I know that LSx engines get stronger as they get less "green," but I've never heard of them getting better gas mileage as well.

When I got the GTO with about 6k miles on it, I got 13.3.-13.5MPG consistently on each tank. Then one tank I averaged 14.1MPG and was presently surprised. That went on for a couple tanks, and then the last tank I got 14.6MPG. I thought maybe I was just babying it more than I used to, but now more than 3/4 of the way through the current tank I'm getting 15.1MPG and am definetly not babying it all the time.

Anyone ever heard of the LS1 increasing performance AND gas mileage over time?

This is also interesting because the Alero which is 700lbs lighter and has less than half the HP never got above 18.x MPG. So, the GTO is bigger and really isn't a whole lot worse on MPGs.

I should also add that it has all been city driving in both the GTO and Alero.

why wouldn't it get better milage as it was breaking in? if you get more power from the same rpm , should beable to use less gas to get there too.

or does this not make any sense?

I guess that would make sense, I was just surprised it went from mid 13 MPGs to low 15 MPGs. That's quite an increase I would think. Over 10%.

It could also be tbe weather changes too. I noticed a 2mpg bump as soon as it started staying above freezing around here.

My bet would be the changeover from the oxygenated gasoline used during the Winter to the non-oxygenated Summer blend. My Sierra's 5.3 goes up about 2 MPG once the gas changes over each Spring...drops in late Fall when the Winter blend goes into effect.

Might be old info, but here's all I could quickly find:

Gasoline Composition

We have already discussed two related changes in gasoline composition which decrease fuel economy: adding oxygenate and adjusting the octane of oxygenated gasoline. Adjusting gasoline volatility for seasonal ambient temperatures also requires changes in gasoline composition. Summer gasoline is given a lower volatility to avoid vapor lock and minimize evaporative losses. Winter gasoline (both conventional and oxygenated) is given a higher volatility to facilitate starting and warmup. The compositional changes required for the shift from summer gasoline to winter gasoline decrease the gasoline's energy content. Depending on the magnitude of the volatility change, the fuel economy of winter gasoline will be 0.5% to 1.5% lower than of summer gasoline.

Source: Chevron

Edited May 12, 200619 yr by BigPontiac

idk know how that could happen but i wouldnt be complaining

After i get a car for a while fuel economy goes up. After i can find out what the car can do I dont punch it as hard or accelerate fast or drive 100 on the freeway. so it could be driving patteren.