazy to think that the mobile phone you're carrying in your pocket is orders of magnitude more powerful than the room-sized IBM System/370 of 1980.

The AFM in my car is horrible. Anytime I am cruising at a set speed belkow 1600 rpm, the vibration from the AFM is enough to make me have to switch to manual mode just to get rid of it. I am bringing it back to the shop again. I like to play with the manual shifting sometimes, but I don't like that I have to use it to cover up a terrible vibration from my engine.

The AFM in my car is horrible. Anytime I am cruising at a set speed belkow 1600 rpm, the vibration from the AFM is enough to make me have to switch to manual mode just to get rid of it. I am bringing it back to the shop again. I like to play with the manual shifting sometimes, but I don't like that I have to use it to cover up a terrible vibration from my engine.

Do you have the stock exhaust system? If you do not have an aftermarket exhaust - I would take it to the dealer. I do not feel or hear anything in my car when AFM switches on (I have all stock exhaust).

All stock. It is going in tomorrow. I'm telling them that it must be corrected or I won't take it back. Wheather that means some kind of tune, module or engine, it has to get fixed. It's terrible.

I think 4 cylinders are going to strain pulling 4000+lbs uphill against wind resistance. Or maybe it has something to do with physical restraints and the motor might damage itself at higher revs and load???

Just talking out my A

thats what i thought

The AFM in my car is horrible. Anytime I am cruising at a set speed belkow 1600 rpm, the vibration from the AFM is enough to make me have to switch to manual mode just to get rid of it. I am bringing it back to the shop again. I like to play with the manual shifting sometimes, but I don't like that I have to use it to cover up a terrible vibration from my engine.

I do the same thing - let us know if you are successful.

Do you have the stock exhaust system? If you do not have an aftermarket exhaust - I would take it to the dealer. I do not feel or hear anything in my car when AFM switches on (I have all stock exhaust).

Check out the following post - the vibration is common

Any AFM deactivation issues? (http://www.g8board.com/forums/showthread.php?t=15005&highlight=vibration)

Got my car back and their answer was Pontiac told them not to do anything and that it was "normal" for the vibration. F them. I bought a Superchip Cortex today and will install and deactivate that POS AFM. Got to love a 34k list price car that vibrates like crap. Wish I had kept my Comp G.

Just programmed with my new Cortex tuner, and I am a happy boy. Disabled that piece of s#%t AFM and she now pulls like a beast. I tuned it to 91 octane since that is what was in the tank. Damn, she chirps going into second and will throw your head back. Goodbye AFM, hopoe you rot in hell.

tell us how you really feel mike, lol

Time to try decaffinated.

Just programmed with my new Cortex tuner, and I am a happy boy. Disabled that piece of s#%t AFM and she now pulls like a beast. I tuned it to 91 octane since that is what was in the tank. Damn, she chirps going into second and will throw your head back. Goodbye AFM, hopoe you rot in hell.Amen on that AFM being disabled by using the Superchips Cortex Tuner, as I did the same thing and love the performance with mine, plus no more vibration from the AFM at all now. BTW, mine Barks the tires good from the 1st to 2nd gear shift, but it also Chirps the tires when going from 2nd into 3rd gear with just 75% on the Shifts.

tell us how you really feel mike, lol

LMFAO. I dont think he liked the AFM feature!! Thats one of the first things I tuned out was AFM. Because with mine having everything Kooks, it drones and vibrates enough. But I'm not complaining because its now loud like I wanted. A little drone or vibration is fine with me for what I wanted.

I'm sorry if I gave off the impression I hated the AFM in my car, I by no means meant to come accross as a hater. Oh wait, I did.

I am soooo frikin' happy having it turned off. So I lose a mpg, but now the car acts like she should. I too bark going into 2nd and chirp in 3rd with everything turned up. I backed down to 50% TM and it is perfect for me. By far the best thing I could have done.

By the way I love the "Here Hemi..Hemi..." window sticker Jaxredge8. That is great. I may need to steal that line someday.

with gasoline above $4 per gal for 87 (and much more for 93)... Is there anyway to force the 4-cylinder mode with a tuner or other device? My commute is heavy stop lights and slow driving to the next light... improving from the 8-12mpg i get would be great.

with gasoline above $4 per gal for 87 (and much more for 93)... Is there anyway to force the 4-cylinder mode with a tuner or other device? My commute is heavy stop lights and slow driving to the next light... improving from the 8-12mpg i get would be great.

