The only advice I got was on this forum. I don't trust the equipment dealers to tell me all the facts.

Diesels operate on torque and if the engine and tranny are matched you should floor the accelerator until you reach the cruising speed. They do not operate like gas engines and your performance off the line is a function of torque, which peaks at the lower rpm range and tails off as you reach maximum rpm. Your turbo pressure will also be greatest with full throttle and at lower rpm's. My CAT 300T only produces 8-10 psi boost and that occurs off the line and on hills. I find acceleration fine as it operates just like the city bus it is based on.

Tom,

We are probably going to violently agree for the most part, but Torque and Horsepower are different expressions for the same thing. Torque being the force of the turning crankshaft, but HP being a value of that same thing over time (one horsepower is equal to 33,000 foot-pounds of work per minute).

You are right about the way we need to drive a diesel, but it would be no different if it were a gas motor that produced the same torque over a low RPM range. In the case of diesels, the long stroke of the piston limits the RPM. This does make the transmission critical in getting the torque into a useful form you might say.

The turbo question is interesting. Obviously the turbo vanes spin off the gas exiting the motor which are connected to another set of vanes that create intake boost. Traditionally, turbos have "lag" at low RPMs as they are not spinning fast enough to create optimal boost. Then when the engine is spinning really fast, they struggle to create boost as the air is rushing through the engine so fast as to require too much volume to get boost. Hence, there is usually a sweet spot where everything is perfect. It makes sense that low RPM diesels can maintain this sweet spot better than a high reving short stroke motors as they don't have nearly the range to deal with. Again, the transmission is working extra hard to apply the engine's torque in a usable manner.

So we do agree, mash that pedal to the floor and aim between the lines!

Any internal-combustion engine should have the throttle feathered on both acceleration and deceleration, thus moderating heat buildup and recession. While engine blocks are quite robust, it's advisable to avoid testing the limits, long-term.

quote:

Originally posted by Rusty:
Any internal-combustion engine should have the throttle feathered on both acceleration and deceleration, thus moderating heat buildup and recession. While engine blocks are quite robust, it's advisable to avoid testing the limits, long-term.

But that would make my lap times drop off!

quote:

Any internal-combustion engine should have the throttle feathered on both acceleration and deceleration, thus moderating heat buildup and recession. While engine blocks are quite robust, it's advisable to avoid testing the limits, long-term.

I can see where a gas engine can benefit as you would be dumping excessive fuel in, but aren't you just dumping air in a diesel. Seems like it would add no stress and simply spool up at its own pace.

In any case, there is a reason that the throttle is variable! I've driven with people who might as well have an on/off switch for throttle and brakes and it is both degrading to the equipment and the nerves.

My record for full throttle has to be in my old MCI. Middle of the night coming up 81 to 84. Could have put a brick on it from Maryland to Newburgh, NY. No cruise meant my right foot would get tired from just sitting on the floor. Gravity was the speed modulation on that old DD6V71.

I normally comment on Diesel Engine topics. As you've noticed I've stayed out of this one as I don't work on the 5.9 Engines so I really don't know too much about them.

Speaking in general terms... There are fuel plates you can install in the pump. There are fuel pump adjustments you can make. You can increase the exhaust and intake sizes. A bigger turbo also helps with power improvements. You can install non-emissions injectors that are used in boats to also boost up your TORQUE.

The notion that HP is the same as torque doesn't really translate very well when talking diesel and gas.

Corey Noble is right, for the most part, in his description of what happens. You do need to "Mash That Pedal" to the floor to get a diesel to spool up the engine properly.

Limiting factors on acceleration, in addition to what is listed above, also includes how large the fuel suction line is, how long the fuel has to travel from the tank to the engine and how many fittings or restrictions are in the supply line.

A general rule is that each 90 degree fitting is about the same as adding another 7' section of fuel line. Too small of a line will limit the fuel that is available to the pump thus restricting how much fuel is available when needed.

You also need to keep in mind that when someone installed the fuel tank it might be restricted in the pickup tube. Plenty of time when "bumping up an engine" you'll also need to increase the fuel line opening in the tank. In a perfect world this would be accomplished by replacing the pickup tube in the tank. Some (not recommended) use the biggest port on the bottom of the tank to accomplish this.

Increasing the volume of the filter element is also another spot you might need to look at when more volume of fuel is required during acceleration.

