As long as you're not romping on the gas all the time and driving like a maniac, your mpg shouldn't suffer, even with an Si. It's a Honda. If you're complaining bout 30mpg, try driving an SUV, 6+ cylinder car, etc. I just spent around $35 to fill up 8.8 gallons and had just under 300 miles on the tank. And that includes a lot of spirited driving and occasional red lining.