Josh, as an engineer, I have to commend you on your thorough knowledge of the engineering principles of engine design.

I'm a colleague of you from Iran, and man do I enjoy it when I see that someone speaks with knowledge. All you said was correct, and you earnt yourself a new subscriber. Basically: Best fuel economy: torque span Best accelration: max torque to max HP Very low RPM with heavy load: destruction of engine

"They tried to clean it with a shovel, or a stick of dynamite" lol

I never see a mechanic get this correct. when roilling down the road with low engine load, sure take the rpm down lower, but any time you are pulling hard let it eat with a bunch of rpm. your fuel economy will be far better then a dummy lugging up a hill at 1200rpm with a ton of egt. the pyro will tell you how to drive the truck better then a tachometer

For my 2004 Cat C7, in my 40' motorhome, I allow the Allison Automatic transmission to pick the best RPM and Gear, UNTIL, starting to climb a grade...then I watch the coolant temp very carefully and if the engine starts to drop below 1500 rpm, and the temp starts to climb, I manually select a lower gear which allows the rpm to go up to about 2000 to 2100 rpm, and let the speed drop. Usually the "sweet spot" is 3rd gear, 2000 rpm, and the speed will be about 35 rpm. This is what works for my motorhome, but the best rule of thumb is reduce the gear, until the vehicle can accelerate up the grade, then reduce the throttle until you get down to the sweet spot. At the "sweet spot" the engine is generating enough torque to climb, and most importantly the fan is spinning fast enough to push enough air through the radiator to keep the engine cool. Everyone wins! Josh, thanks for another great diesel video. BTW I love the special effects.

You just explained why Gale Banks of Banks Power wants to turn a 2,000 RPM Diesel to turn up to 7-8,000 RPM... Thank You.

On a couple Harley forums I have joined, it comes up every once in a while, "what RPM is lugging?" Too many variables as you say. Uphill? Downhill? Part throttle? Full throttle? Road speed? Parking lot speed? Cruising speed? Headwind or crosswind? Tailwind? To me, at cruising, an engine speed at which increase in throttle position produces an appreciable unlabored increase in engine speed and road speed is not lugging. Best explanation of torque vs horsepower I have seen on KZfaq to date by the way.

University level explanation of a topic. Clear and understandable even for the masses. Another great diesel video.

As a locomotive mechanic, I love explaining this to people. One of hour engines makes 4500 hp at 950 rpm. Compare this to a top fuel dragster which makes 11,000 hp at 9500 rpm. We make almost 25,000 lb-ft of torque while a dragster only makes 6000. This means two things. Firstly, due to the rpm involved and the fact that they have 500 cubic inches compared to the 11,000 cubic inches of our engine means that their engine may have almost triple our power but wouldn't have even a quarter of our pulling power. Secondly, our engines are designed for a sustained output load. We can make 4500 hp for hours and hours. Technically barring mechanical failure and refuelling we could hold that power level nonstop. A top fuel dragster can hold that power output for a matter of seconds, and with the frequency in which they blow up on the track it's clear that's pushing the limit

I have found that my Pyro temp stays lower when I work my 6NZ at a higher RPM. More air though the engine. Also, I have talked with transmission rebuilders and they say they are noticing more wear with the "gear fast, run slow" spec trucks. All that torque wears stuff out in the trans and diffs.

DESTRUCTION OF THE WEEK IS BACK!! Ahhhhhhh yeah

EXCELLENT video Josh. I get asked the same question by boat owners all the time, outboards, cruisers with small or big blocks, some with yachts & 3208s, 3406s, etc. I have always deferred to looking up rated tq/hp specs at respective RPMs & tell them to split the difference. Those who have followed my advice seem to never have problems & report favorable fuel consumption numbers. Looks like my theory wasn't far off... Next 1 that asks, I'm gonna start this video & hand them the phone.

You have answered questions I’ve had for a long time. Thanks for the great content!

My uncle taught me to always match your rpm’s with your road speed. His equipment always looked like it came off the showroom floor. While most of the guys would be driving the piss out of their trucks during the day, he would be right there with them using less fuel, less wear and fatigue on his truck.

