• Welcome Visitor! Please take a few seconds and Register for our forum. Even if you don't want to post, you can still 'Like' and react to posts.

MPH Vs. RPM

CopyKat

New Member
Joined
Aug 18, 2007
Messages
2,274
Reaction score
7
Points
0
Location
Manitoba, Coldest place in Canada
Vehicle Year
1987
Make / Model
Ford
Engine Size
4.0L
Transmission
Manual
In 5th gear doing 65 MPH my RPM is at about 2100. With the 4.10's and 33's I'm averaging 16.5 Mpg.

Best I got with 35's for 2 weeks was a 17 MPG. Best overall I've had is about 19.75. And that was Granny driving like no tomorrow.
 


Beanmachine7000

New Member
Joined
Jun 5, 2008
Messages
2,007
Reaction score
5
Points
0
Location
Tennessee
Vehicle Year
1991
Make / Model
Ford
Engine Size
4.0L
Transmission
Manual
Because when you drop the revs too much, the engine will instead be lugging (which also consumes more fuel, not to mention is brutal on the engine's bottom end).

Anything below 2200 RPM or so is very unlikely to save anything in fuel (2500 if you're cruising at interstate speeds).

Yes, Ford didn't do so well on gearing these trucks from the factory. Even stock, many are far from optimum (3.27s in a 4WD is a classic example). Even 3.73 is a tad tallish in many cases.
+1... The internal combustion engine is basically an air pump... The speed that you can move the most air, in the least amount of time will ALWAYS be the most efficient... 2400 rpm for the 4.0L OHV... Run it anywhere but there and you will get lesser efficiency... Running it too slow (ie 1500rpms) will waste fuel because more of it is turned into heat instead of making power... It CAN also be hard on internals because you are dealing with increased pressures inside the cylinder...
 

rmcnelly

New Member
Joined
Aug 21, 2008
Messages
19
Reaction score
2
Points
0
Location
Chesapeake, VA
Vehicle Year
2006
Make / Model
Ford
Engine Size
4.0
Transmission
Automatic
I can pull that off every once in a while, but it's rare and usually only for a minute. The problem I have is if I can even manage to get it into 5th and bring it back down to 40 mph, the slightest twitch of my foot on the pedal or the slightest hint of an uphill grade will make it downshift. For me, to consistently stay in 5th, I have to be doing at least 45. I've even tried playing with the cruise control, but that just makes matters worse when setting it at the 40-45 mph range. The OD develops a mind of it's own and just can't decide what it wants to do and stay there. At that speed its in a constant state of upshiftdownshiftupshiftdownshift......
Wow, mine isn't nearly that quick to downshift, but then again it is a stripper 2WD truck with the 4.0/Auto/3.55 gears/225/70-15 tires, and the engine isn't bogging at all.
 
Last edited:

kkjb4x4.0

New Member
Joined
Oct 2, 2007
Messages
185
Reaction score
1
Points
0
Location
Barrie Ontario Canada
Vehicle Year
1997
Make / Model
mazda
Transmission
Manual
Wow 18 to 20 mpg would be awesome, mine consistently averages 15 mpg no matter how I drive. 5 sp standard reg cab.
 

Viva*the*Ranger

New Member
Joined
Nov 1, 2008
Messages
2,108
Reaction score
43
Points
0
Location
Bellingham, Wa.
Vehicle Year
2003
Make / Model
Ford
Engine Size
4.0
Transmission
Automatic
Wow 18 to 20 mpg would be awesome, mine consistently averages 15 mpg no matter how I drive. 5 sp standard reg cab.
Word. I'm lucky if I get 17mpg on the highway. I'm about 14-15 through town. That’s with a 3.0 and 33's with 4-10's. I usually wind up turning my OD off to avoid lugging. Mine shifts to OD waaay too early. I’d be pretty happy if I were you with 20mpg.

-Chris
 

Jay FX4

New Member
Joined
May 13, 2009
Messages
3,819
Reaction score
25
Points
0
Location
Dearborn, MI - Home of the Blue Oval
Vehicle Year
2004
Make / Model
Ford
Engine Size
4.0L
Transmission
Automatic
I have gotten 21mpg a couple times too, all city. I don't go over 2500 rpm. I go somewhere between 2250-2500rpm in 1st and 2nd, and right around 2000 for 3rd and 4th. It's all about acceleration. I still go 5-10mph over the speed limit, but I just take my time getting up to speed. Not too shabby for a 4.0, 4.10's, and a slushbox.
 

Beanmachine7000

New Member
Joined
Jun 5, 2008
Messages
2,007
Reaction score
5
Points
0
Location
Tennessee
Vehicle Year
1991
Make / Model
Ford
Engine Size
4.0L
Transmission
Manual
It's not impossible to get 18-20 mpg out of the 4.0L... I do it consistently, closer to the 20 side if I keep out of stop and go traffic all the time... Just recently got 22 mpg on a camping trip... This was loaded will all the gear for 3 people for a week of camping... 55mph in 4th gear all the way netted me 22.3mpg average... I averaged 20 for the entire trip including some mild trail running and 2nd/3rd gear unimproved roads most of the time... Keeping my engine around the peak torque rpm is the key...
 

Sponsored Ad


Sponsored Ad

Top