ETH - Best MPG is at 1850-2000 RPM

[Archive]

Dane... Congrats on finding your sweet spot, but Your info was a little wrong. Cummins, and my Power Boosters newsletter has said for several years that the "economy" range for the 24 valve is 1800-2000rpms. The "power" band is 2000-2250. This may have even been in a past TDR issue.

The high rpm thing is not for power or economy, as I understand it, is merely a statement that the 24 valve can withstand high rpms for a sustained time.

Disclaimer: I have no idea what your eth is, but doubt it would change much.
I will search thru my old TDR mags for this info!

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Rob Hanson
1999 "Big Red", 3500 SLT QC 4X4 6 spd, 4. 10 LSD, Braided SS fuel lines, Mag-Hytec Rear Cover, Cummins E-Brake, Blue Box, DD3 Injectors, Banks High Ram and 14cm Wastegated Turbo, All-steel Cowl Induction Hood, Cummins RED Valve Cover, Rhino, Rosewood Kit, Scotty System, SportComp Gauges, TorkLift SuperHitch, Tekonsha Brake Controller, Rear Flood lights, Cobra CB, DeeZee Running Boards, BD 2WD Low kit, Air Lift bags and a Geno's "I tromped a Ford" decal. Member of BOMB! (WW NW Chapter)

MyPics.com (pics updated 10/14/00)

I'd rather be... .
Cummin than Strokin.

 

[Crazy Horse]

My MPG "sweet spot" has also been between 1800-2000 RPM's. The power "sweet spot" has been 2000-2300 RPM's. My observation comes from recently driving from Alaska to South Carolina with 3600 lb camper in the bed, and towing an 1800 lb trailer behind. As soon as I start pushing it over 2000 RPM's it's a fact,LOWER MPG's FOLLOW. The same seems to be true down here unloaded so far. #ad


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2K Dodge 3500,4x4,SLT,Quad Cab,PR4 Red,Auto Trans,3. 54's,Anti-Spin Axle,Trailer TowPack,3 Piece Auto Ventshade Hood Protector,"BEEFED" up Factory Camper Pack{No Airbags},Factory Fogs,Rear Slider,Rancho 9000's,Rhino Spray In Liner,Smitty Built Nerf Bars,Alpine 60x4 Watt CD Player,Lance Cabover Camper,BD Plug n Power,K&N w/Modifed Stock Box,Amsoil 15w40,EGT Guage,And Enjoying The Ride.

2K Dodge 2500 SLT RC LB PB3 Blue
99 Dodge 1500 SLT/Sport RC SB Solor Yellow {Her Truck}

 

[Vaughn MacKenzie]

Dane, how far south did you drive? Was diesel expensive? In June 1992 we drove to Bahia de Los Angeles and unleaded was around $1. 40 to $1. 50 a gallon (much higher than in California at that time). We found everthing to be expensive, much to our dismay. The roads were not too bad, except the one to L. A. bay was an axle buster.

The scenery is quite interesting and I would enjoy a trip to Baja again. It really gets remote once the highway heads east away from the Pacific. But when I ever do get down to Mexico again, it will be to ride the Copper Canyon railroad from Los Mochis to Chihihuahua.

Vaughn

 

[Dane]

Hey Guys, Happy New Year! Just got back from a 2000 mile round trip to Baja. I was able to do some best RPM/Fuel mileage tests. The last jump to my final destination required a 360 mile black top + 30 miles off road round trip. This was WAY out in the middle of nowhere so I had to be correct in my fuel requirement calculations. I found the "sweet spot" on the ETH motor is 1850-2000 rpm. I know what Cummins says about the 24 valve liking higher RPMs, but that is NOT TRUE. I got 15 mpg with 2000 lbs of camper and supplys running this way. At 2200 rpms my MPG dropped to 13. 5 MPG. I am real sure that wind resistance is a factor on the highway, but off road 2200 RPM is too high unless your trying to get over stuff, running in sand or climbing a hill. The 6 speed was great! Always able to up or down shift to keep it in the sweet spot. A note of caution - When trying to run this way you're very close to lugging the motor/drive train in the higher gears, so you have to pay attention. I found listening to the engine/turbo music #ad
made it easy to keep it in the right RPM once I got used to running at that speed. With 3. 54 rear gear and 285s it was 60MPH in 6th and 50MPH in 5th. Hope you all had a fun holidays #ad


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2001 HO 6 speed Regular Cab SLT 4x4 3. 54 anti spin 2500. Used for the daily grind and sneaking away to some secret Baja beaches toting a cabover

 

[Posm]

When Cummins tells us that the ISB operates most effecintly in a certain RPM range they are controling the variables. They are using a constant load. I would like to see some wind tunnel data on the mighty Ram. I suspect the load is 50% greater to push my 2500 4 X 4 at 80 than at 65. Even if the engine is more eficient at a higher range it would not make up for the increased load.

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Y2K 2500, QC, 4X4, 3. 54LS, ST, 5 speed, SWB, 12 Disk JVC CD

 

[HC]

Even if the engine is more efficient at a higher range it would not make up for the increased load.

Posm,
I'm with you on this one. The slower I go, the better my mpg gets, provided I don't end up in 4th or lower gears. In fact, this morning on a level stretch, I even noted
that at a constant 45 mph, the trip computer showed better mpg at 1250 rpm in 6th than it did at 1750 rpm in 5th. In addition to the wind resistance you mentioned, I'm convinced that all the charts folks have reviewed to come up with the "efficiency" range are based on full-load conditions. I don't believe that the engine curves at a fixed light load (like exactly the Hp required to push me down the road at 45 mph) would show exactly the same rpm/efficiency relationships, otherwise my mpg should have gone up when I dropped in to 5th gear.

P. S. - No, I'm not going to drive at 1250 rpm for more than a few minutes, just to do this test! Great mpg isn't worth shortening the engine/drivetrain life.