Quote:
Originally Posted by switchlanez
So the new FB20 engine in the 2012 Impreza is 2 liters and gets 27 city/36 hwy mpg with CVT and 25 city/33 hwy for the 5MT. But it outputs 150 hp on the 2,900 pound Impreza.
The FR-S/BRZ's FA20 is based on the FB20. Also 2 liters but difference is it's been tuned to 200 hp. The D-4S direct injection is supposed to increase hp and fuel efficiency but I think the engine has to run richer (consume more gas) to achieve the huge +50 hp bump and tuning is skewed more towards power than efficiency. The FR-S/BRZ is 200 lbs. so that helps.
200 lbs. lighter but +50 hp? I think it would have the same or worse efficiency numbers than the 2012 Impreza. Also, CVT makes a difference which our car won't have. And Impreza's 5MT is geared for fuel efficiency; our 6MT should be geared for some mix of performance/fuel efficiency.
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Errr...the engine only runs rich near max load and idle. And direct injection reduces the amount of fuel you need because it improves combustion efficiency and reduces cylinder temperature. In addition, the long duration cams reduce pumping loss, and the direct injection makes up for the lack of charge motion due to high lift. If anything, the FA20 should be the more efficient engine at every point.
Anyways, CVT would help in the city, but would hurt on the highway because it has high frictional losses. The manual transmission doesn't have a very tall 6th gear so it won't cruise near max. efficiency, although based on my calculations it should be able to pull a respectable 40+ mpg at 60mph. The auto has very tall 6th gear so it could hit 50mpg. Also you have to remember, rolling resistance is a very small force compared to aerodynamic drag. The Impreza is much bigger dimensionally, and will have more drag.
EPA highway != highway cruise mpg. EPA highway test includes lots of slowing down, speeding up, etc. I dunno about other people, but on the highway I almost never need the brake, and I certainly do not slow down to <45mph very often.