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Old 07-16-2011, 11:51 AM   #1
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Hi everybody

Hi my name's kyle i drive a 2007 cobalt lt coupe 5 spd 2.2 ecotec.
i only drive this car from home to work and back between two jobs combining highway and city i'm averaging 31.1 mpg at the moment and it keeps rising.

my main things i'm doing are light accel with a shift religiously at 2500 rpms and typically have my windows open including my sun roof for aero purposes. soon will be adding a k&n air filter because i believe as a mechanic that normal paper filters restrict the flow of air. Working on an idea for my exhaust at the moment to increase from the stock 2 in pipe and restrictive mufflers to a 2 1/4 system custom welded and built by me into a larger muffler with better flow.

hopefully i will successfully reach upwards of 40 mpg! the cobalt xfe supposadly gets 32.3 and i have a normal cobalt so i'm creeping up on that as we speak.

id love to hear any ideas or stuff successfully done to a cobalt please let me know. nice to meet everybody!
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Old 07-16-2011, 02:18 PM   #2
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Re: Hi everybody

welcome!

let's start by saving you some money...

a k&n filter and custom exhaust will yield a negligible amount of mpgs, and certainly would not be cost effective enough to pay for themselves in fuel savings.

if your car will allow, i'd suggest shifting at or below 2k rpms. also, at highway speeds, close your windows and run the a/c--it's a more efficient strategy.

inflate your tires to the max of side wall recommendations.
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Old 07-16-2011, 03:02 PM   #3
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Re: Hi everybody

Welcome.

I agree with what bowtieguy said above.

Regarding intake and exhaust: Consider how much power the engine can make (and the flow required for that), then consider how much power (and flow) you are using for economic driving. It's a fraction of the maximum airflow and should flow quite freely. GM's engineers are no fools, with ever-tightening CAFE regulations and the continued popularity of big trucks they can't afford to leave any easy MPG on the table when they design the Cobalt.

Few modifications to the car will pay for themselves; modifying your driving will. Keep an accurate gaslog and experiment with different strategies.

It would never pay for itself, but if you transplanted the transaxle and PCM from a Cobalt XFE (I think those are the main differences, plus LRR tires) you could probably get a big jump in FE.

There's a good chance that your car has a wideband O2 sensor. If so, you may find that accelerating with WOT (and shifting low enough to control your acceleration) will provide better FE. If not, 70-90% would likely be best, as much as possible without hitting open loop. Doing it that way reduces pumping losses at the throttle* and reduces friction and reciprocating loss, which leverages increased volumetric efficiency available from your engine. 2500 RPM is almost certainly too much for the best FE.

* Going back your concern about pumping losses in the intake and exhaust: As long as the throttle is closed, it's a much worse restriction than either of those systems.

P.S. If your motivation for saving fuel is something other than saving money, then obviously the concerns about what will and won't pay for itself are irrelevant.
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Old 07-17-2011, 05:14 PM   #4
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Re: Hi everybody

Try taking you right shoe off and very softly use the gas pedal, shift at 1500 rpm for every gear and see what lightly really is. You will be amazed at the difference. My mpg went up just by doing this.
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Old 07-19-2011, 07:31 AM   #5
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Re: Hi everybody

welcome! and i actually drive the same thing. but on theholycows note.

my car actually is an XFE but theres honestly not much different. a slightly different tune. and taller tires but there are not really anything else different.
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Old 07-26-2011, 06:01 AM   #6
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Re: Hi everybody

thanks for the info guys i'll keep posted on here as far as my exhaust goes i've decided not to just because of the fact i've learned i have an emissions warranty until 80000 miles so i'm not going to compromise that lol.

i've seemed to notice that when i'm shifting at 2500 each time light throttle i've been climbing up my mpg scale but it seems when i drive like i'm not trying to save gas i actually get a better climb??

the whole ignition off on coasting and at stop lights as far as that goes my car did not like that at all lol it actually forced my gas gauge and my hvac systems to have a relearn and freaked me out a little so don't try that.

so you guys are saying if i accelerate almost wot at a low rpm i'll increase my fe??
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Old 07-26-2011, 07:14 AM   #7
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Re: Hi everybody

WOT low RPM acceleration worked great for my 2008 VW...it certainly won't work for every car but I wouldn't be surprised if it works for yours.
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Old 07-26-2011, 08:48 AM   #8
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Re: Hi everybody

keep in mind though too is that wot with low rpm is going to be harder on you clutch pack and flywheel also because of the friction.
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Old 07-26-2011, 09:04 AM   #9
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Re: Hi everybody

I don't see how, unless your clutch is slipping...which means it already needs to be replaced.
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Old 07-26-2011, 09:46 AM   #10
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Re: Hi everybody

i guess it depends really but you definately need to be careful at which steps you take to the extreme because they could prematurely damage your car.
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