Another thing to ponder is hearing people say, ever since I increased the power of my engine I now get better mileage. It seems a contradiction that using more fuel will give you better mileage. It isn't a contradiction... it's simply more efficient to overcome the transmission, rear end, tires during acceleration with a higher Torqued/HP engine. You've also changed the "Sweet Spot" of the engine thus making it more efficient within the range that you normally run.

When someone says "I need more power" you also need to understand their uses and their expectation as well as the limits of the vehicle... Unless you're racing these things, you simply are not going to get a diesel to move down the road like you would a car.

In a fleet like Penske or Ryder I have to constantly chase someones expectations against the reality of the application.

A 5.9l engine will only produce a certain amount of safe torque and HP. Anything above that will wear out engine parts faster.

Unless you understand Exhaust Gas Temperatures or EGT's you will basically turn your pistons into a molten mess... Here, if you know what you're doing, you might be tempted to install a charge air cooler too.

This is not the end all of what needs to be considered. Rear end size, tire size, tire material, how many miles are on the engine and the transmission ratings also needs to be considered.

This is why I hardly ever make a statement on how to get more power out of your diesel engines. I don't want to help you lunch your engine if it isn't capable of what you want it to realistically do. And, realistically speaking... The 5.9L in a Barth needs a lot of modifications to do it right.

It's always good to have you chime in as your experience is unsurpassed in this forum.

One thing that translates across gas, diesel, propane, nuclear........There's no replacement for displacement! IMHO

As you all know, I have the 5.9L Cummins and have done a ton of research how to improve the performance without degrading the overall lifetime of the engine. I had a fleet of trucks (years ago) that were diesel powered and was directly involved in the operation and maintenance of those.

There is a lot of facts and a lot of fiction out there, unfortunately, not easy to tell which is which! 5.9L Cummins as found in Dodge trucks can be modified to produced 1000s of HP and more then 1500 lbs/ft torque, BUT at a dear cost of engine life time.

My comments:

1. I absolutely agree that there is no replacement for displacement, doesn't matter, gas, diesel or any other form of internal combustion engine!

There are upper limits on the HP and/or torque demands that will greatly effect the lifetime of the engine. I said it before, the life of an engine is inversely proportional to the amount of fuel that is forced thru it!

2. Larger turbo will generally provide the ability to get more power out of an engine but at the cost of spool-up time. In addition to the turbo, the fuel input will have to be increased, now there is a limit to how large one can go because of the upper end EGT limits. Boost is generated by the salvaging the heat from the exhaust, more fuel, hotter the exhaust, again to a limit. My engine will not hit full boost of 20 lbs until I cross 1900 RPM.

3. One thing for sure, diesels should NEVER be lugged, particularly rear engined coaches that depend on an engine driven fan for cooling! When going up a grade, as soon as you reach the upper end of the lower gear, you should shift into it. My upper RPM limit (often referred to "top of the governor") on the 5.9L is 2800 RPM, I keep a chart that shows the speed in each gear at TOG, and as soon as my speed slows to within the range of the next lower gear, I manually shift into it. My EGT drops, the cooling is better, and I can maintain a greater speed up the grade. Even then being able to keep a certain Rpm up the grade, I sometimes have to back off because of EGT limits or water temperature limits.

4. Lastly, one thing that has not been discussed much in these past threads is gearing and tire size!!! Gearing IMHO is just as important as torque or HP.
ie. I have an Allison 6 speed, 4.1:1 rear gears AND 8R19.5 tires (original size, have 225R70 19.5 now), the trans shifts into 6th at 58 MPH, how ever Richard's Breakaway has the same engine and trans but has 22.5 tires and he shifts into 6th at 65 MPH. That also means that in the lower gears he will have a faster speed at TOG, but will not have as good acceleration off the line as I do.

There is a trade off between acceleration and cruise speed. Owners of earlier 30' Breakaways have 3.73:1 rear gears, and a 4 speed transmission. In 4th gear the maximum speed (at TOG)would be ~73 MPH. Better prospective would be at cruise of 65 MPH = 2489 RPM, where as mine will cruise 65 at 1778 RPM.

For acceleration considerations, the 4 speed transmissions and the 6 speed transmissions have nearly the same ratio 1st gear. (4 speed = 3.45:1) (6 speed 3.49:1) mated with the rear gears the final ratios for 1st gear are: 3.45 X 3.73 = 12,86:1 vs. 3.49 X 4.1 = 14.31:1 The 6 speed has nearly 12% better torque multiplication with the same engine in 1st gear.

