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As discussed on this forum in other posts, fuel economy is effected by a large number of factors. It looks like your car did pretty good, given car pool weight loads. Do you have any idea of your split of highway/city mileage?
 

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Even so, he noted 48.9mpg, which is off the scale of what anyone has been getting with the Auto. I'm going to guess this was all highway driving according to the DIC and every effort made to achieve the best fuel economy possible. In any case, I'm looking forward to your results. Try removing the tune afterward and running another tank of gas to quantify your results.
I agree. If a tune was that effective in gaining that kind of fuel mileage, GM engineers would have put it on the car in the first place. Call me a doubter, but I seriously do not think an automatic Cruze Eco can do better that the manual trans, no matter the tune job. Man, if it does that much for an automatic, I can get 60+ with a tune on my 6-speed!
 

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..... depending on just how lean this car really runs from the factory may mean a few things. Chevy has purposely detuned the vehicle to allow the vehicle to grow in its class. If they come out with the 2013 Cruze and it gets 46MPG, they dont have to do anything except tune the ecu a little. A manual getting 42 MPG and a Trifecta tuned Eco getting 48, isnt that much of a change. With the boost turned up, the car is going to be making much more power, which is also easier for the engine to get up to speed. So with that, I think its possible with the right tuning. Not all cars are the same from the factory. This is why the EPA gives you an average. The factory would be getting hammered advertising a car getting 50MPG when thats the theoretical max. Cars simply will not get the same gas mileage as they did in the mid 1990s and 2000s. Cars today are so much safer than cars from 10 years ago. Cars back then had no airbags, today this one has 10. 5 Star crash safety rating across the board with the exception of roll over. most didnt have ABS, traction control, or anything like that. So things have changed. With the safety standards of the mid 90s, this car would get 60MPG all the time.
I certainly am in no position from a knowledge standpoint to argue with you on the reasons for manufacturers dealing with the EPA and/or marketing as they do. However, I am not sure I understand what you imply about cars "simply not getting the same mileage as cars of th '90s and '00s". Many of those cars had airbags, which apart from weight considerations has little effect on mileage, and the same goes for brake systems and traction control etc. Those do not, IMO, appreciably affect fuel mileage. I would agree the the air quality standards imposed upon the auto manufacturers has had an effect on mileage. Some cars today with similar engine displacement get less mpgs than my old '92 subaru (@ 28-29 mpg) 2.0L. That is with an all-wheel drive system which has to weigh more than front wheel drive. I simply do not think the improved safety of the cars today has anything to do with mileage considerations for meeting the fleet average required by the EPA.

Secondly, it is well known that if you lean the mixture on any engine you can increase the fuel efficiency, but cylinder head temperatures running much higher than designed values will certaily shorten the life of the engine. I'm not trying to pick a fight here. It just seems that agressively altering the timing and fuel charge will change some things that may not be as beneficial as the increased mileage from an after-market tune.

And finally, cars today get better fuel economy mostly by reducing displacement. At some point they have to turbo these small engines to get enough torque to run the car adequately for most operators. You have to admit, 1.4L is pretty tiny, even motorcycle size displacement, attempting to push a 3000# car.
 
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