Weight reduction: not filling the gas tank

[MetroMPG]

Hrm. Kinda goes against the whole water injection philosophy.

If I went all the way from F to E, I'd only be filling up once every 3 months.

Think I'm going to go outside now and siphon some gas out of the Flea.

[SVOboy]

His is very anti-water injection, but seriously, how much water could be in the air in the gas tank compared to the humidity in the air you're sucking into the engine in huge quantities?

[kickflipjr]

You could take it a step further and buy a 3 or 5 gallon race fuel cell for your car.

[omgwtfbyobbq]

It'll help with acceleration more than FE. The energy required to accelerate a 2500lb car ~25 times to ~40mph is only a fifth of what is required to cruise at ~20mph for ~30min. More to the point, engine efficiency alone isn't why 80,000lb semis get about the same mileage as 10,000 hummers. FE is all about CdA, and acceleration is power to weight. Sadly, EVs with small gensets can provide both.

[MetroMPG]

You're right: the weight reduction would be a city driving advantage more than a highway / cruising benefit. Which is fine - because those times you do need a full tank for highway cruising, it doesn't really hurt to fill 'er up.

I like the wee gas tank. Put one in and tell everyone you have a "fuel cell" car.

[omgwtfbyobbq]

Put it on ebay as experimental hydrogen tech, someone will buy it for ten grand! But srsly, if you only keep a gallon or two in your tank you'll improve acceleration by ~3%, FE by a much, much smaller amount.

[Ted Hart]

Originally Posted by theclencher

I wonder if the increased fuel sloshing around when at less than full causes more evaporation?

For..."theclencher"-
And, where is this "evaporated fuel" going to go? A volatile liquid ...in a closed container... rapidly saturates the space above the liquid...and, as such, the space cannot take any more molecules of vapor. Unless you heat the liquid. Then, the vapor pressure goes up...to equilibrium. The molecules jump out of their liquid state...and saturate the space above... until equilibrium occurs, then everything stops. The fuel won't evaporate in a closed container.

[zpiloto]

I experimented with this(nothing hardcore just comparing tank averages) running several tanks with 5 gallons compared to the usual 15 gallons with no noteable increase in FE. It does accelerate better but I didn't like filling up every 3-4 days.

[JanGeo]

I remember when the Geo got down to 1/4 tank or lower it really takes off at a stop light and pegs you back in the seat compared to it with more fuel in the tank. Guess the fuel is a higher percentage of the weight in it.

[ZugyNA]

Originally Posted by theclencher

Yes, the vapors get trapped by the canisters and eventually combusted in the engine. But how much vapor is there, and does the engine recognize it and adjust fuel injection leaner to compensate? In other words, even though the vapors are combusted, are they "wasted"? It's all just a hypothetical question. Without quantifying anything, I would guess that vapors and fluid losses generated within gas tanks are minimal.

My 300Zx gets maybe 10-15% better mileage thru the first 4-5 gallons of a 19 gallon tank. I assume it is the fresh vapors from the new gas going thru the canister.

One guy has set up a continual air bleed from the tank and claims better mpg...except for the first few gallons.

Note: this can cause your gas tank to collapse if it isn't vented at the cap...backflash could be fatal.