Let me get this straight....LS3 vs. L99 MPG

[Gentry78]

Originally Posted by UsedTaHaveA68

You have to realize that even with AFM (which deactivates 4 cylinders in low-load situations), it only cuts fuel to those cylinders. Energy is still required to suck in a dry charge (no fuel, just air), compress it to 1/11th its original volume, let it expand, then blow it out the exhaust. It still takes quite a bit of energy to compress that dry charge. So some of the fuel that you save by not injecting it into the cylinders is used to compress the air in those dead cylinders. That's why you don't get much better mpg with it.

And the automatics have a taller (lower number) rear end than the manuals. 3.23 auto, 3.45 manual. This helps with mpg numbers.

your wrong about how afm works, it closes off the valves after the power stroke and keeps the exhaust trapped in the cylinder to act as a air spring to push the piston back down so not that much energy is wasted(if any at low load). for example take a bike tire pump put your finger over the hole and press down on the handle then let go of the handle and watch the handle shoot back up.

[my2010camaross]

Originally Posted by JMAN311

Right, but taking away 1/2 the cylinders at low rpm cruising speeds and 26hp seems like alot just to squeeze out a 2mpg difference. It must have put it in the gas guzzler tax range without the AFM like Kyle2K was thinking. There wouldn't have been any other reason to use it IMO.



No it's not that hard to figure that the mpg between an LS3 Corvette manual would be close to the LS3 Camaro manual. But that's not what I'm talking about. The info I was talking about was the need for them using AFM at all on the auto in the Camaro.

because if it did not have the afm, it would not be rated as high as it is. very rarely do you see an auto with better fuel economy than a standard. really just the vehicles that offer this feature. Sorry about my first response.
I m really just happy to see the ratings, because initially I opted for the auto just because of the fuel economy, however after doing very minimal research I new that the ls3 would be an almost comparison to the rated mpg that they were giving the auto.
ordered black 1ss stick with sunroof
october 20, 2008

[CSK001]

If you really want to know more on this, I would suggest you to navigate about this on internet. In fact, you can have more knowledge than you've at present.

CSK

[Silver Streak]

Originally Posted by CSK001

If you really want to know more on this, I would suggest you to navigate about this on internet. In fact, you can have more knowledge than you've at present.

CSK

[DGthe3]

Active fuel management increased the fuel economy of the SS auto by around 10% compared to what it would have otherwise. A 10% increase is pretty substantial. The overall gearing on the automatic is shorter in 6th than the manual, at least on the SS's. This will cause a slight decrease in fuel economy, then couple that with the fact that its an automatic, you probably would have seen it rated at 22 or 23 mpg instead of 25. And that is rated, not actual. I would be shocked if it doesn't reach into the 30's while cruising at 55-60 mph.

[zebra]

Originally Posted by DGthe3

Active fuel management increased the fuel economy of the SS auto by around 10% compared to what it would have otherwise. A 10% increase is pretty substantial. The overall gearing on the automatic is shorter in 6th than the manual, at least on the SS's. This will cause a slight decrease in fuel economy, then couple that with the fact that its an automatic, you probably would have seen it rated at 22 or 23 mpg instead of 25. And that is rated, not actual. I would be shocked if it doesn't reach into the 30's while cruising at 55-60 mph.

Originally Posted by Silver Streak

what was so funny about that?

[GoldBowtie]

[QUOTE=JMAN311;342130]17/29 mpg (city/hwy) – 3.6L DI VVT V6 with manual transmission
18/29 mpg (city/hwy) – 3.6L DI VVT V6 with automatic transmission
16/24 mpg (city/hwy) – 6.2L V8 with manual transmission
16/25 mpg (city/hwy) – 6.2L V8 with automatic transmission



What's up with that? Guess I didn't realise how much at automatic tranny can rob fuel mileage....:QUOTE]

Auto's fuel economy is a pleasant surprise! When have you ever seen an AUTO with better economy than a six-speed manual in the same application? And apparently, based on early performance numbers, the auto is as quick to 60 as the stick --- go figure!!

[CamaroSpike23]

[QUOTE=GoldBowtie;343462]

Originally Posted by JMAN311

17/29 mpg (city/hwy) – 3.6L DI VVT V6 with manual transmission
18/29 mpg (city/hwy) – 3.6L DI VVT V6 with automatic transmission
16/24 mpg (city/hwy) – 6.2L V8 with manual transmission
16/25 mpg (city/hwy) – 6.2L V8 with automatic transmission



What's up with that? Guess I didn't realise how much at automatic tranny can rob fuel mileage....:QUOTE]

Auto's fuel economy is a pleasant surprise! When have you ever seen an AUTO with better economy than a six-speed manual in the same application? And apparently, based on early performance numbers, the auto is as quick to 60 as the stick --- go figure!!

not to mention the fact that the SS auto has more going against it than the manual.

