How to measure Fuel Requirements...

[Clois Harlan]

I just got off the phone with my machinist discussing the amount of fuel needed for my 428CJ w/ 2X4s. He gave me this formula and I thought I would toss it out and see if anyone agreed or disagreed with him. Here goes:

Gasoline engines need 1/2 pound of fuel per horsepower hour!
My engine has 450 Hp so I would need 225 pounds of fuel/hr.
Gasoline weighs about 8.25 pounds per gallon.
225 pounds divided by 8.25 gives me about 27.27gal/hr max use
at WOT.

To check my fuel pumps effeciency I first calibrated my fuel pressure at each regulator to 5.5 PSI. Next I disconnected my fuel lines at the carburator. I got a new plastic 5 metre measurement jar and had my wife turn on my fuel pump for exactly 30 seconds while I held both carburator lines in the jar. I measured just under 2.25 quarts of fuel in 30 seconds. So this would translate to 32.73 gals/hr. Based on his calculations I am almost spot on my fuel pump size. I hope I am quoting his formula correctly.

Has anyone heard of this formula or method of determining fuel requirements?

Clois

[Richard Hudgins]

Clois,

That is a correct formula. However, gasoline weighs from 5.8 to 6.5 lbs per gallon. (Specific Gravity of .69 to .78)

Therefore, (.5 lbs/hr x 450 hp)/ 6.5 = 34.61 GPH.

However, it is normal procedure to have a supply source that can provide 150% of the HP requirement.

(If this is really needed, I do not know. You will have to ask someone who has experience greater than mine.)

[Hotfingrs]

First, have never heard of figuring fuel needed that way....Second, your math is off...should be 67 1/2 gal/hr pumped...2.25 x 120 = 270 qts in an hr/ 4 qts gal=67.5....that's a pretty lame figure for an electric pump. My mechanical pumps output is 140 gal/hr....Most street electric pumps are in the 110-140 range.

[Hotfingrs]

After doing some more digging....@ 72 degrees a gallon of gas weighs 6.25 lbs

[Mr.Fixit]

If your motor noses over at the end of the dragstrip, you need a bigger fuel pump. (sorry couldn't help myself)

[Hotfingrs]

is that 1/8 mile or 1/4 mile strip?

[Chaplin]

With an FE, that's easy.

A lot

[Mr.Fixit]

Now that you brought that up, I am wondering about your car "running low 10's with no add ons" I always assumed that was the 1/4 mile, but you reminded me that in some parts, people consider an 1/8 mile a drag strip.

[Hotfingrs]

yep that's 1/4 time runs right at 6 sec for 1/8th

[sgianino]

Wow!! 10 second launches down the strip, thats almost classified as a funny car of some sort or top fuel dragster with them long wheelie bars in back

[Clois Harlan]

My math was off a little plus I took into consideration that my Aeromotive fuel pump is capable of 140 gph @ 14PSI. So I figure that for each psi the pump generates 10 gph. My carbs work most effeciently at 5-to-5.5 psi therefore I assumed at my carbs I should be getting 50-55 gph at WOT.

So, if we substitute the correct weight of fuel then 225 hp divided by 6.25 lbs per gal then my fuel requirement is 36 gph.

A dragstrip around here is 1/4 mile.

Thanks for the exact measurements, I was merely guestimating the weight of fuel, I think we use to call it a S.W.A.G.. I've slept since my last math or engineering class.

Thanks,

Given this formula does that mean that a Red Holley (97 gph at 7 psi) is only capable of managing a 303 hp engine?

[Clois Harlan]

By the way who runs 10's? I think the best I have ever turned in a 1/4 mile was a 11.97 and that was with drag slicks and about 60 degrees and low humidity. I hope I never stated I could turn 10's, if I did I was full of $hit! However, I have been known to embellish a little, but 10's?

Clois

[Mr.Fixit]

Originally posted by Clois Harlan


By the way who runs 10's? I think the best I have ever turned in a 1/4 mile was a 11.97 and that was with drag slicks and about 60 degrees and low humidity. I hope I never stated I could turn 10's, if I did I was full of $hit! However, I have been known to embellish a little, but 10's?

Clois

Hotfinger's car does. I was just goofing with him on that 1/8 mile question.

[Hotfingrs]

I run 10's. 10.5's with the 3.08 gears and 1.46 60' times...down to 10.1 with the 4.10 gears. Running 3.45 gears now.

[keithw]

Clois,

Did you get my email after I talked to Paula at Finish Line?

Keith

[Clois Harlan]

Keith,

No I didn't. My home year and a half old computer is getting a new hard drive and I am waiting on Hewlet Packard to send me the Recovery discs they failed to give at the time I bought my computer. Jerks are making me pay for them again.

I will call you on your cell in a couple minutes.

Clois

[Mr.Fixit]

Originally posted by Hotfingrs


I run 10's. 10.5's with the 3.08 gears and 1.46 60' times...down to 10.1 with the 4.10 gears. Running 3.45 gears now.

If I was turning 10.1's I don't think I would be able to resist the temptation to do everything in my power to get that car into the 9's. For some reason a 9.99 sounds a million times faster than a 10.01 when benchracing.

[sgianino]

Hek , I would shoot for installing a 427 into a Bike frame and go for 5 flat @ 280 M.P.H at that point.This reminds me of the Hemi commercial where the individual brags about having something the pick-up truck driver is lacking.........a parachute.

[Richard Hudgins]

Originally posted by Clois Harlan




Given this formula does that mean that a Red Holley (97 gph at 7 psi) is only capable of managing a 303 hp engine?

97 gph = 630.5 lbs per hour. (6.5 lbs per gallon x 97 = 630.5)

.5 lbs per hour per HP = 1261 hp. (630.5 lbs / .5 = 1261.) or conversely (630.5 lbs x 2 }= 1261 hp. {.5 lbs = 1 hp, therefore 1 lb = 2 hp}

The formula is the standard used by the SAE. Also it is the standard formula used by every race engine developer in the known world. (Well, some use liters per hour per kilowatt, but the equation is the same.)

Note: Look at any dyno chart and you will see reference fuel burn in lbs per hour per HP. It always is in the .35>.50 lbs per hp range. (Unless the tune is WAY OFF!!!!)

[George Snyder]

Hotfingrs,

What is the exact displacement of your SBC? Also any other details you would be willing to pass on about your engine?.

I am always curious. Just one SBC man to another!

Bud