Has anyone ever noticed that whenever the same diesel engine is used in a medium duty truck as well as a pickup truck, the PU engine ALWAYS has lots more power and torque?

For example, the 6.4L PSD is rated at 350 HP and 650 lb-ft of torque...but the same engine, which is known as a MaxxForce 7, is used in an international medium duty truck, it's only rated for 230 HP and 610 lb-ft torque...with only one borg-warner turbo?

Why is the 6.4L is the F-450 in some configurations tuned down to 325 HP and 600 lb-ft? Wouldn't you want MORE power in a heavier truck?

Why?

 

Soon to be corrected if I am wrong, but, I think that medium duty trucks have transmission gearing that is engineered better for hauling the weight that they are rated for. Our pickups are handicapped with a transmission that is engineered for daily drivability so people don't complain about it being too much like a truck.

They also have worked hard on diesel motors to make them drive more like gas motors 'cause of all the complaints from the average drivers. None of us here are in that category, we all wish our trucks were more like trucks.

 

Good point.

However, I can't imagine a time when more power would be a bad thing when you're trying to muscle around that much weight day after day.

Drivetrains are definitely different in the heavy truck market, but I don't think they are vastly different in medium duty trucks. Sure, the components are rated for more weight, but I believe it's common to see 6-speed manual trannies as well as similar automatics in medium duty trucks.

Heavy trucks use a driveline setup optimized to keep the engine within a very narrow RPM band, as the larger engines operate best in that small range. For example, my work truck is a 2006 Kenworth T600 with a 450 HP caterpillar C15 engine, and a 13-speed transmission. I like to keep it between 1200-1400 RPMs all the time, which is why all the gears.

But many medium duty trucks use the same engines we have in our pickups...the cummins ISB is one of the most common ones available. Since when does a pickup need more than a medium duty? And also, why is the engine rated for a certain rating in a pickup, and that option not even being available for larger trucks?

And I just looked at the Navistar MaxxForce website. For the 2010 emissions, the MaxxForce7(AKA 6.4L PSD) does use dual turbos, and is rated up to 300 HP and 360 lb-ft of torque. Strange how they strap two turbos on and give it more power for the 2010 emissions, but not the 2007 emissions.....

Thanks for the quick reply...I'm very interested in seeing people's thoughts on this...

 

one word --- MARKETING to a different group

Sales to the mass market is about marketing.... to the 'dump truck' market is about power.

 

One limiting factor for a truck, as the GVWR gets heavier, is engine power, how much do you want to spend for a transmission capable of handling X amount of torque for a 35,000 GVW rating? How much power do you need? Would you be willing to buy the $3,000 optional transmission to go from a 560 ft. lb. torque engine to a 660 ft lb. engine?


International is doing the 2010 emission standards without urea and is going to dual stage turbos as part of their "Advanced EGR System" on most of their engines to facilitate the effort. They report a price increase of $6,000 per truck/bus for the new standards.

 

I figured it was a longevity issue...

Basically, less power = less stress on internal engine parts.

Which is true to a point, but some things make me wonder.

For example, our flatbed we have at my work is a '96 Ford F-800. About 24K GVW, the truck itself weighs right around 12,000 lbs.

It's powered by a 160 hp-400 lb-ft 12-valve Cummins, with a 4 speed Allison behind it. It's not TOO bad most of the time, unless you have to go up a hill, then it generally sucks. Main problem is that the Allison feels like a 3 speed overdrive...First and Second gear will actually get you up and going pretty quick, third isn't too bad, and once it drops into fourth it really bogs down, especially uphill (loaded it's even worse, you usually don't get into fourth on a hill when loaded). Most of the time you have to run the **** out of it to travel at a decent speed.

On the plus side, it does get 10-12 mpg even when loaded.

 

That's exactly it. The heavier truck will be using all that 160hp almost all the time. An engine at max power and max governed rpm is where they have to live. The pickups arent loaded often(as a whole), or most customers run unloaded. You can really crank up the power with only 6500 pounds to drag around. If they did a 350 or 400hp Powerstroke in a Med duty, it would be fun, but would run too hot, and wear out way too soon.
Less power also means vengeful drivers are less likely to break the rest of the drive train.

 

they do power test in the development stages of all these motors. they beef them up and get the most power out of them possible and then let them run at that power until they die. usually 24 hours. then they have a formula that if they cut down the HP this much the engine should last this much longer. and so forth. My dad used to be a diesel mechanic for a heavy equipment place, and he told me that the motors that were in the bobcats were capable of making 5 to 600 HP but they only put out 50 to 70 HP in the actual unit. Its because if you build a motor to run for 24 hours at 600 HP then how long do you think it will last only running at 50.

 

Ya'll are all overlooking something:

Horsepower is a calculated measurement, that actually has very little to do with how much work the engine can do in the real world.

It's a calculated measurement based on engine speed.

Larger engines turn more slowly, so their HP figures will ALWAYS be lower.

An example: My Detroit Series 60 is rated at 1650 ft-lbs of torque. At 1200 RPM. 485 HP at 2100 RPM.

A PSD is barely off idle at 1200 RPM, and is certainly nowhere near full boost. At 2100 RPM, the PSD is barely halfway through it's rev range, whereas the Detroit is just short of redlined.

Remember: Horsepower sells engines. Torque wins races.

-blaine

Which would you rather have pulling 45K lbs?

 

It's simply for durability because heavier work trucks are designed to haul heavier loads and go many more miles than pickups.

This is why the International trucks have far fewer problems with EGR coolers, headgaskets, etc. than the Ford trucks with the same motor.

 

More HP/Torque = twisted drivelines and broken axles. A pickup will usually have thousands of pounds less weight to get moving. The drivelines and axles are not under the same stress big trucks have. I know big trucks have bigger/stronger axles, but the engineering nerds have determined that the manufacturer will have less problems at a certain HP level, so that is where they build the engines to. You can get waaayyy more power from the Powerstroke/Cummins/Duramax than comes in stock form. When you do the transmission/clutch/drivelines suffer.

 

look at tractors for example. 125hp is plenty for a tractor and they can go up to 10,000 hrs if they are properly maintenance. Are 4240 is well over 10,000 hrs and as far as I know we havent done any major work on it besides a new Hydraulic pump. Plus with lower HP ratings people arent going to get to crazy roding it around.

 

That sounds like a 450 dually with 4.88 gears. They detune it with the gears that low so "you dont brake anything". A friend of mine works for ford and was telling me about this

 

They do it to bump up reliability.

 

When your talking about any of the engines used in P/U trucks and same engine that is used in medium duty trucks the one in the medium duty is derated so it won't have a melt down.

The 5.9 Cummins is a gutless pig in a medium duty truck you have to keep them rated low or they just fail. A small engine isn't designed for a real truck.

Same with the 7.3-6.0 and 6.4 used in medium duty trucks they are maxed out with a F-550 with a 19,000lb gvw.

All the Cummins lovers better drive a medium duty truck with a 5.9 Cummins and see how poorly it does. They might change their tune calling the 5.9 a medium duty engine. The truck is grossly underpowered.

International has pretty much the better medium duty engine and it is the 466 it works good in trucks from 20,000lbs to 30,000lbs it they are a little underpowered in a 35,000lb gvw truck.

The 8.3 Cummins isn't too bad, it is far far better than the 5.9 that shouldn't even be in a truck with a gvw greater than 19,000lbs.