Fuel Load

[crew21L]

How much fuel do you usually run for a heat race vs feature. Just curious. We always scale with 20 and have 55% rear and dont go much above 25 anytime but i have heard some people keep the tank FULL all the time.

[bullittwrench]

This is a good topic. Most chassis builders say to scale with 20 gal. in the cell. Do you have to? Running gas and 20 lap features, I don't need 20 gal. I scale with 12gal.@55% rear and start the feature with 15gal. Am I wrong doing it this way? I can't see carrying extra weight in the fuel cell when I can bolt lead on wherever I want it. Also does it matter if the fuel cell is mounted to the left if we're only running 20 lappers.


Thanks Guys

[billetbirdcage]

Fuel is just weight like lead so it really doesn’t matter (to a degree) if you use fuel for weight, lead or whatever; however the fuel load is behind the axle which can cause more of a pendulum affect. What is important is the amount of rear and the effect COG of the rear of the car.

Let’s say the 26 gallon cell is 16” tall and 16” wide and 24” long, so with 13 gallons the tank is half full that would put the top of the fuel level at 8”, so the COG of the fuel is at a 4” height from the bottom. If the tank has 19.5 gallons (3/4 full) the top of the fuel level is at 12” so the COG of the fuel is at 6” plus it also weights 45.5# (6.5 gallons x 7#) more so there is more weight and it is higher in the rear of the chassis. This will induce more roll.

You can simulate this with lead fairly closely (limited by lead placement because of cell in the way), but is something you should think about because as you add fuel you will also raise the rear COG of the car plus add rear weight.

Obviously the fuel is going to move around in the cell somewhat depending on any anti-slosh that is in the cell.

Adding fuel is an easy what to add rear percent and raise the COG at the same time. It is far more convenient then bolting on a piece of lead.

The reason most still say to scale with 20 gallons is likely from the older days when we ran alky and with a longer race and fuel burn off, that would be the likely amount of fuel you had left. I just like to scale with the amount of fuel I have left after a race, so if I normally fill the cell completely full before the feature (26 gallons) and burn 6 during the race; I would scale with 20 gallons. The 20 gallons still seems about right now on gas because we don’t burn as much but the cells are usually around 22 to 26 gallons instead of the 32’s we had with alky.

It is a good idea to scale once with the cell real low and start adding 5 gallons at a time so you can see what happens to rear, left percents, and LR bite, this way if the track is real heavy and you wish to remove some rear by lessening the fuel load you will have an idea of what it does to the rear and left percents as well as if it gains or losses LR bite and can adjust accordingly if needed.

[Hendrens Racing Engines]

One thing that concerns me is when you fill the cell to the top would have very little room to crush the cell in a hard impact increasing the chance of a ruptured cell.a cell thats 3/4 full will be a lot more forgiving in a hard wreck in the first few laps.

[billetbirdcage]

Very true!

[MasterSbilt_Racer]

I don't know if it is right, wrong, or indifferent, but I like to position the cell such that no matter how much fuel is in it the lr stays the same.

[crew21L]

All good info, but I am still curious how much fuel everyone has in the tank when they go out for a heat and a feature.

[bullittwrench]

We start the heat with 12gal. and the feature with 15gal. running gas.

[billetbirdcage]

8 to 10 laps heats and 30 to 50 lap features:

26 gallon cell:

18 heats and close to full for feature, how full depends on length of race and if rear percent is needed or expected fuel use. (hammer down or slick)

[MasterSbilt_Racer]

I start with 20 on gas and full on alky.

[2dumb2kwit]

I scale and start with 14" in a 32 gal. cell. (about 25gal) Doing everything at the same fuel load, leaves less of a chance of me confusing myself.(I do that enough, already.)

[FlatTire]

I try to start the heat race with 12 gallons and start the feature with 22 most nights. That's with alcohol and a 2350lb weight rule. It varies with track conditions and the amount of mud we expect to pick up on the car.