My uncle was telling me about his new Isuzu F-Series class 6 box truck he has on order. His current Isuzu truck is powered by a 4 cylinder diesel and the new truck will have a 6.7 Cummins. Research revealed that the 6.7 in the Isuzu has 260 HP and 440 lbs of torque. The 6.7 in a Ram truck has 370 HP and 800+ torque. Why the difference? Why wouldn’t Isuzu want all the power they could get out of the engine for their trucks? I’m sure there is a reason. Please enlighten me.
Cummins 6.7 Variations
- Thread starter outoforder
- Start date
Most commercial vehicles are de-rated, for longevity and sometimes registration purposes. The Ram 4500 and 5500 chassis cabs are down quite a bit from the Ram 2500 and 3500s. Eddie the Employee is probably driving those 4500+ trucks full throttle all day long at 30k pounds. Hard on drivetrains!
Companies that buy commercial vehicles buy for longevity and reliability. The 1000+ lb/ft torque and 450+ horsepower in the modern HD trucks is a marketing gimmick. Try running your new GM/Ford/Dodge HD truck at 100% rated power, you'll get it for a minute or two until the computer defuels the engine to save it from extreme heat.
Ag tractors are much the same as commercial vehicles, they are expected to run at 100% for hours on end. The 7.6L tractor I was running last week has 185HP and 600 lb/ft torque. They reject an enormous amount of heat through the cooling system at that power level. Can you imagine running the tractor engine at 1250 lb/ft torque and 500 HP, similar to the power levels of the new HD trucks? You would melt it.
Ag tractors are much the same as commercial vehicles, they are expected to run at 100% for hours on end. The 7.6L tractor I was running last week has 185HP and 600 lb/ft torque. They reject an enormous amount of heat through the cooling system at that power level. Can you imagine running the tractor engine at 1250 lb/ft torque and 500 HP, similar to the power levels of the new HD trucks? You would melt it.
Here is an essay on the topic @wwillson is talking about above. It is geared to the marine market, but it's the same subject. It's from a well respected (marine) diesel power expert, Tony Atherton at Seaboard Marine in CA.
https://www.sbmar.com/featured-article/continuous-duty-a-different-perspective/
The concept you want to get in your head is "continuous duty."
https://www.sbmar.com/featured-article/continuous-duty-a-different-perspective/
The concept you want to get in your head is "continuous duty."
On the lighter trucks, it's just a peeing match as to which 3/4 and 1t truck can have the most torque. No one has any intention of those trucks ever running foot to the floor all day for 500K miles. If they were, that 1000 lb/ft of torque would tear up the transmission, transfer case, differential in short order. It's sad to see, but most 3/4 and 1t trucks really don't work every day. More than likely it'll start dialing back power because the EGTs are starting to approach the melting point of aluminum.
Even if they did, they are relatively light compared to their medium duty brothers and running them foot to the floor, even fully loaded would end up with you significantly over the speed limit and blowing out bearings and tires on a trailer.
In the heavier trucks, they don't have the peeing contest for torque. It's about which one will last the longest with a consistent GVWR of 30000+ pounds all day every day.
Even if they did, they are relatively light compared to their medium duty brothers and running them foot to the floor, even fully loaded would end up with you significantly over the speed limit and blowing out bearings and tires on a trailer.
In the heavier trucks, they don't have the peeing contest for torque. It's about which one will last the longest with a consistent GVWR of 30000+ pounds all day every day.
Great article!
According to the article, for continuous duty, my 6.6L Duramax should put out no more than 230 HP.
They detune them to prevent them from blowing up as much. The ford cab and chassis has less power than the pickup.
Think I'd read that the 250/350 series trucks they pull a lot of power out in the lower gears to keep things together longer. So those maximum ratings are only good in higher gears.
Last edited:
I grew up driving a 1982 GM 6.2L diesel, at 125 HP it was the most gutless truck I have ever driven. The L5P Duramax isn't even on the same planet as the 6.2, simply an astounding difference.I know a lot of it is marketing but man o man I love the power of modern diesels. When I went from my 7.3 f250 to my 6.7 f350 it was eye opening.
I know I use a fraction of the rating but its awesome
I drove it last week, it's still gutless as ever.
Last edited:
Even my 2.7 eb gasser has torque limits. I notice that the top two gears are extremely torque limited. I think 8th is essentially OD and 9th and 10th go beyond. If you lock it to 9th or 10th manually, you only get the first 20% of pedal travel or so. want the throttle to open more, gotta choose a lower gear first.
in one of my Volvos, if you slapped the throttle down from a stop, it would immediately shift to 2nd and skip 1st.
i can see programming like the above making sense.
Similar threads
