Quote:
Originally Posted by Phase
not if you have a smaller engine. my ioniq has one of the lowest drag coefficients on the market, but mpg tanks above 55 because of the smaller engine
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This seems to be very true.
In some of my older cars I could get the best fuel mileage around a constant 30mph. Slower or faster would make it get worse fuel mileage. Those cars had smaller engines and less overall power.
The Avalon has one of the biggest engines I've ever had, and it seems to get it's best fuel mileage around 50 to 55mph. Below 45 and I notice a drop. Above 60 and I notice a drop.
But I still think it's the aerodynamic drag. Even a small engine will tend to run at lower than optimal BSFC load at speeds of 60 to 65mph, or even 70 to 75mph, unless your engine is so small you have to keep it pretty much floored to maintain those speeds. If you still got some acceleration in top gear at those speeds, chances are it's not that you're passing optimal BSFC.
The exception is in vehicles that they gear way too low in order to make them peppy with small engines. Some small engine cars are geared so you don't hardly have to downshift at highway speeds anytime you need some acceleration. Ideally you want to be close to full throttle to be in the most efficient zone. But that doesn't leave much room for accelerating without downshifting. So you end up with a setup that's running at some 3,500RPM and a half throttle down the highway instead of some 2,000RPM at three quarters throttle, which would be more efficient.
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