My quest for more power will be limited to increasing the size of the engine, if I keep the Breakaway long enough, it will have a 8.3L 300 HP engine. I do not intend to try to increase the HP of the existing 5.9L engine. The 8.3L is about 4 inches longer and will present some installation challenges but is very doable!

quote:

........There's no replacement for displacement! IMHO

..and cubic dollars far surpass cubic inches or cc's

quote:

Dodge trucks can be modified to produced 1000s of HP and more then 1500 lbs/ft torque, BUT at a dear cost of engine life time.

Just like a light bulb, you can increase the volts and get more light at the expense of lifespan. If you need more light, sometimes it's better to get a higher wattage bulb.

quote:

Originally posted by MWrench:
...the life of an engine is inversely proportional to the amount of fuel that is forced thru it!

I hope it's not lost on anyone that the higher the torque/HP the beefier the driveline needs to be. You'll snap axle shafts, snap U-Joints, break yokes, twist driveshafts and blow rear ends.

What is safe has everything to do with how you drive it.

You have a choice... The engine can be the governing factor, or you can be the governor, or the twisted driveshaft will be the governor.

Based on what I've seen out there... there are VERY FEW people who will drive a modified setup just below the weakest link.

quote:

Originally posted by Bill N.Y.:
I hope it's not lost on anyone that the higher the torque/HP the beefier the driveline needs to be. You'll snap axle shafts, snap U-Joints, break yokes, twist driveshafts and blow rear ends.

I agree with that statement for sure. Must have been a good reason why Spartan went with the Eaton axle instead of the Dana axle with the 230 5.9L and 6 speed. I have seen the Eaton diff behind 400 HP units and the 6 speed is very well known to handle much higher HP. The early units like mine are somewhat suspect, and one of the big changes made is throttle feedback from the trans to the engine on the electronically controlled "common rails" engines to reduce the throttle during shifts to relieve the transition shock. Most cars have used this for years and only because the manufacturers can downsize the transmission.

quote:

Originally posted by Bill N.Y.:
I hope it's not lost on anyone that the higher the torque/HP the beefier the driveline needs to be. You'll snap axle shafts, snap U-Joints, break yokes, twist driveshafts and blow rear ends.

quote:

Originally posted by MWrench:
I agree with that statement for sure.

Then, based on someone having a 140-190hp 5.9l engine, would you think that giving them the information required to overstress the driveline is really a good thing?

My issue with this is that little is being directed towards the eventual self destruction of major dollar components.

My thoughts also have to do with looking at other things too.

You, me, Gary and a few others can handle this. But, I know that even I could have problems under the right circumstance if all I did was bump the motor up.

I know we agree on this. I'm just explaining why I haven't said anything and have been ducking responding to this. I'm not as clueless as I originally stated when it comes to turning one of these up... I just don't think that all of this works out as a positive unless more things are considered.

I think we can agree that someone who has one of these need to be well prepared to have a melted down 5.9l. I think we also need to educate everyone on the major damage that can result from doing this.

Too narrow of an exhaust and/or intake size could result in more damage too from washing the cylinder walls down with diesel fuel. They also make different pistons for the higher HP engines. At the very least, turning one of these up to produce more power needs to be coupled with a stern warning and imploring them that reading EGTs, watching cooling temps and keeping the engine revved up is a mandatory thing.

Turning up, then driving a loaded 5.9l Barth might exceed the rated capacity of their coach just from the simple act of a tire spinning and then grabbing on grass/pavement.

Stupidity, in this instance, can be closely related to ignorance if nothing else is considered.

We might live in the age of the Information Super Highway. But, you'll be sitting in the breakdown lane going nowhere quick if you just turn up one of these and then stick your head in the sand.

Following Bill I wonder why anyone with an 8 ton motorhome cares about acceleration - the "bigger than you are" rule says people will change lanes or slow down and when the money and effort is invested to gain maybe a second or two why bother. In my CAT 300 Turbo the factory build sheets show the block, pistons and manifolds are very different -- there are additional coolant passages to deal with the heat and the pistons are thicker and have different wrist pins and the crank has a different journal size. I can't keep up with the Greyhound Bus or the Prevost rolling along at 80 mph, but when I think of how much he lost when he drove off the lot, I smile and pat the aluminum dash.