L99 motor with less cr, different pistons, lifters, cam, more drivetrain loss thru the trans, as well as a different rear end gear ratio.

what they should test (and/or offer) is rear gearing of the M6 in the A6.

[JMAN311]

Originally Posted by DGthe3

Active fuel management increased the fuel economy of the SS auto by around 10% compared to what it would have otherwise. A 10% increase is pretty substantial. The overall gearing on the automatic is shorter in 6th than the manual, at least on the SS's. This will cause a slight decrease in fuel economy, then couple that with the fact that its an automatic, you probably would have seen it rated at 22 or 23 mpg instead of 25. And that is rated, not actual. I would be shocked if it doesn't reach into the 30's while cruising at 55-60 mph.

Do you think they would have got hit with a gas guzzler tax if the mpg rating sunk into that range of 22-23? To me that still seems like the only reason to have used AFM. Maybe I'm the only one that would have liked to see an LS3 @ 426hp with an auto at the sacrifice of only 2-3mpg.

I tried to calculate the EPA combined ratings with the formula from the gov website but couldn't get the same numbers they have on their list of 2009 cars that got hit with that tax. Maybe auto makers have different city/hwy mpg numbers for the feds than what they advertise or there are just more factors to the equation that they aren't letting us know.

[Rodrunner]

The cutoff is a "Combined MPG" of 22.5mpg. The EPA's Combined MPG is basically the average of city and highway with an adjustment. The '08 SRT-8 rated at 13-18mpg gets a "Combined MPG" of 19.1.
So if the A6 w/o AFM was rated to 21 or 22mpg highway, it still might not have gotten the tax. But it certainly is more appealing to perspective buyers at 26 highway.

[UsedTaHaveA68]

Originally Posted by Gentry78

your wrong about how afm works, it closes off the valves after the power stroke and keeps the exhaust trapped in the cylinder to act as a air spring to push the piston back down so not that much energy is wasted(if any at low load). for example take a bike tire pump put your finger over the hole and press down on the handle then let go of the handle and watch the handle shoot back up.

I stand corrected! At first I was going to say it still requires energy to compress that gas, but when I read more about it I noticed that the energy required to compress it is basically cancelled out the by energy released from the expansion of the compressed gas in the opposing de-activated cylinder. Guess I should do more research before chiming in next time

[DGthe3]

Originally Posted by JMAN311

Do you think they would have got hit with a gas guzzler tax if the mpg rating sunk into that range of 22-23? To me that still seems like the only reason to have used AFM. Maybe I'm the only one that would have liked to see an LS3 @ 426hp with an auto at the sacrifice of only 2-3mpg.

I tried to calculate the EPA combined ratings with the formula from the gov website but couldn't get the same numbers they have on their list of 2009 cars that got hit with that tax. Maybe auto makers have different city/hwy mpg numbers for the feds than what they advertise or there are just more factors to the equation that they aren't letting us know.

Yes, there are other factors besides the advertised EPA combined. I don't know what all of them are, but it is not the same. In cars that are similar to the Camaro, the rating on the GG tax is close to the highway fuel economy numbers so that is a good approximation. Which would have put an LS3 auto right on the bubble.

Anyway, in my mind the L99 is an LS3 setup for active fuel management. And the automatic is intended for more of a daily driver so the added fuel economy will be beneficial to most buyers. The extra power probably wouldn't do anything for 0-60 and might get 0.2s knocked off the 1/4 mile, I'm not a drag racer so those are purely guesses. But if true, is that worth paying an extra 10% for gasoline on a daily driver? For you maybe, the average customer probably not.

[domano 68]

Originally Posted by JMAN311

So you have a 426hp 6-spd manual tranny car getting 16/24 mpg
and an active fuel management 6-spd auto car with 26 less hp can only get 1 mpg better?!?!?!?

What's up with that? Guess I didn't realise how much at automatic tranny can rob fuel mileage....

The L99 mileage is relative to how you drive the car. Obviously the longer the AFM system is activated, the better the mileage will be. We don't know how long the AFM system was activated, nor do we know how the idividual drove the car when the EPA measurements were made. I would be willing to bet that I could get 30mpg out of a tank with an L99. You'd be surprised how much you can beat the EPA rating by if you just slow down (did I say slow down ). I've beat it by 40% in other vehicles. Interesting stuff.

[Gentry78]

Originally Posted by UsedTaHaveA68

I stand corrected! At first I was going to say it still requires energy to compress that gas, but when I read more about it I noticed that the energy required to compress it is basically cancelled out the by energy released from the expansion of the compressed gas in the opposing de-activated cylinder. Guess I should do more research before chiming in next time

don't worry it happends to the best of us