RPM vs Speed - Ford Powerstroke Diesel Forum
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post #1 of 3 Old 10-30-2013, 06:29 AM Thread Starter
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RPM vs Speed

Hi All,
I have a 96 E-350 Van with a 3:55 rear, 4 speed automatic.
Unfortunately it does not come with a Tachometer, but I wish to correlate RPM vs Speed. Could someone with a Tach and the same rear give me a reliable engine rpm at a certain speed?
Any speed will do.
Why?
So I can make a chart giving fuel consumption vs rpm for our 210 hp @ 3000 rpm 7.3 engines, and post it here.
Sincere thanks in advance,
Dick
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post #2 of 3 Old 10-30-2013, 07:16 AM
over thinking everything
 
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PowerStroke Horsepower and Torque
Hp and torque dyno numbers

I like to keep the engine between 1800-2200 as that is where peak torque is, peak torque=peak mileage in my experience
if you have 245/7516 tires 2000 rpm is 71.95 at that speed aerodynamics come into effect and hurt mileage due to the fact tires are rarely their mathematical size and differences in tire diameter from manufacturer to manufacturer your speed at 2000 would be closer to 67.22. Again anything over 65 and aerodynamics hurt your mileage so 1800 rpm would realistically= 60.49. That is great for mileage but a bit slow and boring, however 1900 rpm again adjusted for reality would be 63.85mph. A bit better as far as boredom goes but still on the edge of ok for mpg.

All numbers were figured with the following formula

(Rpm x tire size)divided by (gear ratio x trans ratio x 336) = mph

I get bored and do this math while driving

97 F-250 CCSB 4x4 7.3 E40D 305,000 miles 285/75/16 Cooper Discoverer at3s' diy 6637 intake diamond eye 4in stainless turbo back straight pipe auto meter pyro, trans temp and boost gages on triple a pillar pod baby swamps and php hydra chip - paid off 335hp 704tq currently getting 12.5 mpg hwy


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post #3 of 3 Old 10-30-2013, 12:32 PM Thread Starter
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Quote:
Originally Posted by fordmandan87 View Post
PowerStroke Horsepower and Torque
Hp and torque dyno numbers

I like to keep the engine between 1800-2200 as that is where peak torque is, peak torque=peak mileage in my experience
if you have 245/7516 tires 2000 rpm is 71.95 at that speed aerodynamics come into effect and hurt mileage due to the fact tires are rarely their mathematical size and differences in tire diameter from manufacturer to manufacturer your speed at 2000 would be closer to 67.22. Again anything over 65 and aerodynamics hurt your mileage so 1800 rpm would realistically= 60.49. That is great for mileage but a bit slow and boring, however 1900 rpm again adjusted for reality would be 63.85mph. A bit better as far as boredom goes but still on the edge of ok for mpg.

All numbers were figured with the following formula

(Rpm x tire size)divided by (gear ratio x trans ratio x 336) = mph

I get bored and do this math while driving
Perfect!
Thanks Dan, I especially like the tire adjustment.
Dick
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