You are much better locking out OD than trying to tow in OD at those speeds. Under 1800 rpm's you wil gain very little if any in mileage plus it is extremely harder on the engine and transmission at those rpms.

TQ peaks around 2500 on most of the CR engines and they will run all day at those rpm's with decent efficiency. Drop to drive and run at the traffic speed. Its a lot safer and easier on the equipment.

 

I was out today and my rpm's at 50-55 mph are actually at 1300 rpm's and man I tell ya, the truck just doesnt seem happy pulling in that range. It just doesnt feel or sound right. Thats in overdrive. With overdrive off, of course the rpm's go to about 2200, but the truck is alot happier.

Thanks everyone for your responses, I'm just gonna pull with O/D off and go with that.

 

For what it's worth, I sent a question to Cummins on their website when I got mine. They defined lugging as running a load on the engine below 1600 RPM, or pulling a grade in a gear so high that the truck will not accelerate when floored.

 

I don't know if this helps, but the most I've towed with my truck is about 6K. Going up a slight grade (maybe 3%), I was able to be in 6th gear at 45mph. And it had plenty of passing power. It didn't seem to be lugging at all. Just a little more whistle from the turbo. On flats, and when empty, I will run in 6th gear at 30MPH. It's right about 1k RPM. Super quiet and barely any throttle .

 

You know, if I had it to do all over again, I would go with the 6-speed. The main reason I didn't was because of the old lady, but she has yet to drive the truck. Oh well I'll just learn to live with it.

 

That's exactly why I went with the auto tranny. On long trips she does drive, and it's a lot better for our marriage with the auto!

 

MY wife hates the 6speed! But she really likes the truck. If I had to do it all over again, I would have gone for an auto with 3.73 gears. I never tow, and I can't shift fast enough to beat a city bus in a race!

 

My wife was ****** off enough when I told her that I was trading in my '04 furd(because it was nothing but troubles, and only two years old). It would have really set her off if I got the 6-speed...you gotta know just how far you can go and compromise.

 

Yes! while towing I always start off with the OD turned off and usually I take in mind my terrian I'm in, once I get up to 50 or 55 or even 60 mph I'll push the button and turn it back on. Now if your on a two lane hwy some where and it is a constant slowing down speed up deal due to traffic I'll run OD off usually. My truck at 42 to 44 mph it will shift into OD and my RPM right before maybe 1800 or 1900 and then drops to 1300. Lot of times going througha town speed limit is 40 to 45 mph so I usually elect to turn off OD with the button. Your set up with the 07 having both T/H and OD off I'm not real familar with it. I have not drove a truck with both features or even read up on how they work together. The button is there for you as owners manual states if you encounter the constant shifting back in fourth from OD to drive go ahead and select the OD off button and this puts it in direct drive. Again as others stated also running in OD off will not hurt a thing either than some mileage may suffer. When I first started pulling my TT all I would use was the OD off I wanted to give the engine a work out too running in a higher RPM. I believe on your stock tranmission if you had a good set of gauges to keep a eye on temperture and keep the service done on it regularly (every 30K for me) and don't put yourself in a situation where your ******* the heck out of it (like getting stuck in a mud hole and trying to get out) and sticking a lot of HP in front of it, it will last you a long time. Some of the guy's on here go for the high HP with box's and downloaders and that's but sooner or a little later that trans will have to be beefed up a little more to compensate for that added HP .


Tony

 

The torque curve rises sharply to peak torque maximum starting at 1600 rpm and stays flat out to 2800 rpm before it starts to decrease. Peak torque is not just at 2500 rpm where you are almost finished the power band. Torque only stresses engine components when they are straining against an excessively heavy load. Pulling a load at 1300 rpm on a flat hard road will not hurt the engine or automatic transmission provided the exhaust gas temperature before the turbocharger is not too high to melt the aluminum engine pistons. If the slow turning engine suddenly has to labor hard then you can down shift a manual tranny or the automatic will down shift itself. I never had an automatic tranny with an I-6 diesel truck engine, but I assume the tranny would downshift while in OD if the pull became hard. I-6 truck engines do not need to be babied like V8 gasoline or diesel engines that need to run fast or they will stall out. If you ever operated a tractor with a 9.5 L I-6 Cummins you would feel how hard those engines can strain without hurting themselves.

 

While TQ may start at 1600 rpms, it peaks at 2400-2500 rpms and HP peaks at 3000 rpms, at least on the auto trucks. That 2500 is pretty much right in the middle of the power curve, which incidently is about where a G56 3.73 truck runs at 75 mph. The Cummins B has always been rated 100% duty cycle at 78-80% of governed rpm. Auto or manual, that puts it at 2200 to 2500 rpms at road speeds. Gear it down and raise the rpms when speeds drop. Any competent Cummins tech will tell you towing under 1800 rpm's is not recommended.

