Best rpm for mpg?

[WBacon]

I know this is a broad question but... . 06' CC DRW 48RE 4. 10. Empty on flatish ground what is the most efficient rpm for the cummins to run on the highway?

 

[Bertram65]

I have the same combo, I have never noticed any significant difference in mpg on the highway. I have run whole tanks without going over 2000rpm, and whole tanks running 2500rpm, and everything in between, always get around 16 to 16. 5 with summer fuel and about 1mpg less with winter fuel, all hand calculated no mpg computer on my truck.

 

[WBacon]

I'd be happy with that. Your signature says SRW though!

 

[cerberusiam]

The sweet spot is 1950 rpm's. Any more than 2000 rpm's and the mileage will drop. Anything less than 1800 rpm's the same. Economy is 1900 to 2000, power is 2400 to 2500. They ARE mutually exclusive. My 05 SRW QC auto 3. 73 will run 19 to 21 mpg year round at 1950 rpm's. At 2100+ rpm's it will be 15 to 18 depending on the weather, fuel. I run PS/MMO every tank.



You have about the worst configuration for mileage there is, aside from adding 4x4. The only thing you can do is keep the rpm's down and run high quality fuel. Great in theory, not so in paractice.



Bertram65 also has an 03. Different animal than the 600/610 motors.

 

[WBacon]

Mine is 4x4. I figure I would be happy at 14

99. 5 powerstroke CC SRW 4x4 14

01 dmax ally CC DRW 4x4 hi 14

03 cummins CC DRW 4x4 low 13

04 4500 CC 14' box 4x2 oh my god 8-9

06 cummins CC DRW 4x4 already in the 12s with 1500 miles so I have hi hopes.

I think my speed maybe a problem All the pickups had low gears by the way.

 

[WBacon]

What is PS/mmo?

 

[DwayneKelch]

WBacon,



PS = Diesel Power Service. MMO = Marvel Mystery Oil

 

[Bertram65]

I'd be happy with that. Your signature says SRW though!

True, I was referring to the 4. 10s and automatic, though mine is an '03 and yours and '06 they may get different mileage overall, but I was referring to rpms and different mileage and what I have seen, which is very little difference.

 

[lgjohnson]

The sweet spot is 1950 rpm's. Any more than 2000 rpm's and the mileage will drop. Anything less than 1800 rpm's the same. Economy is 1900 to 2000, power is 2400 to 2500. They ARE mutually exclusive. My 05 SRW QC auto 3. 73 will run 19 to 21 mpg year round at 1950 rpm's. At 2100+ rpm's it will be 15 to 18 depending on the weather, fuel. I run PS/MMO every tank... .

I have an '03 3500 SRW, 48RE, 2WD and I'm seeing and experiencing the same thing. I have almost 60,000 miles on her now. I also use 4oz MMO and 8 oz PS on each fill up... ...

 

[BHolm]

There is a substantial difference between the 305 and 325 engines. My '03 would run 90 mph and get 18 mpg. It would run 70 and get 22. Both of my 325 trucks dropped off in milage much more quickly as speed/rpm increased. My combo is different than yours but from an rpm standpoint I have found milage to be very similar between 1800-2100 rpm. Once I go over about 2100 I start giving up 2mpg per 5 mph. Running over 80 with 3. 73s starts getting expensive.

 

[WBacon]

Thanks guys. I already see a difference between the 03 and 06. I think the 06 is better but the 03 had the tst and ats trans so I always did 80. Trying to do 65 is actually really hard but it seems to have a noticable difference.

 

[klenger]

I agree that doing 65 is pretty hard. I almost never break 60 myself.



For anyone that is complaining about the milage of a 7000 lb full size truck at 90 MPH, ... get a life.

 

[WhiteSheep]

It's the wind

65 MPH is sweet on my truck too. I suspect it is the wind resistance and not the RPM, however. As pretty as they are, our trucks have a BIG frontal area. Heck, the towing mirrors alone have nearly the frontal area of a Honda Civic.

 

[betterthanstock]

Try driving in direct (non-overdrive) which is 3rd locked-up for autos, and 5th for manuals at about 1400-1500 rpm (33-40 mph, speed will depend on your gearing and tires). I don't know if you can keep the TC locked up, maybe use tow-haul.



That's your truck's best possible mpg.

Your mileage will be 25-30+ mpg on flat ground with no wind if the engine is warmed up, on summer fuel.

 

[dodgestang]

Bacon, with my truck... 05 Dually, 8 foot bed, 4x4, quad cab with the 48RE and 4. 10 driving on the freeway at 68 MPH I get between 20-21 MPG according to the overhead... so that means its actually 18



Anyway, I run a SP Deisel box, cheapy NAPA large cone filter in place of the air box, 4 inch duals and I get my peak MPG at 2100 RPMs now. Stock it was 1900-1950 ish. When I drive all out 75-80 MPH with bursts to redline at various merging points I get 15-16 according to the overhead which is really more like 13-14.



I find that if I park it at 2k from a dead stop and let it run up through the gears I get the best overall mileage as apposed to light footing it and letting the RPMSs creep up or have the tranns shift at 15-1600 RPM.

 

[TowPro]

I bet it has more to do with airodynamics and speed then it does with RPM.



in my 02 I can run in OD lockout at 45 and get 2-3 more MPg then running with OD on at the same RPM

 

[WBacon]

When I said that I have trouble going 65 I meant I am usually going 75 . Dodgestang I pray that I can acheive those #s.

 

[Pawpaw]

Heck, the towing mirrors alone have nearly the frontal area of a Honda Civic.

That's funny! You're not wrong, though. :-laf



Bob

 

[Hohn]

The sweet spot is 1950 rpm's. Any more than 2000 rpm's and the mileage will drop. Anything less than 1800 rpm's the same. Economy is 1900 to 2000, power is 2400 to 2500. They ARE mutually exclusive. My 05 SRW QC auto 3. 73 will run 19 to 21 mpg year round at 1950 rpm's. At 2100+ rpm's it will be 15 to 18 depending on the weather, fuel. I run PS/MMO every tank.



You have about the worst configuration for mileage there is, aside from adding 4x4. The only thing you can do is keep the rpm's down and run high quality fuel. Great in theory, not so in paractice.



Bertram65 also has an 03. Different animal than the 600/610 motors.

Actually, the sweet spot is 1958 RPM. DO NOT GO 1960 RPM or 1950 RPM or your mileage will suffer!



On my truck, I noticed a solid . 00003 mpg increase running at the sweet spot.



J/K



Seriously, best BFSC for most 24V is exactly 2000 rpm. I've seen the certification sheet showing this (it was reproduced in the TDR rag a couple issues back for each series of engine).



The problem is that you CANNOT compare one RPM to another for mpg and conclude that any change is simply due to the different efficiency at a different RPM.



The fact is, EVERY SINGLE ONE of these trucks will get better mpg at 65mph than at 75mph. True, the engine may be more efficient at making HP at a couple hundred rpms more, BUT it's being asked to make a lot more hp to sustain 75mph vs 65 mph. That more than offsets any increase in efficiency.



In fact, there are cases where 4. 10 will actually get BETTER mpg than the taller gears (3. 73 or 3. 54 depending on truck generation).



But not many people want to drive 50mph to get the better mpg from the 4. 10s.



jh

 

[Donn]

I recieve a news letter from cummins I think around one every three months. In one of the emails they said that for best milage and performance to keep the egt under 600, and the boost under 10 lbs. It seems to work for my truck.