2100 rpm's at 75mph--is that normal?
#1
11-24-2004, 10:33 AM
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2100 rpm's at 75mph--is that normal?
Just got my first diesel truck...05 F250 CC 4WD SB....When I'm cruising on the freeway at 75 mph the rpm's are up around 2100.....Is that normal???? Maybe I'm just not used to the sound of a diesel...it sounds like it's running high to me....Is that normal rpm's for that speed????
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11-24-2004, 11:23 AM
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Yep - normal and I assume you have 3.73 gears. I have an 05 and with the 3.73 gears and the new 5 speed auto, 70 MPH is just around 1850 RPM (used to be 2000 RPM for 70 with the old 4 speed tranny)...
Also, my truck is super quite at those speeds - can't hardly hear the motor. And remember, these new diesels rev MUCH higher - mine's stock and I've had it around 4300 RPM and it just LOVES it.....
Also, my truck is super quite at those speeds - can't hardly hear the motor. And remember, these new diesels rev MUCH higher - mine's stock and I've had it around 4300 RPM and it just LOVES it.....
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11-24-2004, 11:52 AM
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RPM = (MPH x GR x RE x 1056) / (TireDia x Pi).
For the Torqshift the gear ratio in OD is 0.712 and the normal rear end ratio is 3.73. The tire diameter is 31.65 inches. So 75 MPH equals 2115.392 RPM.
You can always simplify the equation a bit by dividing 1056 by Pi and come up with:
RPM = (MPH x gr x re x 336.135...) / TireDia.
TireDia by the way can be calculated by ((2 x TW x SW) / 25.4) + RimDia
If you had the stock 265/75R16 tires then plug the numbers in as:
TireDia = ((2 x 265 x .75) / 25.4) + 16 = 31.65 inches.
Of course the actual rolling diameter is dependent on load and tire inflation. To really check that, you can chalk the side of the tire where it meets the ground and and then chalk the ground and roll forward some number of turns and measure the distance and then find the average distance per turn and divide by Pi and Bob's your uncle . . .
Our motto: "Engineers, making easy things hard for the average guy . . ."
For the Torqshift the gear ratio in OD is 0.712 and the normal rear end ratio is 3.73. The tire diameter is 31.65 inches. So 75 MPH equals 2115.392 RPM.
You can always simplify the equation a bit by dividing 1056 by Pi and come up with:
RPM = (MPH x gr x re x 336.135...) / TireDia.
TireDia by the way can be calculated by ((2 x TW x SW) / 25.4) + RimDia
If you had the stock 265/75R16 tires then plug the numbers in as:
TireDia = ((2 x 265 x .75) / 25.4) + 16 = 31.65 inches.
Of course the actual rolling diameter is dependent on load and tire inflation. To really check that, you can chalk the side of the tire where it meets the ground and and then chalk the ground and roll forward some number of turns and measure the distance and then find the average distance per turn and divide by Pi and Bob's your uncle . . .
Our motto: "Engineers, making easy things hard for the average guy . . .
"
#6
11-24-2004, 12:14 PM
Originally Posted by darylhunter
RPM = (MPH x GR x RE x 1056) / (TireDia x Pi).
For the Torqshift the gear ratio in OD is 0.712 and the normal rear end ratio is 3.73. The tire diameter is 31.65 inches. So 75 MPH equals 2115.392 RPM.
You can always simplify the equation a bit by dividing 1056 by Pi and come up with:
RPM = (MPH x gr x re x 336.135...) / TireDia.
TireDia by the way can be calculated by ((2 x TW x SW) / 25.4) + RimDia
If you had the stock 265/75R16 tires then plug the numbers in as:
TireDia = ((2 x 265 x .75) / 25.4) + 16 = 31.65 inches.
Of course the actual rolling diameter is dependent on load and tire inflation. To really check that, you can chalk the side of the tire where it meets the ground and and then chalk the ground and roll forward some number of turns and measure the distance and then find the average distance per turn and divide by Pi and Bob's your uncle . . .
Our motto: "Engineers, making easy things hard for the average guy . . ."
For the Torqshift the gear ratio in OD is 0.712 and the normal rear end ratio is 3.73. The tire diameter is 31.65 inches. So 75 MPH equals 2115.392 RPM.
You can always simplify the equation a bit by dividing 1056 by Pi and come up with:
RPM = (MPH x gr x re x 336.135...) / TireDia.
TireDia by the way can be calculated by ((2 x TW x SW) / 25.4) + RimDia
If you had the stock 265/75R16 tires then plug the numbers in as:
TireDia = ((2 x 265 x .75) / 25.4) + 16 = 31.65 inches.
Of course the actual rolling diameter is dependent on load and tire inflation. To really check that, you can chalk the side of the tire where it meets the ground and and then chalk the ground and roll forward some number of turns and measure the distance and then find the average distance per turn and divide by Pi and Bob's your uncle . . .
Our motto: "Engineers, making easy things hard for the average guy . . .
"
, EJ
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11-24-2004, 01:01 PM
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11-24-2004, 02:49 PM
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11-24-2004, 04:49 PM
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11-24-2004, 07:10 PM
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I love that Engineering motto! I am a Chemical Engineer by trade myself, so Engineer humor is well appreciated here in cowboyland as well.
Yeah, the 2100 revs is fine for this motor. The governor is at 4000 revs, FYI. This motor has a lot of nifty innovations in it, such as a new crankshaft casting procedure, that enable higher revs. The reduced displacement and better metals technology also helps reduce piston mass, which leads to higher revs being possible. I've had mine hammer away like that for days at a time, and she seems to take it in stride. This is actually my first diesel truck as well, and I have embraced it with a passion. I have had exposure to industrial diesels and, of course, my tractor. That can only rev to 2750.
Yeah, the 2100 revs is fine for this motor. The governor is at 4000 revs, FYI. This motor has a lot of nifty innovations in it, such as a new crankshaft casting procedure, that enable higher revs. The reduced displacement and better metals technology also helps reduce piston mass, which leads to higher revs being possible. I've had mine hammer away like that for days at a time, and she seems to take it in stride. This is actually my first diesel truck as well, and I have embraced it with a passion. I have had exposure to industrial diesels and, of course, my tractor. That can only rev to 2750.
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#15
11-28-2004, 02:44 PM
Originally Posted by superv10
Yep - normal and I assume you have 3.73 gears. I have an 05 and with the 3.73 gears and the new 5 speed auto, 70 MPH is just around 1850 RPM (used to be 2000 RPM for 70 with the old 4 speed tranny)...
Also, my truck is super quite at those speeds - can't hardly hear the motor. And remember, these new diesels rev MUCH higher - mine's stock and I've had it around 4300 RPM and it just LOVES it.....
Also, my truck is super quite at those speeds - can't hardly hear the motor. And remember, these new diesels rev MUCH higher - mine's stock and I've had it around 4300 RPM and it just LOVES it.....
Is your truck two wheel drive?