The owners manual of a a car I had years ago said "Drive in the highest gear that gives you the acceleration you want". Using the engine you showed data for, lets say that you were on a road that was perfectly level, and for legal reasons you had to go at exactly 50 MPH, and in those conditions the vehicle requires exactly 200 HP to counteract the air drag, it would be okay to be in a gear that caused the engine to spin at 1,050 rpm as the engine would only be producing 1000 LB-FT of torque, or 57% of what the engine is rated for, if the road started to have a slight uphill grade, the HP required would go up you would need to give it more "gas" to maintain the same speed until the pedal is about 7/8 down (as a general rule of thumb, when below running the 'max torque RPM' [in this case 1200], depress the pedal no more than the ratio of the RPM you are at to the Max torque RPM, [1050÷1200=.875=7/8]) , at which point you would downshift to bring the RPM up.

Thank you for that explanation, it's the first time I've heard a good explanation of the relationship between torque an horsepower. Keep the good stuff coming.

Dude you have one of the smoothest voiceovers ever!

that was the best and easiest to understand explanation of torque and horsepower ive seen, and ive seen and read a lot, and ive been around a while. great work.

Always enjoy your videos, I own my first diesel and have always loved diesels for some reason.

I drive myself crazy trying to explain torque and horsepower to people. You did a nice job. I run my cars and trucks at what I feel is the harmonic balance. Never had a car or truck that didn't have a speed where everything was harmonically "happy" at "x" speed. People think I am weird, but my stuff don't break.

I used to drive a Kenworth K100E with a 3406B that had a nice little increase in fuel pressure prior to me getting it. On an extended climb that thing would pull down to 1000rpm an have egt at 560 which was well in the yellow but regardless of how much steeper that climb got, that beautiful cat engine wouldn't lose a single rpm more. The exhaust stream out the top was like a jet exhaust pipe roaring due to gas velocity and always had a nice black haze to it where it was running slightly rich of peak. Needed that heat tho when she was cold wouldn't quite pull a planet like when it was on the boil at that 98 deg C water temp. Would recover from that 1000rpm with a vengeance at the top too. Aint nothing like a caterpillar engine!

Love these topics. Nice length video and really enjoy your deep explanations.

Running a working tractor ploughing it was up to the temperature. Free spinning and the correct gear selection is important.

Depends on many things, but Cats like 1400-1600 rpm most of the time ( big block Cats.....15L and up ). The Series 60 Detroit I drive likes to be between 1550-1650 rpms in the flatland and 1800-1900 pulling a grade. Gets best mpg between 1450-1650 in 1:1 direct

You never bore me you are a wealth of information, I watch every on of your videos to the end. How about a 3306 fuel injection pump episode, specifically the one that came in the mep007b military generator

I really appreciate your sharing your knowledge of diesels and explaining it so even I understand! 👍🇺🇸👍

It also depends a lot on the compression ratio, in the Cat c18 with 14:1 compression ratio the sweet spot where there's the lowest fuel consumption is between 1400 and 1600 RPM, similar with the C15 and 3406 with 16:1 compression. For the Road use ones which are the C18s with 16.5 :1 and C15 with 18.5:1 compression is between 1200 and 1400RPM, with higher compression the torque curve moves down, but there's also higher pressure and temperature, at 1800 RPM which is normal in marine engines the cylinder head would overheat and crack, while the low compression C15 can go rather well in the 2000RPM before head overheating problems

Olá , sou aqui do Brasil , eu vejo teus vídeos sempre ,, eles são ótimos ,vc explica bem , tank you.

wish I could give you billion views on this on here.... Also wish I could sit in a class taught by you

Wow incredibly informative. I understood how intercoolers and turbos affected an engines power but I didn't understand some of these seamingly simple points.

Excellent vid on the pros and cons of each scenario love that channel

Hey Awesome video. I love watching your videos I’m always learning something. You make awesome videos. You should do a tool box tour next. Love to see the set up you have being the kind of mechanic you are.

Very information and explained well. Let's not forget the boom lol nice touch.

I knew all of that stuff, but your explanation is one of the best over the internet! There is trucker on YT, doing heavy stuff and runnin it's 15L Cummins uphills at 13-1100 rpm....he doesn't know that he should do 14-1600. It will be better for the engine and even for fuel (cause slower speeds (i mean really slow) means lover gear and higher rolling resistanse)

I truly enjoy your videos. Your able to put this information to simple 1 + 1 = 2.

Great video today Josh!