There are a couple reasons you analogy fails in the real world. Theory aside, the engine simply won't pull at the rpms you suggest. It will either loose speed or downshift to get the r's up. Under 1800 rpms the fuel curve ramps down quite quickly to less than 50%. Drop the fuel and the boost drops and it defuels more. A stock tune is a total dog at 1300 rpms and it simply will not pull.

Second, at 1600 to 1900 you are dead in the middle of the torsional harmonics of this engine. All you are doing is needlessly wearing thrust bearings, hammering the beejeezus out of the transmission and lugging it into and early demise. Not to mention auto trans pressures are extremly low at this point and under a load are very likely to be slipping clutches all the way thru the transmission. Manuals are not as bad but it is still not doing the equipment any favors.

Your analogy of a tractor is totally worthless in what we are dealing with in a road truck. There is a huge difference in a final drive in a tractor and these trucks. There is also a big difference in functional operating ranges between a 9.5 L and a 5.9 L. What may work in a tractor or industrial application is not the same as .69 OD and a 3.73 geared final drive in a truck. A four speed auto does not have the luxury of finding a gear that optimizes everything. We either run them to low or too high 50% of the time. As I said previously, gearing down and running higher rpm's is ALWAYS preferable to a lug condition for this application.

 

Here's an article I found on efficient driving.

Also are explained many of the terms we use regarding our Cummins powered trucks.

With all of the new readers in mind, I thought the following might be useful.

Lots of info in Diesel Injection's web site below.

http://www.dieselinjection.net/frames.html


Many people who are new to the world of turbocharged diesel engines hear these terms but may not fully understand what they mean. This article is an effort to explain, in laymen’s terms, what is turbo boost, why you need it, how it affects your E.G.T., why your E.G.T. is important and how you can utilize the E.G.T. readout to prevent heat damage to your diesel engine through the use of a pyrometer.

TURBO BOOST

What is turbo boost? Turbo boost is compressed air, which is produced by the turbocharger and forced through an air cooler and then through the intake manifold to the combustion chamber.

Typically, in a turbocharged diesel engine, the exhaust gasses are funneled through a turbine, which is designated as the exhaust turbine. As the exhaust gasses pass through this exhaust turbine, under the pressure from the pistons, the exhaust gasses rotate the exhaust wheel. A shaft to the input turbine compressor wheel, which is designated as the compressor turbine, connects this wheel. As the shaft turns it compresses the air in the intake manifold and this is termed the turbo boost or intake manifold pressure.

Thus, the exhaust gasses enter the exhaust turbine,

the gasses rotate and drive the exhaust turbine wheel,

the exhaust turbine wheel rotates and drives the input boost turbine,

the input boost turbine compresses the input combustion air,

the compressed input combustion air provides intake manifold pressure and

this pressure is called turbo boost or intake manifold pressure.

Without turbo boost your diesel engine is operating well below its potential maximum power output. It takes a tremendous amount of oxygen to burn diesel fuel. The only way the engine will run without turbo boost is at idle or slightly above idle. Without turbo boost your pickup or coach would move along in first gear with light throttle. Anything over that would result in black smoke out of the exhaust pipe. Thus, turbo boost is necessary to insure efficient performance from your diesel engine.

EXHAUST GAS TEMPERATURE

What is exhaust gas temperature (E.G.T.)? E.G.T. is defined as the temperature of the exhaust gasses coming out of the diesel engine.

Most diesel engines, and perhaps yours, have various parts made of aluminum including the pistons. Aluminum will turn molten at 1350 degrees. Under driving conditions, which put a load on the engine, such as bucking a head wind, going up a grade or driving under high ambient temperatures, the E.G.T. may rise and should be monitored. Every degree of ambient temperature rise is multiplied by three after the incoming air is compressed. It is critical to ensure that engine temperatures are monitored and do not exceed safe limits. The E.G.T. can be monitored as an indication of engine temperature to assure that safe limits are not exceeded. For this reason it is common practice to monitor the E.G.T. in diesel engines in various applications. These applications include large trucks and marine applications. They have not traditionally included motorhomes and pickups. Piston driven aircraft are generally provided with an E.G.T. gauge too. The E.G.T. can be measured and monitored by the installation of a thermocouple in the exhaust manifold just upstream of and before the exhaust turbo. Thus, E.G.T. is a measure of the engine exhaust gas temperatures and should be monitored to ensure that the engine components do not see temperatures in excess of safe operating limits.

PYROMETER

A pyrometer is a gauge that reads out temperature in degrees Fahrenheit. This gauge is normally installed in the dash area, is approximately 2 1/8" in diameter, is attached to a thermocouple installed in the exhaust manifold, and is monitored to provide an indication of engine exhaust temperature. With the knowledge of temperature limits as discussed in the preceding paragraph on E.G.T. the pyrometer provides the capacity to monitor the E.G.T. and to stay within safe operating limits.

