I've always noticed that my 8 seems to have the most power when I just fill up the gas. As the amount of gas decreases, the car's performance steadily decreases. Not by much, but the power difference between full and near empty tanks is noticeable. Has anyone else noticed this phenomenon, and why does this happen? I thought that less gas --> less weight --> better acceleration. I also feel the same thing with my parents' Lexus ES300. Any ideas??

 

I thought I was the only one. I think it's psychological. We're relating our experience with running for a long time and then resting for a bit to drink some water. After quenching that thirst, we feel rejuvinated again. So... after giving fuel to our car, we psychologically convince ourselves that the car has been rejuvinated. Stronger and better.

I've ran tests and logs on my car to see if there was any proof that the car is running better and faster after refuelling. Well, my conclusion was "I'm imagining."

 

Just going on out a limb here. I know there is more weight when you have a full tank, but maybe that allows your tires to grip better? Who knows....maybe it is just all psychological. That's my theory and I'm sticking with it

 

I had my own theory for a while that the weight of the gas pushed more gas into the engine (remember the 3 holes in the milk carton experiment in elementary school?), so that the fuel pump doesn't have to work as hard when the tank is full. But then I'm sure that the ecu regulates fuel input, so that's probably not the case...

I am leaning more towards Xyntax's explanation of psychological re-energizing, except I equate filling up with eating instead of drinking. It feels like the car has eaten its fill and has gained more energy to run for a long distance... yummy 91 octane

 

I wonder if it's the balance of the car? With more weight in the rear, the car is going to transfer more weight back when you accelerate. So the perception of leaning backwards a fraction of a degree more translates into an impression of more acceleration? Dunno, it's a theory.

 

I almost always get best performace on the last 1/4 to 1/8 of a tank... after a fillup i can tell if the gas was "good" or crap by about the first 1/8th if it starts feeling sluggish...

i don't think is psychological either, the car runs WAY smoother, like all the good stuff was floating on top of the gas, and now I've used up the crap and I'm left with the cream....

 

I have also thought that, but along the lines that it is a slingshot effect: it takes more to move and when it does move it doesn't have to squat as much and so we feel it faster and more defined.

I feel it also with extra weight in the trunk and less fuel.

I have the stock suspension still.

Does anyone with a modified suspension feel differently?

 

I guess you car also have a better ride and is quiter after a good wash?

 

yup. better aerodynamics

 

put down the butt dyno and step away from the car please ...

 

Agree with teamrx, what a really lame thread.

 

+1

 

I think its because most people either fill up with gas

a) early in the morning before work or
b) at night.

Cool Air.

How much does a gallon weigh? 7 lbs? x10 = 70 lbs.

 

no math or physics are needed for this phenomenon. It's really just your imagination.

 

I think as the gas goes down, we feel we may need to worry about running out, so we become more gentle. At least I do. It's all the imagination and my right foot.