Yes, new vid. I’m learning all about Cats, since I’m about to buy a 94 Pete 379 with a 425 horse Cat

Thanks for the explanation 👍

Great short answer!

Very well explained. Thank you

Nice vid Josh

I was just wondering this very thing today, as the auto transmission on my Cummins was running around 2500

Very informative video like always, Josh🙂The only thing I'm thinking is when you said that running at higher rpm won't make a significant difference in fuel mileage, but running at lower speed will give a better mpg.Yes,and lower speed means lower rpm 😁

1800 RPM on trucks ,farm tractors and bull dozers is the sweet spot on our equipment .

Along with piston speed based on stroke, you would have to consider piston acceleration, dwell at TDC and BDC. Short stroke motors have shorter duration dwell and high acceleration rates that generate high G loads that don't favor high mass components.

I miss my 3406B. It was low power,,,,,310 but man it would pull hard at 1150 and keep going. I had a pilled up 3406b in another truck, but would fall off the turbo lower then 1300.

Well done! Engineering Explained did a similar video going in depth on HP vs TQ and acceleration using similar and derivative equations

Thanks for Great Informative and Educational Video. Time to Learn new Information : )

My 3406E 1LW is currently at 475HP 1750Lbs torque I like to run it between 1200rpm and 1500rpm when shifting gears at flat roads and when I hit the hill I keep it at 1700rpm max depending on the load I'm carrying I try as you said just the necessary rpms no more no less and I never push the right pedal to the floor,never... I've been having this truck for 7 years by now and it has more than a 1 million miles on it,I don't know if it was rebuilt before it came to my country (Costa Rica) but it is the best truck I've ever had... I always thought that if you drive your truck at the lower rpms needed you'll get more durability because it isn't turning everything up and wasting torque and if lower rpm speed then longer the engine will last... As always very good video pretty informative and interesting facts... Keep them coming...

excellent video!!! Very helpful

great explanation

If it's a Detroit. On the floorboard. But cat on a long pull I'd say at peak hp, but other conditions...peak torque

In my truck peak torque comes at 1800 rpm and peak hp at 3500rpm....I just cruise at 2000 rpm....no stress for it and plenty of power

Great video

when you tighten a bolt, (torque x angle through which you turn) is energy. you put energy in, where'd it go? A little to heat, but most of it is stored in the tension that you leave on the bolt. youre stretching it like a spring. (now here's the good part:) energy is in joules. power is in joules per second, ie watts. plot how many joules you've put into that bolt, over the time you turned it- that'll be a line that goes up with each second, cuz you keep on turning and keep on adding stored energy to the bolt. then the slope of that curve is how much power you were applying (how many joules per second) at every instant. HP is also power. 1 hp is exactly the same as 746 Watts.

Thank you.

Thought the answer was always another question. Who owns the machine? Company machine? On the mat as often as possible, it has a rev limiter.

Understood, thank you

A high torque load at low rpm is hard on everything from rod and main bearings to transmission and rearends.

Just wanna say thank you for sharing your knowledge and and in doing so helping people. I made a little donation for you at PayPal. God bless you.

Some damn sweet dpf's man Wholly hell

good video on torque and horsepower.

HP is the work and TQ is the force.

great video👍🏾 i run cattle and we tend to run our B model up around 1750 1800 ish loaded and then unloaded i like to run 14-1500ish but seems to me the ole B likes to run up a little high i've seen her take 1850-1900 pulling heavy and have PLENTY of power on top end

I wish I knew half the stuff he knows about engines I've learned alot just watching his videos

I've always understood that the besh fuel economy came from running the engine at the speed of its lowest break specific fuel consumption point which is, as I understand it, the same speed as the peak torque.

Also wondering about wear vs rpm. Or piston speed. More of constant rpm situation.

Yep, I would run a c15 between 1500 and 1800. On flat ground 1600 and in the hills I would be 1800 hitting an ascent. At the crest of the hill experienced guys will back off on the fuel to get more torque and prevent whipeing your feet, mine is a simplified explanation. I am not a mechanic but have driven for a few decades in heavy haul.

Max torque on my '02 Dodge/Cummins HO is at 1600rpm. For what it's worth the engine seems to just purr at around 1750rpm or so. Also, if you hit a hill etc and rpm wants to drop...it drops right back into peak torque and easily pulls itself back to 1750. I will force a downshift if I see a steep hill coming up (moderate load with full time camper and gear) but generally the engine seems to hold it's own in CC with little effort. Fuel mileage alone might tell you your best rpm.

