Quote:
Originally Posted by FenwickHockey65
Small displacement turbocharged engine all depend on how you drive them. If you drive them like you stole them then you won't get any better fuel economy than their NA counterparts. Meanwhile there are a ton of Cruze ECO owners out there doing 45 MPG all day long.
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Yeah, I got better MPG than the sticker said on my Cruze and I'm getting better MPG on my EcoBoost F-150 than the sticker claimed. You just have to learn to keep out of boost when you don't need it.
Quote:
Originally Posted by Norm Peterson
My understanding of forced induction is that it needs to be calibrated a little richer than NA when under boost, so at the same power output as a larger NA engine it will use more fuel when they're both making that level of power.
It's because under conditions where you aren't into boost that the smaller FI engine drops back into essentially NA mode that you make any fuel economy gains. So it makes sense to let the turbo engine stay out of boost during the emissions and mpg certification as much as possible.
Whether that happens in any random driver's daily driving is a different matter, though I'd guess that you (as a mfr) wouldn't want the boost to be too far out of reach during normal driving lest the car get exactly the reputation that the V8 side views 4 cylinders in general with (a bog-slow low-compression NA 4). An enthusiast will tend to keep the engine at an rpm where boost will be available very quickly, while a non-enthusiast will tolerate longer periods of no boost and sluggish acceleration. Then again, when a 4 cylinder turbo is fitted with a manual transmission, even a non-enthusiast will tend to keep the transmission in each lower gear longer when driving in traffic.
I'm not going to chase down the data to argue overall cost of ownership other than to note (again?) that with an I4-T you have a simpler block casting, single exhaust with fewer catalytic converters and mufflers, and one less head with its valvetrain and associated controls. The financial advantage might still favor the V6-NA over the turbo-4, but it won't be by as much as the V8-NA enjoys over the V6-TT, where the V6 here still has the V block casting, a more extensive intake, the same amount of exhaust plumbing, and the same number of heads, etc.
Norm
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The bolded part is true, but with direct injection the difference is minimal. Add to that that DI is more effecient to start with, you do really realize some pretty good fuel economy with it. The problem is GM always tunes cars to be too rich to begin with. I understand why they do that on the FI cars--they can run on 87 octane without detonation, but I never understood why they do it on the NA cars.