Best RPM for MPG?

[Frak]

I have read a few threads about keeping the TDC above 1700-1800 rpm for optimal running performanc. Is it allright to drop down to 1000-1500? this is where you get best mph. So what I am asking is whats the best rpm to run empty and w/load. I'm wondering if the 1700-1800 I read about was for towing?

 

[SRadke]

You'll see your best mileage from 1700-1800 rpm. On most trucks this falls in around 50-55 mph where you're moving along but areodynamic drag is still minimal.



-Scott

 

[mconstable]

I notice a pretty big loss in MPG if I spend too much time near or above 2,000 RPM's, if I stay below 1,900 RPM's, I can get over 20 MPG on the highway all day long... above 2,000 it can drop to 16 or 17 real quick.

Hope this helps!

 

[CajunDieselMan]

I run about 2300-2500 rpm (70-75 mph) on the interstate and get about 20MPG. I can imagine what I'd get if I kept it to 55-60 MPH.

 

[Frak]

Mpg

I have only 4700 miles, and it seems to get much better mpg if I run arround 1500-1700 in town. Is it bad for the engine to run low RPM? On the highways and such I run around 2000 and up (depending on how fast I'm going) and get between 15-17, this should get better with more miles? Right? I know it will be better with air intake, exaust, and chip, but it should get a little better stock,

 

[SRadke]

Above 2000 rpm on the highway I wouldn't EXPECT better than 17. It is possible and it's great if you have a truck that will do it but to expect it from an 8000 pound 4x4 is asking a lot IMO. And yes, your mileage should pick up with some more miles but don't expect miracles.



-Scott

 

[mattymac]

Below 2k and under 10lbs of boost is where youll get your best MPG. At 67mph I am at 2000 and about 10-10. 5 lbs of boost is always where I get my best MPG per MPH. Its hard to run any slower than for me if im trying to cover some interstate.

 

[gsbrockman]

At one time another member posted here that the 325/600's don't shut off the 3rd injection event until 2,000 rpm so I'd bet the 325/600's will do best after 2,000 rpm. Any 325/600 guys or gals remember the post ?

Greg

 

[JVolpe]

I have an 04. 5 325/600. My mileage has never been great, but ok for my driving conditions. I now average about 14mpg all stop and go city rush hour traffic. About 16. 5-17mpg highway and that is at 75-80mph. With 3. 73 gear and 315s 2000rpm=78mph. That is usually where I set the cruise control. I rarely drive over 2000rpm for very long. Maybe I need to kick it up to 2100rpm on cruise. Thats about 83-84mph, I could get away with that in Texas, 75mph will get you passed in the slow lane normally.

 

[Buffalo]

I recently returned from May Madness, in Las Vegas, where I sat in on a seminar by Mr. Dennis Hurst from the Cummins Engine Co. He is the Head Engineer (I believe) and is referred to as the "Father of the 3rd Gen. Engine". This question was asked of him and his response was that the "sweet-spot" is in the 1800-1900 rpm. range.



However, some of us have noticed that the 2100 rpm. range seems to provide good fuel mileage.



Hope this helps.



By the way, Mr. Hurst's talk was extremely interesting. Dodge even sent a "cut-away" of the 3rd. Gen. HPCR engine, at a cost of $2800. 00 in shipping charges. That engine was beautiful!!!



If you ever get a chance to go to May Madness, you won't regret it. The seminars are extremely interesting and they bring in a lot of the top people in the industry. Can't do much better than being able to talk to the head guy in charge of the building of our engines.



Joe F. (Buffalo)

 

[XJSuperman]

I do a LOT of stop and go driving (IE taking 30 minutes to go 6 miles) and a fair bit of hwy miles weekly as well. With that said I keep mine between 1800-2200 RPM almost all the time... with no real comparison for the difference between that range. I also run the RPMs up a fair bit when taking off... meaning I see redline frequently... not always but often.



I get a hand calculated (over MANY tanks) 17 city and have seen on 2 separate hwy trips 22 MPG. This is all empty... but I don't baby the truck. I usually have a near 50/50 split city/hwy and get an avg of 19 MPG... sometimes I see in the high 18's... others in the high 19's.

This is an '04 305/555 6 spd with EZ on 4, AFE intake, and 4" exhaust (3. 5" downpipe still).



I think a lot of differences are seen #1) because the 600's and 610's don;t get as good as the 555 motors in fuel mileage.



#2) I think a lot of folks try to lug these motors... sure it doesn;t hurt the motor... but it doesn;t help fuel mileage either... I think I read somewhere here where cummins has stated clearly that these motors are most efficient NOT only at the magic 10/600 numbers for boost/EGT repsectively BUT also at 1900-2200 RPM's. ( I think I read that here)... and by lugging I read somewhere that someone puts there 6 spd into 6th gear by 30 MPH... I think that;s silly personally. Just because an engine makes its peak TQ and/or HP at a certain RPM doesn't mean it's most efficient at the same RPM. It seems enough folks have purposely run at lower RPM and run at higher RPM to try and see fuel mileage differences and there really aren;t any.



#3) because so many of us live in different climates... I'm in FLorida so elevation is RARELY a concern of mine for EGT's... and at 70 MPH at 2000-2100 RPM's I;m sitting at about 500* EGT... and based on my previous truck (I have no boost guauge yet in this one) I;m at about 8 lbs or so of boost... so again that all falls into the magic numbers set by cummins... so it's tough for us to all compare MPG when we don;t live near one another.

 

[HParfitt]

Hi,

I think gsbrockman has something with running at 2000 and highter rpm and the 3rd injection event. I found that running at slower speeds where aerodynamic drag doesn't play into it as much running 2100 - 2300 provides the best mileage. On country 2 lanes I've been running in 5th instead of 6th, I'm seeing 17-18mpg empty my boost is around 10psi and egt's post turbo around 500F. When your on the highway in 6th at those engine speeds 70mphish I think aerodynamic drag becomes greater than possible combustion efficiencies. I have noticed on level ground at say 50mph shifting to 6th and the resultant drop in engine rpm causes egt's to rise. Has anyone confirmed the 3rd injection event shuts off at 2000 rpm. Could the new flash be shutting off the 3rd injection event at a lower rpm? Anybody do any research into disabling the 3rd event? Accounting for my dumb questions. I'm new and not nearly as knowledgeable as most people here.

 

[tae73]

ZERO rpms is the best milage saver! Oo. Oo.

 

[J&LRam]

my '03 has 46000 mi and is driven 110 mi a day work commute. It runs 20. 5 to 21. 5 tank after tank , month after month. Milage won't vary any wheather I'm running 75 mph on the turnpike or 55-60 mph on old highway 66. This truck gets 12-13 towing 11200 lb 5er. Running empty I shift around 2000 rpm and towing I shift at about 2500-2600 rpm. I don't have a town for city milage. All pencil figures... ... ..... JIM

 

[DocDetonancour]

70 to 75 mph = 20+ mpg. Doc