Quote:
Originally Posted by stillsearching
6 answers and still not answered. 
Not asking about power, or controlling boost, i'm not asking about people using their left foot to ruin MPG, not talking about hillclimbing with more power at lower rpm... i'm talking about i've never seen ever any automaker put out two versions of the same engine (one with turbo and one without) where the turbo version even matches the MPG of the nonturbo one. The EPA driving cycle accelerates and loads all engines about the same. I would assume that a light foot and staying out of boost should in theory leave you with the same mileage. I would assume its "right foot controlled" but i've not seen that.
I don't know if it's just the backpressure worsening mileage (when it's not in boost) or whether the turbo reducing the vaccum in some way impairs it. (I'd heard for mileage to drive at steeper vaccum if you have a gauge) Or maybe the presence of the turbo prevents that super high load condition (like used by pulse and glide drivers) where the BSFC island is at it's best?
SOOOOO i'm wondering why there isn't just a complete turbo bypass ever implemented, similar to having exhaust cutouts on some cars, even if it has to be heat resistant. For that matter you might even have a three way cutout - two different turbos for different load conditions (lower rpm torque, higher rpm performance) plus a total cutout for best MPG keeping high load unladen.
I'm hoping someone who knows the physics of turbos better maybe could tell me why it's not a good idea to put in a cutout.
PS Balto cute avatar. And in the theory of the Saab Light Pressure Turbo and the Ford Ecoboost I should be wrong, but according to the EPA figures for basically every turbo engine i've seen it doesn't show under their test cycles. |
Thanks, that's my fursona :3.
I have never seen a factory turbo car that has the same gearing ratio as the NA version. The turbo version always has a shorter ratio to make it feel more 'sporty'. Thus, Killing the mileage. Also no manufacturer in the past has economy in mind when tuning the ECU and other systems on a turbo version.