[tboudre]

Originally Posted by lightsareout

I have a 328xi and recently started a new job and drive 80 miles round trip each day. What mods can be done to improve the gas mileage of my car? I'm already looking at a k&n drop in filter and the charcoal delete.

I was in your shoes a couple years ago, driving a new Infinti G37 about 150 miles/day round trip and spending $500/month on premium fuel and I tried just about anything, aside from a tune, as that would have cost over $500 and tunes are designed for power, not economy, though some report increased gas mileage. One trick was to put 3-4 oz of acetone per 10 gallons into the tank. It was supposed to help atomize the fuel better. I couldn't see any recognizable gains in MPG. I bought some of these vortex things to put in the air intake that were supposed to swirl the air and mix it better. All it did was created a restriction in the intake and made the car very sluggish to respond. Perhaps after the computer adjusted to starving the air from the car I may have had some mpg gains, but who wants to choke a 300hp card down to 200hp? The best thing I could do was keep my foot out of it, I'd allow myself one or two WOT accelerations per day, but keep it on cruise control. I was adamant about putting pure gas in the car, as the 10% ethanol would give me lower mileage. But it was to the point that I could have cheaper gas and get lower mileage or get better mileage with more expensive pure gas, and it would be about the same either way. All the while putting premium fuel. I ran across an article recently. It proposed that E10 (what is available at most pumps, up to 10% ethanol) is the absolute worst mix that you can run for mileage. They found that certain cars, with no modifications, could run E30, E50, or sometimes straight E85. They also found that a mix of E20 or E30 in some vehicles resulted in the same mileage as pure gas or sometimes better. Of course, the main thing isn't the MPGs, it's saving money. What if I told you that instead of paying $3.79/gallon for 93 octane that you could buy 5 gallons of E85 at 105 octane for $2.89.gallon, and mix it with 10 gallons of 87 octane at $3.14/gallon and end up with a mix of about 30% ethanol and 93 octane? You just saved $11 on a tank. Of course, I do this now, since I no longer have a long commute, and I have the 335i and the JB4 tuner, and I get a buttload more horsepower from this setup for a couple of different reasons that are not relevant to this discussion. Any car should be able to do this, but YMMV, and, as I understand, if you start getting into higher E%, a tune may be necessary, and possibly some other mods.