Hello Mr. Ape. I’m digging the channel as I think it’s extremely informative. Especially for a guy like myself who knows very little about Diesel engines and how they work. With that said do you or have you done any videos of say non-commercial use Diesels , or do I dare say Ram 6.7 diesels in particular? Reasons I ask is because I noticed you had videos of a used Chevy truck, an electric bike, normal bicycle & because you guessed it I own a Ram 3500 DRW Diesel. Anyways there are very few channels out there that explain things and go into depth the way you do all while speaking in a way so a Knuckle dragging Neanderthal like myself can understand. Thanks for the videos! ✌🏽

10:59 picasso animates the combustion cycle

I overheard a driver say to a mechanic one time that he was disappointed in his engine’s torque and horsepower when climbing hills. The mechanic asked if the driver took a “run” at climbing the hills. The driver said not really. The mechanic answered, “your not running out of torque and horsepower, your running out of speed!”

Well done sir!! I'm trying to find this exact same video for gasoline engines but I cannot. I just got my engine rebuilt it's a 97 5.7 litre vortec and it's a 5-speed manual so I can select what RPM I choose to drive it around in. And I can't seem to find the specs from GM.

The first example of torquing a bolt ignores that work was done TO produce the torque. Energy was put INTO the lever and then the bolt. HP is (according to some engineers/physicists I’ve heard) a mathematical function OF torque. Good vid, nice destruction (glad they are back). I’d love to see a discussion of what each (HP and torque) does, as it applies to driving a heavy truck. When is higher HP desirable? Under which conditions? When is higher torque more desirable/why? Which is needed to accelerate, which to maintain speed on a grade? That sort of talk.

Hi BR, First of all Thank u for all informative videos. Quick question plz, I have 2012 freightliner cascadia dd15, I do see blue smoke coming from exhaust, it doesn't happens everyday just once a week or in 2 weeks. I noticed that mostly when I'm loaded. I have no check engine and oil level never drop from oil change to oil change. No leaks and no turbo leaks. I been trying a lot of shops but no one could get to the point specially when I'm at the shop and truck has no smoke at all, they couldn't figured out. 1 guys told me maybe is bad fuel. What do u think Josh?

You turn your radio off and listen to your motor. It will talk to you. When you go into a hill as it starts pulling you dont stuff your foot in it. You slowly back out of it and listen when you find the sweet spot you will hear it and it will pull a hole in the wind. Try it it works.

for class 8 trucks it's all about the torque.

Power is Force (Torque) versus Displacement (RPM). Without displacement, may have static torque but no power is consumed or produced.

What power is good explains torque on wheels chart for every gear. It shows that torque on wheels on 3rd gear is bigger on max power RPM than o 4th on max torque RPM at the same vehicle speed.

If you have time I could really use your help thank you

Josh: I own a couple of Mercedes 240Ds, and work on the engines by myself, with a certain degree of success. However, after refurbishing the fuel injectors (new nozzles and all) a few years back, now I got reason to believe they’re now popping at a lower pressure, reducing horsepower as time goes by. There are no leaks and workmanship is fine, and I fear the issues are either the chims or spring metal fatigue. What are your thoughts on that? I’m looking at replacing them, again, after only 35,000 miles. Valves checked fine. Fuel filters are new. But power is really down an efficiency dropped from 31 mpg to 20. Any suggestions? G

Cummins recommends 1450 RPM for efficiency where the truckn will spend most of its time: 65 or 70 MPH; 1500 for performance on the N14 ans ISX15. Personally, my 2000 Cummins N14 engine likes to spin to breathe as evidenced by the instant fuel meter. It will do 1,300 bobtail or empty w/o head wind but 1,500 is much better sounding and better instant fuel mileage when haing heavy. 1,500-1,600 uses the turbo less than 1,300. Lugs and bog when heavy at low RPM, but chops them hills down with the edge of its hand at moderately high RPM. Mounteagle I slay at 1,800 RPM. EATON 13-Speed allows the fine tuning in cities or other slower roads. It is a deal- breaker for me to own a truck-tractor that comes with less than 13 speeds or an automatic. Exceptions.: 22' dumps/short city day cabs wiring in the city or vocational.

