M5od-r1hd

dclabo · Jun 8, 2016

Hey, folks. Long time listener, first time caller. Newbie to the manual transmission world. I have just acquired a 2003 Ranger XLT FX4 5 speed manual. When I'm running on the highway at 70-80 mph, the engine is turning 3000 rpm. This is eating up my fuel mileage (not that I expect superb mileage from a 4x4)...I get better mileage in town than I do on the open road. Is it possible to change 5th gear from a .79 to .5 ratio? Doing so would drop my rpm by close to 1000 rpm at "top speed."

Any advice or suggestions would be greatly appreciated.

alwaysFlOoReD · Jun 9, 2016

I've never heard of anyone doing so. Dropping rpms that low would lug the engine and potentially harm it. I think best rpm for mileage is where the BSFC [brake specific fuel consumption] is lowest, and that isn't at 1000 rpm on any gas engine I'm familiar with. What engine is in your truck?

Transman304 · Jun 9, 2016

Change the gear ratios of the diff.

dclabo · Jun 9, 2016

I don't want to drop rpm TO 1000. I want rpm @ 80mph to be around 2000-2200. Where is should be.

I have the 4.0 SOHC

Denisefwd93 · Jun 9, 2016

First check the door sticker for wheel & tire size

Tedybear · Jun 9, 2016

Denisefwd93 said:
First check the door sticker for wheel & tire size

This and I'd also peek at the diff tag and compare it to the axle code on the door sticker. At 65mph we've been running an average of 2250-2350RPM with our explorer. I know that's not quite the same, as you have the SOHC and we have the older push rod engine. Gearing will always play a role. Perhaps yours is a "Hauler" setup and not a "speed" setup. (as in, geared for the extra torque needed for hauling stuff, and not for zipping down the highway)

See what the axle code on the door sticker states, and compare it to the axle tag on the diff. It's always possible it got changed out.

Also need to understand (and I'm not trying to be rude....so don't take it that way) The faster you push the truck speed-wise.. The worse the mile per gallon will be. We're not talking about a super aerodynamic sports car.

Throttle things back to 65 top speed for a tank of gas and see what the MPG is. Then compare to 80 on a tank of gas. It might be interesting to compare.

S-

Denisefwd93 · Jun 9, 2016

My truck with the right size tires 265 15 75 still has an a4ld and gets around 2- 2200 RPM at turnpike speeds. like 60-75 speedo is close to right now also. the small tires that were on it. 255 I think they were.. were a much smaller diameter. Good highway mileage bad around town.

4x4junkie · Jun 9, 2016

Tedybear said:
Also need to understand (and I'm not trying to be rude....so don't take it that way) The faster you push the truck speed-wise.. The worse the mile per gallon will be. We're not talking about a super aerodynamic sports car.

Throttle things back to 65 top speed for a tank of gas and see what the MPG is. Then compare to 80 on a tank of gas. It might be interesting to compare.

S-

×2
Slowing down to 60-65 will increase your mileage probably 10-fold the amount any changing of gear ratios can...

Why be in such a hurry?

alwaysFlOoReD · Jun 9, 2016

dclabo said:
i don't want to drop rpm to 1000.

oops....

bobbywalter · Jun 9, 2016

4x4junkie said:
×2
Slowing down to 60-65 will increase your mileage probably 10-fold the amount any changing of gear ratios can...

Why be in such a hurry?

if your working 13 hrs a day......driving 3 hrs a day from room/camp to worksite and back.....and 800 miles to that 3 hrs a day work area, and 800 miles back for days off.....80 mph is not fast enough.....so 80 dont seem like much of a hurry. not sure if its this guys case...but it is mine.

what i would need to know is current gear and tire size....is it lifted? what is the road weight? is it covered in off road lights and antennas...???...

shit like that.

bobbywalter · Jun 9, 2016

dclabo said:
I don't want to drop rpm TO 1000. I want rpm @ 80mph to be around 2000-2200. Where is should be.

I have the 4.0 SOHC

2200 at 80 mph.... is where it should be? :shok:

a 4.0 gasoline powered engine? or did you swap a powerstroke or something in there?

because the idea of that is patently ridiculous. that cammer engine is made to get its best mpg at higher rpms then that with a much lower wind load.

RonD · Jun 9, 2016

You would have a 4.10 axle ratio if RPMs were 3,000(2,900+) at 80mph in 5th(OD)

FX4 probably has 30"-31" stock tires, and you only lose about 100rpms per inch on larger tires.

Switching to 3.73 ring and pinion would put RPMs at 2,600 at 80mph
2,300rpm at 70mph

dclabo · Jun 9, 2016

All helpful info, well accept for being called patently ridiculous. Can't for the life of me figure out why help can't be offered without insult. But I digress...

Not in a hurry, per se. Speed limit is 70, just getting a tad beyond that. Yes, door jam says I should have 4.10 rear end. 31.5" tires...door claims 245's are stock rather than the 265's it came with.

If this is normal, forgive my ignorance. That's why I ask questions...to cure ignorance via accumulation of knowledge. I was basing my judgment on the fact that my 5.7 Vortec tooled along at 80mph pushing a mere 2200 rpm. Maybe this little 4.0 should run higher. I was unaware of that.

4.10
265 75 16 tires

Thanks, I think.

dclabo · Jun 9, 2016

bobbywalter said:
if your working 13 hrs a day......driving 3 hrs a day from room/camp to worksite and back.....and 800 miles to that 3 hrs a day work area, and 800 miles back for days off.....80 mph is not fast enough.....so 80 dont seem like much of a hurry. not sure if its this guys case...but it is mine.

what i would need to know is current gear and tire size....is it lifted? what is the road weight? is it covered in off road lights and antennas...???...

shit like that.

Not lifted
4.10
265 75 16
No extras (lights, antennas, brush guard, winch etc)
My scale doesn't read that high ? (seriously, not sure I'd have to check the door)

RonD · Jun 10, 2016

4.10 is for towing and general "peppiness" for around town driving or off-roading.

Your 5.7l vehicle most likely had 3.50 or less, axle ratio.

RPMs are RPMs, engine size doesn't matter, but torque and horse power do to some extent.
Having extra power from a V8 means you can drop the axle ratio down more to get higher top speed and still retain some "peppines" for around town.

Most Rangers came with 3.73 regardless of engine size, FX4 often came with 4.10, I think it was part of that package.

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