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post #1 of 21 Old 06-27-2009, 03:41 PM Thread Starter
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autox - full tank?

I've always run autox events with a full tank, but almost all the other mustang guys at the events run around 1/4 tank...

my reasoning for a full tank
-since the tank hangs off the back of the car, a full tank helps with rear-end corner-exit traction, the car just feels alot more planted.
-no added side-to-side momentum from a partially full tank sloshing around.

their reasoning for a partial tank:
-a full tank lowers the rear suspension travel slightly (& bind increase as the rear sus. gets towards it's end of travel).
-more understeer from the added weight at the backend from a full tank.

Input for either side of the argument?...

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post #2 of 21 Old 06-27-2009, 04:15 PM
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I've always tried to run with as little gas as possible. Usually it's something like 1/4 to 1/2 a tank. I'm no expert though.

Gas is around 6 pounds a gallon, so a full tank is around 84lbs. My car is heavy with not alota HP, so less weight the better in my head.

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post #3 of 21 Old 06-27-2009, 04:51 PM
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I like running with less gas, because less gas is less weight and less weight is easier to brake and to corner, even if it hurts accelerative traction. But some people claim the kind of sensitivity I never had, which is the effect of sloshing and the things it can do just after corner entry, and they like to run a full tank.

It would be fun to test it on a test & tune day where you had a lot of runs on the same course. Bring a couple 5-gal jugs, run it with a light fuel load for several runs, then fill it and see what happens to your times.
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post #4 of 21 Old 06-28-2009, 10:31 PM
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I run around a 1/4 tank in the honda. Less sloshy slosh. Feels like I can rotate the car easier..but that is what my butt-o-meter tells me...so who knows.
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post #5 of 21 Old 06-29-2009, 08:25 PM
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For me, a nearly full tank gave the "more balanced" impression. On the other hand, when doing rather quick transitions, it felt sluggish/slow to respond. On balance, I'm a half full guy.
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post #6 of 21 Old 06-29-2009, 11:00 PM
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I try to run 1/4 tank or less. It's the weight thing to me. I'm looking for any way to lighten the car a pound at a time. Why would I want to pull another 70 plus pounds in a car with no torque?

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post #7 of 21 Old 06-30-2009, 12:00 AM
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I never plan one way or the other. Sometimes Im on a full tank, other times 1/8 of a tank. Then again, I'm not that good of a driver so I can make up more time by not worrying about it. If I had to guess, it would be less likely to impact the stability of the car by have 1/4.

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post #8 of 21 Old 06-30-2009, 04:33 PM
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1/4 to 1/2 tank here. Beyond that it gets sluggish, harder to turn.

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post #9 of 21 Old 06-30-2009, 10:47 PM
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I always ran a full tank in my Mustang. Car seemed to put power down a bit better and generally went a bit faster with a full tank.

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post #10 of 21 Old 06-30-2009, 11:41 PM
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The difference between 1/4 tank a 1/2 for me is insane, it goes from no traction to being able to accelerate at apex.

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post #11 of 21 Old 07-02-2009, 09:47 PM
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i stay over 1/2 tank. anything below 3/8 tank and i get detonation under hard acceleration.

other than that, im not a good enough driver to tell the difference yet.

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post #12 of 21 Old 07-03-2009, 01:16 AM
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I've always been of the full tank camp but after the last event I competed at (too late/lazy to gas up the car and ran it at a 1/4 tank) and finishing ok in the standings, I'm changing my stance and am going to try running 1/4-1/2 tank for a few events and see if I can notice a consistent improvement.
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post #13 of 21 Old 07-03-2009, 11:55 AM
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I've autocrossed my 92 since it was new, and found a full tank was the best for me. As full as I can get it- I'll fill up at the station nearest the event. You need the traction. If you can put down full throttle consitently in second gear less gas may be better for you. If you don't run it full, run it 1/4 tank or less to minimize the weight sloshing back and forth in slaloms.

Justin
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post #14 of 21 Old 07-03-2009, 01:33 PM
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I have run my car at full, 1/2, 1/4 and as empty as I dare and while I noticed a significant difference in the feel of the car I am not sure it translated to better AutoX times. Subjectively the car feels more balanced with a full tank.
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post #15 of 21 Old 07-04-2009, 10:58 AM
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Toss the rear (metal) bumper and brackets - 40 lbs. weight savings.

That's worth 6-7 gallons gas in the tank.

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post #16 of 21 Old 07-04-2009, 11:07 AM
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When you say rear bumper, what do you mean exactly? Are they 5 mph bumpers or is this the thing that is going to save your life if someone rear-ends you?

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post #17 of 21 Old 07-04-2009, 11:15 AM
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Quote:
Originally Posted by BULLITT1992 View Post
When you say rear bumper, what do you mean exactly? Are they 5 mph bumpers or is this the thing that is going to save your life if someone rear-ends you?
Yea, those.

On my old "race" Acura Integra....I removed both front and rears. On this car, that I drive to/from work on occasion and also on track.....no way.

Something like this is a little more on the conservative side:

https://forums.corral.net/forums/show...weight+bumpers



(minus the parachute option obviously)


Last edited by 2k2GT; 07-04-2009 at 11:23 AM.
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post #18 of 21 Old 07-04-2009, 11:30 AM
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I ran the same setup for 4 years, stock engine with simple bolt-ons, stock suspension with lowering springs and Tokiko blue shocks, an 8 point cage, Cobra brakes, 17" street tires.

I found that I had no issues with putting the power down on a 160k mile stock engine, I filled up every time just outside of the track and ran through fuel during the day, filling with fuel jugs if I got to below 1/4 tank. My lap times were very consistent and didn't change much at all with fuel load. I believe the weight distribution kinda offset the weight difference. I read somewhere and I can't remember if it was MM (probably in a set of instructions that came with all of the stuff I'm still installing right now but can't seem to find it) or Griggs that said they preffered a full tank of fuel due to the weight distribution.

I really think your driving style and your car's setup will determine what is best for you. When I get back out there in a few weeks, I'm gonna do what I always did which is start full and go from there, maybe something will change for me with my new engine/suspension setup, maybe not.
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post #19 of 21 Old 07-04-2009, 11:53 AM
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Steeda makes a lightweight bumper replacement, but I was thinking of only using the one for the front. It supposedly saves 13lbs of the very front of the car. The rear saves 26, but if you use both, you are making your weight distribution go in reverse even though you are making the whole car lighter overall.

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post #20 of 21 Old 07-04-2009, 05:58 PM Thread Starter
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Just to follow up, I did morning runs at the local autox event with 1/4th tank, and afternoon with the regular full tank; definitely sticking with the full tank.

With the full tank the back end of the car felt much more 'settled' in transitions (though slightly more weighty/slower), coming out of turns I was able to put power down much earlier without the back stepping out & having to countersteer.

There was a very tight part of the track (e.g. 1st gear, almost full steering-lock) which was easier on 1/4th tank because it was much easier to slide the back out & get it setup at the right angle for the next apex...
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post #21 of 21 Old 07-04-2009, 06:16 PM
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Just like most things in car setup, it's all in what you/the driver feels most confident with.
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