Rep Power: 400

While this is stating the obvious, many people don't think of how much gas weighs and how it affects their car on both a road course or the 1/4 mile.

With say 13 gallons of gas in your tank, you have added almost 80 pounds of weight. (not to mention that weight can shift around while you're driving!)

While I know it is beneficial to try and have as little gas as possible when running the 1/4 mile, what do those who auto-x or road course race say? I've always wondered this.

 
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Id think they would need a little more than 1/4 racer would... I mean they are going into curve and stuff the gas shift and they may run lean if they are not carfull... that would be hella bad! just my ... 2 cents

EDIT: cute sig s2kman!

 
Rep Power: 365

I swear I get better gas mileage between 1/2 and E than from full to 1/2. And that's just normal driving.

 
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if by better mileage, you are judging by how long it takes the gas gauge to disappear after so many miles, don't. gas gauges are terribly inaccurate for the most part. though you may get slightly better mileage while there is less in the tank, since there is less weight in the car.

 
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ive personally noticed my car has much better pick up when im on the verge of cutting of

 
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well s2000man said the gas weighs stuff so it means that you are doing weight reduction so you will be slightly faster

 
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For autocross I ushually run half a tank... to guard against Fuel starvation. But I've run as little as a quarter tank and didnt have any problems, so maybe the pump pickup is in a good location... (in the Older civics you HAVE to run at least 1/2 a tank or else you fuel starve the engine... Had it happen to me in my friends STS preped 89Si, not fun.)

for general open track... Doesnt really matter much because you arn't competing, so I run with a full tank, so I dont hae to fuel up mid day and possibly miss a session.

Club Racing... well thats what Fuel Cells are for (Most racing bodys Require them)

 
Rep Power: 812

on the street, i always keep my gas 1/2 and below. best way cause it saves so much weight. i even drained most of the washer fluid out! hey its another 8lbs and I hardly use it.

 
Rep Power: 365

I don't trust the gas guage like it's gospel. My judgement is purely subjective. I notice a slightly better pick-up at lower RPMs when the gas is low, so I figure that I can rev even lower to get the same acceleration. Not scientific at all, but it seems right to me.

 
Rep Power: 335

the theory make sense. weight is weight, and liquids in large quantitys weigh a lot.

but i'd rather throw out all my passenger seats first, before using 1/2-fueltank as a weight saver modification. I always fill up every time i swing by the station since you never know if gas will rocket up 10 cents the next day

 
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how much does a gallon weigh? isnt it like 8lbs or something?

 
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6.08 pounds.

 
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ya when gas prices drop, I feel like stocking up. But I also like fresh gas and don't feel comfortable leaving gas in there for a month or more. Hence getting little at a time. But I do it mostly for the weight issue.

 
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I've noticed the exact same things as white2K2EX. From full to half it just flies.. From half to empty the car both revs faster and the gas needle just takes longer to drop. Hey, if it helps us in a mental kind of way, it's good enough..

 
Rep Power: 812

ya i'm sure it helps. When I used to fill up, I could almost feel the gas pushing the car around. Well not really but you could hear it swirling back and forth when you stop/go over bumps. That and I think the car is a bit higher up without the extra weight in the back (makes the drop more even with the front).

 
Rep Power: 413

I have heard that for auto-x it is better to run with your gas tank either on empty or totally full. If you have the tank half full then the gas can slosh around (shift weight around). So if it is full then there is no sloshing and if it's empty there is none at all.

 
Rep Power: 334

interesting..

i usually keep my tank 1/4 full only just for personal reasons. like if someone steals my car, bastard wont be getting enough fuel to take it very far. but currently, im trying to do a test whether the factory airbox unit will save mpg compared to an aem sri. so far, i filled up fill on the airbox. ill end up making a thread about it in the future.

 
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lol dude its a civic, even when the empty light comes on, there another 60-75 miles left in the tank.

 
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A gallon of milk weighs 8lbs.

 
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because they can't stop by a gas station and put in gas

 
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well, I don't know about you guys, but when I had my civic, I filled it up completely, and could only get about 5 days of driving out of it. If I kept it at 1/2 full, I would have been stopping for gas every 2-3 days. RIght now, my F150 can go 2 weeks without gas, I love it. it's a 35 gallon tnk which is 210lbs, but the truck weighs 6,200 lbs, so a full tank only adds about 3.3% more weight, not gonna make a big deal I think it's around the same ratio for a civic with a full tank of gas, but the civic has far less torque, so it's more noticable (I just drove my old 5MT civic today and realized this).

 
Rep Power: 365

Dude... 35 gallons? That must be a big fat bitch to fill up.

 
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Yeah lots of people say it must really hurt when I fill it up my F150... But really it's not that bad. When you pull into the gas station you just know the drill: slide your card, pull pants down, grab ankles, kind of like this . It's kind of like getting a series of shots, at first it hurts, but now you know what to expect and it really isn't that bad.

 
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you'd have to do the experiment 32 times with each, airbox and sri, and then also be sure it's done in the same weather and environmental conditions, as well as take the exact same path, with the same load and throttle position, etc. in other words, you're probably not going to find out anything conclusive. lol

 
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water also weighs 8lbs per gallon.

 
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ya you have to account for density

 
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is that whole, or skim?

 
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way to burst my bubble guys,

 
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weird because i fell that my car is faster with full/nearly full tank of gas. it feels like it pick up slower with quarter or almost empty gas.

 
Rep Power: 812

i notice that sometimes when I just finish filling and drive off. Maybe it has more pressure or something. but then next day its back to normal.