Quote:
Originally Posted by Deslock
It'd be great if the US-spec ND 2.0L gets rated at 30+ MPG city, but it's not guaranteed. Assuming shorter gearing and engine tunes/tweaks for better throttle response and more output, I expect it wont be that efficient.
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Okay sure some power-increasing engine modifications will decrease mpg, like oversized valves (very slightly). However these days it's more common to just slap on a different manifold and call it a day, and those basically don't affect mpg. ECU tuning at the OEM doesn't decrease mpg, at least not for testing purposes like I said. They might spec thicker oil or something and that might decrease fuel economy by like 1%, again not much. A different cam profile could affect things, but again from the OEM, you're not going to get any drastic changes. Besides, bigger cams give you lower pumping loss, which cancels out some of the loss due to inefficient combustion.
It depends on how the shorter gearing is done. A substantially shorter final drive will ruin the EPA test numbers, but a close ratio gearbox with the same final drive won't because your 1st and 2nd gears will be pretty close to the original, and the main waste of fuel in the EPA city cycle is running the car in 1st gear and 2nd gear too much. Typically for sporty cars you see a close ratio gearbox and often times a shorter final drive as well, sometimes just one, but I think the closer ratios are more likely.
Another unknown factor is if they choose to specify shift points. If you officially recommend to shift out of 1st at 2000rpm, then you'll show significant improvement on the EPA test. I think most manufacturers are content to let the manual transmission die off so they don't care about this, but not always. The Ford Mustang and its 1-4 forced skip shift did wonders for its city rating, even though in the real world it probably doesn't actually help for most drivers.