Fuel Requirements

[BobbyB]

How many gallons per hour of nonethanol gasoline are consumed by an engine that makes 420 peak horsepower at 90 percent volumetric efficiency? Is more information needed to make an estimate within 10%?

[GARY C]

How many gallons per hour of nonethanol gasoline are consumed by an engine that makes 420 peak horsepower at 90 percent volumetric efficiency? Is more information needed to make an estimate within 10%?

I don't know if this helps, I think he was using low led 100 octane av gas.

[David Redszus]

How many gallons per hour of nonethanol gasoline are consumed by an engine that makes 420 peak horsepower at 90 percent volumetric efficiency? Is more information needed to make an estimate within 10%?

Displacement and RPM?

[BobbyB]

350cid at 5000 rpm

[BobbyB]

Thanks Gary C,

Based on the dyno sheet Gary posted, I figure:

183.2 lbfuel/hr x 99%/90% x gallon/8.34lbH2O x lb/.72lb fuel = 33.5 gallon fuel/hr

Is my figuring close to correct?

[David Redszus]

Thanks Gary C,

Based on the dyno sheet Gary posted, I figure:

183.2 lbfuel/hr x 99%/90% x gallon/8.34lbH2O x lb/.72lb fuel = 33.5 gallon fuel/hr

Is my figuring close to correct?

A 350 cuin at 5000 rpm will consume 41 lbs/min of air and 3.26 lbs/min of fuel.
Subject to fuel stoich and SpG and air density.

[BobbyB]

Thanks very much David.

[F-BIRD'88]

A 420 hp engine needs 42 gph.

[BobbyB]

Thanks Fbird.

[Mattax]

For estimating maximum fuel consumption I've used the relationship of 0.5 lbs/hr for every 1 horsepower.
I *think* its from Urich & Fisher's Holley book as a way to figure what fuel pump to use.
So just for curiosity how close this rough calculation compares.

420 hp x 0.5 lbs/hp = 210 lbs/hr
210 lbs/hr divided by 6 lbs/gal = 35 gal/hour

Since this was a calculation for maximum fuel requiment, my guess is that less than 100% VE was assumed. Prob based on 95%
Looking at the dyno sheet above, that engine was consuming 0.5 lbs/Hp-hr at 97% VE so this all seems to be ballpark correct.
Not sure why David's estimate is so different.

[jacksoni]

David's estimate of 3.26 lbs/min is 32.6 gal/hr which is not so different and if you use a somewhat better BSFC than the .5lbs/hp/hr you are using which many engines will beat then yours is even closer to his.

[Mattax]

David's estimate of 3.26 lbs/min is 32.6 gal/hr which is not so different and if you use a somewhat better BSFC than the .5lbs/hp/hr you are using which many engines will beat then yours is even closer to his.

Thanks. You're correct.
I misread 3.26 lb/in as gals/min

[David Redszus]

Fuel consumption at full load (open throttle), is not dependent on horsepower.

It is determined by displacement and rpm. Assuming some air density, we obtain air mass.

For a given air mass, the fuel mass is determined. From a design perspective we always use the stoich
value for a given fuel, which when combined with SpG, allows us to determine the number of gallons needed.

This is then converted to injector flow rate and injector duty cycle for fuel mapping purposes.

Often the actual stoich value and SpG is not known, and neither is actual air mass ingested, resulting in errors.
In addition, racers will often use excess fuel to control inlet temperature and/or detonation. This also throws the calcs into a waste basket.

It is interesting to note that the Mercedes Benz Formula One team was fined at Singapore for attempting to use fuel that was too low in temperature.

[Geoff2]

The displacement doesn't change throughout the rpm change. The density of the air drawn into the cylinders does. The original Urich/Fisher formula for fuel reqd v HP in the Holley book is as valid today as the day it was written.

[F-BIRD'88]

Yes it is dependant on horsepower output.
2 different 350 sbc's . 1 makes 400 hp @ 5700 rpm.
The other makes 435 hp at 5700 rpm.
The 2nd motor has better volumetric efficientcy thus consumes more air and fuel @wot.
And as result makes more power by burning more fuel.

Horsepower divided by 10 = fuel system flow requirement (with a bit of insurance) for selecting a fuel pump. Real gph output @ the working pressure thru the system.
500 dyno hp wants 50 gph.