Left Field
Well-Known Member
- First Name
- Tim
- Joined
- Aug 5, 2020
- Threads
- 18
- Messages
- 442
- Reaction score
- 969
- Location
- Western WA
- Vehicle(s)
- '67 RS-SS Camaro, 2021 JLUR392
- Thread starter
- #1
During Jeep travel sometimes a person has time to ponder Jeep things. My ponder was how much horsepower was my engine putting out while I'm traveling. Different speeds, up long inclines, with a trailer, etc.
Turns out fairly simple to figure - assuming I got it right anyway...
*** Nerd warning - proceed at caution ***
?
(or just skip to the numbers further down...)
Wikipedia has 'Gasoline Energy Equivalence' tables. They show a gasoline equivalent fuel energy (GEFE) of ~45 HP-Hrs / gal.
Another helpful Wikipedia table listed 'Brake Specific Fuel Consumption' data for a broad cross-section of engines, including both gasoline and diesel. This data measures the net crankshaft brake horsepower output per the amount of fuel consumed.
From this info a mechanical power output the efficiency can be determined (and is provided in the same Wikipedia table). Modern automotive gasoline engines ranged mostly in the low-mid 30% range, so I picked 33% as a ballpark efficiency value (EFF). A DI gas engine would be higher, and a diesel higher yet, but my engine is MPFI so that seemed reasonable.
Calculating gallons per hour consumed is easy: MPH/MPG = GPH
Not much harder is the net engine output horsepower: GPH * EFF * GEFE = HP
Or combined: MPH/MPG * EFF * GEFE = HP
somebody stop me, please ?
So plugging in some data to get engine output numbers...
Jeep down the highway at 60 mph and 17 mpg: 52 HP
Jeep down the highway at 75 mph and 13 mpg: 86 HP
Jeep pulling a camp trailer at 70 mph at 11 mpg: 95 HP
Jeep pulling a trailer up a grade at 65 mph at 5 mpg: 193 HP
Jeep on a rough trail at 10mph and 10mpg: 15 HP
and of course...
Prius zipping down the highway at 60 mph and 50 mpg: 18 HP
To me anyway, these numbers seem ballpark realistic. My previous Jeep pulling an interstate mountain pass with a trailer was getting fairly close to flat on the floor and 5 MPG. It was rated at 225 HP.
On another thread there's a discussion about rear differential temperature. Using the stated 4% mechanical loss in the differential and 746 Watts/HP puts the above numbers anywhere from 1.5 to 5.8 kW of heat being generated. No wonder the diff gets hot.
Some genius could probably come at it from the other direction - drag coefficient, rolling resistance, driveline losses. etc. That's way above my pay grade.
If someone has corrections or rebuttals on my math or info sources have at it - I'm plenty capable of making rookie errors
LF
Turns out fairly simple to figure - assuming I got it right anyway...
*** Nerd warning - proceed at caution ***
?
(or just skip to the numbers further down...)
Wikipedia has 'Gasoline Energy Equivalence' tables. They show a gasoline equivalent fuel energy (GEFE) of ~45 HP-Hrs / gal.
Another helpful Wikipedia table listed 'Brake Specific Fuel Consumption' data for a broad cross-section of engines, including both gasoline and diesel. This data measures the net crankshaft brake horsepower output per the amount of fuel consumed.
From this info a mechanical power output the efficiency can be determined (and is provided in the same Wikipedia table). Modern automotive gasoline engines ranged mostly in the low-mid 30% range, so I picked 33% as a ballpark efficiency value (EFF). A DI gas engine would be higher, and a diesel higher yet, but my engine is MPFI so that seemed reasonable.
Calculating gallons per hour consumed is easy: MPH/MPG = GPH
Not much harder is the net engine output horsepower: GPH * EFF * GEFE = HP
Or combined: MPH/MPG * EFF * GEFE = HP
somebody stop me, please ?
So plugging in some data to get engine output numbers...
Jeep down the highway at 60 mph and 17 mpg: 52 HP
Jeep down the highway at 75 mph and 13 mpg: 86 HP
Jeep pulling a camp trailer at 70 mph at 11 mpg: 95 HP
Jeep pulling a trailer up a grade at 65 mph at 5 mpg: 193 HP
Jeep on a rough trail at 10mph and 10mpg: 15 HP
and of course...
Prius zipping down the highway at 60 mph and 50 mpg: 18 HP
To me anyway, these numbers seem ballpark realistic. My previous Jeep pulling an interstate mountain pass with a trailer was getting fairly close to flat on the floor and 5 MPG. It was rated at 225 HP.
On another thread there's a discussion about rear differential temperature. Using the stated 4% mechanical loss in the differential and 746 Watts/HP puts the above numbers anywhere from 1.5 to 5.8 kW of heat being generated. No wonder the diff gets hot.
Some genius could probably come at it from the other direction - drag coefficient, rolling resistance, driveline losses. etc. That's way above my pay grade.
If someone has corrections or rebuttals on my math or info sources have at it - I'm plenty capable of making rookie errors
LF
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