well i have alot more than 1500 into my motor and im at the 245hp mark and i get 20mpg freeway @ 3000rpm lol...
its all about effecincy... if you truley looking for a DD motor i would shot for around the 150-190hp NA mark... i think that will be just about as much as you can go before gas really takes a hit...
BTW if you want mileage STAY AWAY from the alcohol based fuels as it takes alot more per mile vs gas...
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