is 2.5 hrs run time on 6 gallons of gas possible

so, i read something on the internet about this. i was busy over the weekend and now cannot find the exact article, but i believe the claim was that the guy running at the end of the feature heat of a demolition derby  had 4 gallons of gas left in the tank after running 2 1/2 hrs in a feature event. The rules clearly state a 10 gallon fuel tank capacity. Many people have made the statement that this is clearly not right. So i decided to crunch a few number.

so lets start with the obvious we have the following variables:

6 gallons of gas consumed, which by weight can vary a bit with fuel quality,but a good average for the weight of pump gas is 6lbs per gallon, and there are 16 oz in 1lbs.
6 gal X 6lbs X 16oz = 576 oz of fuel consummed

the modern gasoline engines burn at a ratio of 14 parts air to 1 part of fuel. actually true stoichiometric mix ideally is 14.7:1 but it usually ends up being 14:1.

so basically we just need to plug and convert the figures. Air/fuel ratio, or AFR for short, is determined by the weight of air divided by the weight of fuel.
AFR= Mass of air / Mass of fuel

or to get what we are looking for

mass of fuel X AFR = mass of air used

576 oz X 14 = 8064 oz of air

the CRC book of chemistry defines air as 1.2 oz per cubic foot. there are many other variables that effect the actual weight, measured using a barometer commonly, as well as relative humidity, but for the end result in this case, it is not going to effect it as much as you think.

8064 oz of air / 1.2 per cubic ft =6720 cubic feet

now 2.5 hrs= 150 minutes

which then means the said car was consumming a whopping 45 CFM.

do i believe this is possible to do with a V-8 chevy, yes, at idle. honestly this is an average cfm for a given time frame so obviously at times we can have full throttle and dead idle situations.

One thing to keep in mind is at 14:1 AFR, that is IDEAL conditions to get that ratio. this is why auto makers use electronic fuel injection, and sensors like the mass air flow sensors and throttle position sensor to bring an element of precision to the metering process to the induction process that simply cannot be achieved with a carburetor- let alone a carb in a demo derby. Relative air weight is probably less in the midwest  than the figure i used as i believe the 1.2 oz number uses sea level. I believe it is a pointless arguement cause it is obvious that the numbers are so far off from making any kind of  real power worth bragging about is ridiculous.

so then lets go 10 gallon at 1 1/2hr. to spare you all the bullshit, it works out on paper to an average of 125cfm. this is a lot more believable number using a SBC with a 350cfm carb geared rear axle, and smart driving, for derby use in a 5-6000lb. station wagon.

you don’t make horsepower without feeding the horse. it’s that simple. so don’t let anyone bullshit ya!!!

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