Thanks A A. How about the c7 that turns at 2475 rpm. Thanks.

I’ve driven CDL trucks for over 25 years . I also have known a few professional diesel mechanics. I was always told diesels love rpm. They told me lugging the motor will hurt them. I have always kept my trucks in the higher rpm range . Truth be told, I’ve always had a heavy foot and driving semis I never paid for my fuel so it was pedal to the medal ( with in reason) . As far as idling a truck basically , when I started it in the morning for work ,for the most part I never shut the truck off ( more or less)

Wet exhaust marine diesels are better. No DPF or DEF. Why would you need either when they are sucking water from outside the boat, running it through the heat exchanger then dumping it into the exhaust system. This both cools the exhaust and captures any particles in it. a dry stack is no different than a diesel on a truck DPF/DEF required. Josh, I know the old 2 stroke Detroits had a TT option on many of them, TT being tuned turbo which was to make the engines sip fuel at 1800 rpm. Is there any way to set a Cat engine like this?

Paccar specs a fuel saving truck with a 12 speed auto and a crazy axle ratio like 2:64. My last fleet truck had this an ran under 1200 rpm at 70. It did get about 5 percent better fuel economy than the other spec trucks but it was a disaster to drive. Absolutely would not downshift until 900 rpm. The entire truck would shake and rattle and oil pressure about 20 psi at full pull.

13:19, that animation is actualy verry correctly showing what yer conrod will do if you are toooooo rev happy

Mxs 6plus MPG with broke compression Ring's on 2 3 And 4

I have a Mack. If I idled at 650rpm, the engine would consume more fuel than idling at 1000rpm. I don't know why but that is the way it is. At 650, the engine load is at 8%, at 1000 the load goes down to 5% or 4% sometimes.

What an excellnt film. I've never really understood the relation ship between HP and Torque. (where does the 5252 come from? ( I don't doubt it, I just wondered where it comes from.)

Whew! I need a drink now.😄

Farm & construction equipment typically gain better fuel economy than most trucks due to the incredible load.

Could you do a video on max piston speeds and maybe some formulas as well

How does this work with a hydrostatic transmission? Is there an optimal RPM or should it just be run flat-out for maximum flow?

The best RPM to run a diesel is what is recommended by the manufacture turning it too hard will not be good for it, especially if your want the engine to last, well over 1,000,000 miles with good maintenance

13 speed c15 acert old werner tuck 03 ...67/70 mph at 14 to 1500 Loaded 75000+ truck runs great . 4.5 to 5 mpg.

good vid, but hasn't gotten into Volumetric efficiency, which is the root of why peak torque occurs where it does for a particular engine, and why it falls off Volumetric efficiency (VE) is how much (as a percentage) the cylinder gets filled on each stroke... around peak torque is where everything works together and you get maximum cylinder fill between intake and exhaust harmonics, and minimal pumping losses.. If you fall below peak torque RPM, usually you'll get intake reversion since the intake valve doesn't completely close until the piston is somewhere on its way back up for the compression stroke.. On the other hand, if you go much above peak torque RPM, the air can't flow through the valves fast enough to fill the cylinder, and exhaust restrictions (turbo, muffler, etc) start to choke it... you can still make more power for some time after that since you're still taking in more air, but it'll cost you since you're doing a lot of work to do so... At some point, it takes so much work to move the air you can't make any more power with more RPM

Always on the Top. Love your videos. Very informative. Can you help me to find out vibration coming from front. I did all my mechanics told me. New kingpin, bushings, shocks, damper valve, Clutch, couldn't able to find the vibration. Changed couple mechanics. Where is your shop. I have this problem on c15 in my peterbilt 379x. I did overhaul in 2 year ago from cat. I did dyno too from cat. Still same problem. Please help me. Thanks

Work = Force x Distance. Unit is joules. Rate of doing work is joules per second. Unit is Watts, kiloWatts or your old Horsepower 748Watts. Thus the rate of doing work is the force x the rate of distance change. Feet per second (old school) or meters per second. So kW = Force (torque) x distance/ time (rpm).

But at the end if the day- it all depends on what truck It is in/ gears/ and tires- Yiu can have the same truck with a couple changes Amd have 2 very different rpm that max mpg is achieved.. also WhT come into play big time with a lower rev engine..