Without a pyrometer in a turbocharged diesel engine you are driving blind. You have absolutely no idea of what kind of damage you may be doing to your engine. Forget water temperature as your guideline to determine E.G.T. Water temperature can be at 190 degrees and the E.G.T. can be over 1400 degrees. E.G.T. can rise in four seconds at altitude or if there is a loss of turbo boost.

Every turbocharged engine, whether diesel of gasoline, should have an intake manifold pressure gauge or a turbo boost gauge. This is important because in a general way it lets you know how much power you are using and it also lets you know that the engine is getting the proper mount of oxygen from the turbocharger. As indicated earlier many manufacturers of trucks and assemblers of motorhomes do not provide full instrumentation. Monaco and Prevost motorhomes are provided with boost gauges in the instrument panel.

On a 5.9 "B" or 8.3 "C" Cummins engine there are 14 gaskets, 8 hose clamps, 4 hoses, 1 o ring, and 1 aluminum air to air charge air cooler. If any one of the previous mentioned items were to fail the compressed air being produced by the turbocharger could be vented into the atmosphere and the E.G.T. could skyrocket. Now you know what happens with high E.G.T. A piston failure or melt down could occur and you would be on the side of the road. A pyrometer costs $179.00. A turbo boost gauge costs $38.00. The Original Equipment Manufacturers (OEMs) do not provide them.

This lack of proper and adequate instrumentation has been discussed with many engineers of major engine manufacturers and chassis builders. And I am sure that you know what kind of answers is provided. Diesel Injection has been involved with the upgrading of over 1000 Cummins B and C diesel engines. Owners of diesel engines that are upgraded are truly interested in not only the improved performance but also the knowledge to utilize their improved engines more safely and effectively.

ADEQUATE ENGINE MONITORING AND ANALYSIS

On the "B" engine one pound of turbo boost is roughly equivalent to about 10 horsepower. On the "C" engine one pound of turbo boost is roughly equivalent to about 14 horsepower. So, when you are pulling a mountain and reading the instruments we have recommended (pyrometer and the turbo boost gauge) you can monitor and control your engine and determine the amount of power you are using by watching your gauges.

The turbo boost gauge and the pyrometer are also diagnostic tools for determining power losses. If your turbo boost is low and the pyrometer gauge is running high you have an indication that your turbo boost is being lost. If the turbo boost is low and the pyrometer or E.G.T. is low this may indicate a fuel restriction or loss of fuel.

It takes fuel to make turbo boost and it takes turbo boost to control the E.G.T. If you ever call me with a power problem my first question to you will be "what is your turbo boost pressure and what is your E.G.T when pulling a hill?" If you cannot answer these questions then you will be spending a lot of money on troubleshooting.

CONSERVATIVE AND EFFICIENT DRIVING

One more important aspect of the turbo boost gauge: I’m sure you have noticed how hard it is for your pickup or coach to buck a strong head wind. It is possible to have an E.G.T. in excess of 1300 degrees and be on the level while pushing through a 35 mph. head or side wind. Especially while trying to maintain 60 to 70 mph. Let’s say that your rig requires 11 pounds of turbo boost to maintain your average cruising speed in the level without head wind. With the 35-mph head wind it takes 22 pounds of boost to maintain the same speed. The first thing you should do is slow down, shift out of overdrive and into direct gear. Much more horsepower goes to the rear wheels in direct drive than in overdrive. Less turbo boost is required, the E.G.T. will be lower, the fuel mileage will increase and the wear and tear on the engine will be less.

Head wind or side wind is an engine and fuel mileage killer. Adjust your speed by trying to keep the turbo boost gauge as low as possible along with maintaining a reasonable speed until you are out of the wind. Sometimes it is a long way across Kansas or Nebraska when the wind is blowing. Now, when traveling east and the wind is at your back, oh how sweet it is. You can cruise along using low turbo boost and the E.G.T. is sitting there at 7 to 8 hundred degrees and the fuel mileage will increase by 10 to 15%.

Learning to drive with the turbo boost gauge, the pyrometer, and the knowledge of the E.G.T. will increase your driving pleasure, your fuel mileage and your engine’s life.

FUEL MILEAGE

The first question we would like to address is your fuel mileage. You will not lose fuel mileage by increasing the horsepower and torque in a diesel engine. To insure that fuel mileage will not decrease we install a turbo boost gauge and an exhaust gas temperature gauge with every performance kit. With the performance upgrade provided by diesel Injection your fuel efficiency should improve by 10 to 15 percent. We supply the gauges and provide instruction on how to drive with these gauges.

