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Old 03-31-2020, 05:05 PM   #108
Chance
Senior Member
 
Brand: Still Looking
State: Texas
Posts: 6,187
THOR #2121
Fuel economy versus engine size

Since this is the technical section, and so many of us are bored stiff having to stay in place, I thought we could discuss what happens to fuel economy when engines are too small, too large, or just about the right size for the job at hand.

I’m aware most people only care about how much we spend on fuel/gas, but a few of us may be interested on how we get to that point in greater detail.

A few unscientific fuel-economy data points are starting to roll in for the new Ford 7.3L V8, and results comparing to other engines of different sizes are not completely unexpected. However, in my opinion it helps to consider results in proper context.

As a starting point for discussion, it’s interesting to see what happened when TFLT pulled the same trailer at 70 MPH with three pickups ranging from RAM/Jeep 3.6L V6 up to Ford 7.3L V8. And to make it more interesting, a Chevy 5.3L V8 is right in the middle of engine displacement.

Jeep with 3.6L V6
285 HP and 260 lb-ft torque
8-speed with 4.10 gears
11.108 gallons
5.9 MPG

Chevy with 5.3L V8
355 HP and 383 lb-ft torque
10-speed with 3.23 gears
8.033 gallons
8.2 MPG

Ford with 7.3L V8
430 HP and 475 lb-ft
10-speed with 3.55 gears
8.534 gallons
7.7 MPG

Please keep in mind that there’s not a lot of accuracy here since measuring 1/2 a gallon of fuel difference with a normal gas-pump fill-up is not exact. Still, it shows a trend that could be predicted.

For what it’s worth, none of the trucks pulled the trailer in top gear, so differences in final axle ratio is secondary (plays a role but is not critical). Overall ratio and engine RPMs was affected mostly by engine size and associated capability.

Anyone surprised with MPG results? Thoughts?
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