The only option you have on your car is to either Enable the AFM/DOD or Disable this feature with an Aftermarket Programmer like Superchips Cortex or Diablo Predator Tuners. As for turning it on for 4 cylinders running fulltime, that is not an option.

Hope this helps, as I have been running 87 octane in my car now for the past 2 months, and with 87 octane appoaching $4 a gallon, I am strongly thinking about Enabling my AFM/DOD to save on my rising fuel cost!

You guys might be in the wrong car if the fuel is your primary concern... AFM only really helps on the highway. During stop and go city driving the best thing you can do is improve your driving habbits. Don't mash the throttle and try to coast to stop signs/stoplights.

You guys might be in the wrong car if the fuel is your primary concern... AFM only really helps on the highway. During stop and go city driving the best thing you can do is improve your driving habbits. Don't mash the throttle and try to coast to stop signs/stoplights.

I know for a fact that I am in the right car, as before I reprogrammed my GT running the 93 octane Superchips tune, my car was giving me between 16 to 17 mpg in town, taking it easy.

With my reprogramming it and installing my Superchips 87 octane tune I am getting between 18 to 19.5 mpg in town. I think that is great for stop and go driving in town without using the AFM/DOD!

That is fantastic mileage for stop and go traffic, especially for a 6 liter engine constantly running in 8 cylinder mode. I didn't mean to sound brash, just sort of thinking out loud. When I purchased mine, I knew gas would go over $5/gallon and realized that the pluses outweighed that concern. If you're tinkering with the tune and putting lower grade gasoline just to improve gas mileage, you would be better off getting a more fuel efficient car. Again, not saying you can't get decent gas mileage, just a shame to put the focus on doing so with this car, because it was built for performance, not gas saving. Having said that, plenty of members here have averaged great numbers, without even a tune.

For example, my mom drives a 2007 CR-V. Combined (does about 70-30 city/hwy) she gets 21 MPG (she's a solid, defensive driver) I on the other hand, got 19.1 combined over a 300 mile stretch with the same split, while also getting on her a bit. Bone stock car, just decent driving habits, no throttle mashing, no hard braking and so on. It can be done, although a tune helps a lot since these cars are tuned so freaking fuel rich from the factory...

I honestly don't think a 4 cylinder is the way to go. A couple of guys from work were doing a 5 day rotation on new cars and the best they could get out of a cruise, traverse, impala and regal was around 26 mpg. Those all had either 4 or 6 cylinders. I told them that I can get that in my G8 with a 6.0 and they were shocked. If you do mostly city driving, then I can see it, but if you are commuting on the highway a 4 cylinder just doesn't cut it if you like to go over 60mph. My brother's 01 SS Camaro gets around 28 on the highway if you don't get on it (and that car is 10 years old). I don't see why they keep putting smaller engines in cars just to get 20 mpg. Just my 2 cents.

Agreed. It has to be a compromise about what works for you. I decided that I could stomach losing 5 mpg combined in order to have a car with a bad ass engine, that looks great (and unlike anything out there currently) and has fantastic value for the money. On the flip side, a buddy of mine has a Mazda 6 with about 44,000 on the odo and he claims he can pull about 350 miles with about 90% city driving on one tank of gas. I've driven his car and it is lifeless, freaking cramped (I'm 6'4" and HAVE to be comfortable while driving) and just boring to drive. Everybody is different. I meant no offense to the guy I directed my comments to. Just common sense to me that if your main worry is gas consumption and prices (which we KNEW were going to rise) you probably shouldn't get a 6 liter V8 and then worry about pushing every last mile with a tune and lower octane. These cars were meant to be woken up not put to sleep. Although like I mentioned before, a tune goes a long way to improving MPG over stock.

I honestly don't think a 4 cylinder is the way to go. A couple of guys from work were doing a 5 day rotation on new cars and the best they could get out of a cruise, traverse, impala and regal was around 26 mpg. Those all had either 4 or 6 cylinders. I told them that I can get that in my G8 with a 6.0 and they were shocked. If you do mostly city driving, then I can see it, but if you are commuting on the highway a 4 cylinder just doesn't cut it if you like to go over 60mph. My brother's 01 SS Camaro gets around 28 on the highway if you don't get on it (and that car is 10 years old). I don't see why they keep putting smaller engines in cars just to get 20 mpg. Just my 2 cents.

Because the new 4 cyl are getting 35 - 45 MPG on the hwy... but they are also way lighter.

AFM only really helps on the highway.

Maybe for some but not for me. 11 to 12 mpg city without AFM.

15 to 17 city with DOD enabled dependent upon driving style.

Huge difference.