VetteDrmr

I understand that you want to run with the least amount of weight possible, but I've never figured out how much to start with.

The C5 has the saddle bag tank system, and coupled with its indescribably accurate gauging system on the C5s when the fuel levels are low, how much fuel do you start the day with?

TIA, and have a good one,
Mike

XPC5R

Used to start with a 1/4 tank indicated in the '01. The car would run strong until the reserve fuel warning came on - it would occasionally starve then.

yellow c5r vette

I used to slalom a c4 alot and we ran it 1/2 and abouve to keep rear weight.
If you use a 1/4 on the C5 (tanks further fwd) would you not need more?
In any case a lot of it is personal pref and some trial and error.

Can I ask about duration of fuel on any tack days without starvation?

gonzalezfj

Mike, every C5 I have seen (quite a few) will dependably draw fuel from the tank until the "low fuel" alarm activates. After that you may run into some fuel starvation during high-G maneuvers.

We run our C5Z at 1/8 to 1/4 tank for two drivers = 6 runs.

Frank Gonzalez

Bill Dearborn

With the C5s I have run anywhere from a half tank to a quarter tank with no problems. The amount of fuel is determined by the number of drivers and the number of runs. Once the low fuel indicator is on I do get some starvation in high g turns.

With the C4 I always ran with a full tank to minimize the affect of fuel slosh in the tank. With the fuel tank mounted behind the wheels and if you ran a 1/2 to 1/4 quarter tank of fuel you could disturb the handling when the fuel moved from one side of the tank to the other. It is like a big slide hammer varying from 55 to 30 lbs moving back and forth across the tank.

Bill

VetteDrmr

Frank & BPC5R,

Thanks for the data. I think I'm finally getting my skills down to the point that I can start working more and more on car setup. Figure fuel weight is one thing easy to start working with, I just didn't want to get into a fuel starvation issue.

Y'all have a good one,
Mike

TedDBere

3 gallons. I run her down and put $10 in before an event. That's just about 3 gallons for a 6 to 8 run event.

GrantR

I'll often do my fastest run of a day with a passenger. I figure if 150-200 lbs of passenger doesn't seem to noticably slow the car down, then fuel level doesn't make any difference to me. There's always far more variation in my driving from run to run and more to gain by simply trying to get a good consistantly fast run in than the gain from running low fuel for me to bother with dealing with only part filling the tank before and after every single event.

(But yes, of course, less weight will generally produce faster times, probably by only a tenth or two per 60 seconds)

gonzalezfj

Most serious autocrossers would sell their mother into slavery for 2 tenths of a second in each run.

Frank Gonzalez

GTB/ZR-1

There's more than likely a good reason for that. I assume your car hasn't been optimized by corner weighting, so your passenger is actually better balancing your car w/ their weight.

To answer Mike's question--Like most above, I run as near empty as possible

VetteDrmr

Grant,

That's exactly what I've been dealing with the past couple of years. At first my passengers were always instructors, therefore the faster times. Then when I saw the same thing with non-instructing passengers I started suspecting my ride height.

Sure enough, this year I found that my LF-RR diagonal weight was 150 lbs less than the RF-LR. So, I raised the RR one full turn; I'm going to re-weigh the car this weekend.

So, the moral to the story? Make sure your passenger weight always consists of instructors!

Have a good one,
Mike

acrace

I like this topic.

Does anyone have DATA that shows the difference at 1/4 tank versus full tank for, let's say, a 20 to 40 mph, 30 to 50 mph (or something autocross comparable) acceleration run?

Solofast

How much fuel to run, as they say about with many other things "it depends"

Last year we ran the C5 as close to dry as possible, and were fine on putting down power. This year we changed the amount of jounce damping in the rear and couldn't put down power coming off corners worth a darn. At a test session we were running harder and harder, and not going any faster as we made changes. The lower the tank got the less acceleration we could apply coming off of corners. We filled the tank and SCHAZAM!!! we were putting power down. So, it depends on how your car is set up and what shocks you are using and how they are tuned. That said, I am going to go back to the older shock settings so that I can run without the extra fuel weight. But there are times and conditions where you can adjust the ballast (fuel weight) and take advantage of it (insert location of an important event or course where you think you might be on slippery asphalt here )

The lesson being that if you tune for it you can run low and should, but if you are finding wheel spin coming off of corners put some fuel in it....

XPC5R

Solofast is right on the money - with our setup, the heavy fuel load improved power down to the point of pushing. The light load was more balanced, and also slalomed better (less polar moment) - the heavy load had after a few cycles a distinct pendulum action from the rear. This could be tamed with rebound adjustment, but that had other interactions.

I chose to run the car light (we were down in the high 2800's) figuring that benefit is seen in all directions (lateral and accel/braking). But coul dsee adding more fuel if the surface was slick.

VetteDrmr

Solofast and BPC5R,

When you say "run more fuel", would you go from empty to full? or half?

Man, by the time I get a feel for this the day's going to be over by a month or so!

Thanks for the continuing education (now if I can just figure out how to use it!), and have a good one,
Mike