Autocross - Full or empty tank of gas?
 

Going autocrossing tomorrow and want some imput on how much gas I should have in my tank.

I have heard 2 different theories, both from auto-x instructors. Both claim to be faster.
1) As little gas as you need to make it through the day. This saves about a hundred pounds.
2) Full tank of gas. Helps handling since the gas is not sloshing around throwing off balance.

Has anyone tried both and seen a difference?

i would say bring as much as you need to get through a full day of auto-x. unless you're bringing jerry-cans. of all the things i've read about auto-x i would think "how much gas should be in my tank" would be somewhere next to "should i go with the pine, or vanilla air freshener"


edit; I say that because I would rather be slower because of a full tank of gas, then run out of gas half way through the day

If its your first event then keep it filled up..you won't notice a difference...But most of us will run with a 1/4 tank of gas...Each gallon weighs about 8lbs..

I did the last 4 runs of a pro-solo with the light on.

fuel pump does not like low gas.

hey, but what do i know. :)

beers :beer:

First event, definetely full tank. At events that I go to now, I generally show up with about half a tank.

Six pounds per gallon. It varies a bit depending on grade and temperature, but roughly 6.3 lb per gallon.

Water is 8.33 pounds per gallon. :cool:

And I would definitely run 3/4 to full tank on your first autocross. You've got other things to worry about! Enjoy the ride!

And when it's over, send your result to MAZDASPEED Motorsports. One more set of results and you'll be able to buy stock parts at dealer cost. Coils for $28.85, wires for $48, etc.

I have done this several times also. Never had an issues.

^ This is really good advice.

1/2 tank is the worst of both world. This will give you lots of extra weight plus maximum "slosh". Either full or empty... Anything in between will only slow you down.

Don't go below 1/4 is the guidance I've gotten to preserve the fuel pump and avoid starvation.

track days and autocross are two different animals. I wouldn't suggest going out on a track with the light on....

AutoX may not generate as much G force to create fuel starvation like in the circuit. I never have fuel starvation over 1/4 fuel. So close to half tank is AOK.

I try to just have the light come on on last or next to last runs, but as mentioned, having an extra 12 lbs (2 gal) of weight will not make a noticeable difference to your times. Running out of gas will.

Also, this may sound obvious, but if you are going to run it low, make sure there is a gas station nearby (and open on Sunday) so you can make it home!

autoXing -- you're doin it wrong.

you don't have as many instances of sustained (i.e., 3+ seconds) high Gs, but the peak Gs are definitely higher during autoX than on a track. plus the transitions on a track are MUCH less sudden and frequent.

we starved at a recent event on a not-super-grippy lot just after the light came on. the course was ~1 mile (low 80-seconds), and the light came on just before one run. we had starvation on the next run. i generally show up with just over 1/4 tank (but i have a co-driver).

We always started the event with a 1/4 - and even then got fuel starve on two occasions. On another occasion I ran the car completely out of fuel without a hiccup. The course layout has a big impact on when it occurs. But a 1/4 tank is safe most of the time.