INCREASED POWER

What are the primary factors in the improvement of performance and the development of horsepower in a diesel engine? Fuel, air (oxygen), timing and compression ratio. The first item is fuel and the rate of delivery of this fuel to the engine is related to the power of the engine. Simply by increasing the fuel delivery from the injection pump, on a diesel engine that is turbocharged, the horsepower and torque will increase. Once the power is increased the exhaust gas temperature will also increase and now more incoming combustion air must be supplied by the turbo. If sufficient incoming combustion air is not supplied the engine would smoke and perform inefficiently.



INJECTORS

Now the last part of the equation is the injectors. It only makes sense when the amount of fuel being delivered to the nozzles is increased the holes that the fuel must travel through have to be increased. The nozzle change on the 1994 and newer "B" series Cummins engines with the inline Bosch injection pump provides a gain of 30 horsepower. Changing the nozzles is a four-hour job and requires the removal of all six-injection lines.

INCREASED BOOST PRESSURE

The provision of additional incoming combustion air is a simple task to perform. This is done by replacing the exhaust turbine housing and providing one with larger exhaust capacity. This larger exhaust capacity reduces engine backpressure and thereby increases the input turbine boost pressure provided by the fresh air side of the turbo. There are only four nuts, two clamps, an oil feed line and an oil drain line to remove before taking the turbo from the engine. Once the turbo is off four more ½ inch bolts must be removed and now the turbo is in two pieces. At this point the technical part of the turbo which is the bearings, seals, and the thrust washers are still intact inside the bearing housing and this does not get taken apart. We do not change the compressor housing or the fresh air side of the turbo. As a result of these changes we have increased the fuel delivery from the injection pump, decreased the exhaust backpressure, and increased the amount of incoming combustion air or oxygen from the turbocharger.

FUEL INJECTION PUMP

Now, lets back up to the fuel injection pump. How do we increase the volume of fuel from this complicated pump? The 1989 through 1993 "B" engines in the Dodge had a VE Bosch pump which requires the turning of two screws to increase fuel delivery. The inline Bosch pump used from 1994 and newer requires a change of the torque plate, which allows the rack to open the barrel and plungers further. There is a helix cut in the plunger. A rack in the injection pump turns the helix to allow more fuel to enter before the cam lobe closes the port and pumps the fuel through the injection line and into the nozzle for delivery to the combustion chamber. The torque plate in the injection pump is the item that determines how much power the engine will develop as long as everything else is correct. This modified torque plate will allow the engine to produce approximately 80 additional horsepower over the stock plate.



ADDITIONAL TORQUE

What about torque? This is the sweet part. A stock 160 HP "B" engine develops 400 foot pounds of torque. With our modifications the torque increases to about 700 foot pounds of torque. It can be expected that fuel mileage will stay the same or improve as much as 15 percent. With this additional power you will not have to run wide open, you won’t spend as much time climbing the mountain and on the level you will be able to cruise effortlessly at 70 mph.

TRANSMISSION AND DIFFERENTIAL SAFETY

Some people ask, "With all that torque, how will the transmission and differential hold up? " As a part of our engine upgrade we provide the knowledge and information necessary to allow the safe and continued operation of the upgraded high performance diesel engines. We have now upgraded over 1000 engines and have never lost a single engine, transmission, or differential.

PROPER DRIVING TECHNIQUE

We instruct you in the proper driving techniques and the proper monitoring of the turbo boost pressure gauge. When moving from a standing start the power required is about 10 pounds of turbo boost or about 35 percent of what the engine will develop. To cruise over hills all that is needed is 15 pounds of turbo boost and 20 pounds for mountains. This Cummins 5.9 engine will produce 28 to 30 pounds of turbo boost pressure and has produced as high as 38 pounds. The Cummins 8.3 will produce 30 to 35 pounds and has produced as high 37 pounds. The turbo boost gauge will let you now when you are going up a grade, bucking a wind or your trailer is dragging hard. This gauge is an absolute necessity for any turbocharged engine, gasoline or diesel.

 

I hope it's ok for me to put this up, since I have before, but this is what Cummins sent me when I asked them about optimal engine RPM range...

 

Great info guys, thanks. That pretty much lays it all out.

On a side note, I was out towing a small load today and I tried pushing the OD button off and on while on the fly, as suggested. When I was going approx 50-55 I would push the button and turn ON the OD. When I did this, the tranny would jump the rpm's from ~2000 to ~2250, hold it there for a second, then drop to ~1400. Does this sound normal and is this what your trucks do???? It just didnt feel right to me. Sorry for all the questions, but I'm just trying to figure out if there is something wrong with my tranny. Shoulda got the 6-speed....

 

Just a little bump to see if anybody can tell me if thier truck acts like mine in reference to my above post.