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How much HP/Torque do you really need?


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This topic is "Soley" for my information/curiosity... PLEASE tap into this conversation to enlighten me, because I am a bit confused..

 

I have spoken to many people on a personal level, and also online about the riggers of hauling a LARGE trailer and what it takes to do so safely, and my conclusions are without a doubt the HDT RV Hauler (ie....Class 7-8 semi trucks)!!

 

NOW, that you owns this beast of a machine that can pull mountains up cliff's, or descent down hills without a single flinch to touch the service brakes, we all understand this is the ULTIMATE vehicle to tow your precious Rig... AT THE LEAST, the vehicles output 400HP/1200lbs of torque, yet I see people that want to buy a truck with 500 and sometimes 600hp with 1800 ft lbs of torque!!

 

I am just assuming, that after a certain amount of HP and torque, it seems to be an overkill of power and torque... Could it just be a "BIG MAN HAS BIG TOOL" game??? Let me be perfectly clear here, I am NO DIFFERENT than anyone here, and I "LOVE" to show that I have a bigger chest than any rooster in the pack at times when applicable, because I have what is commonly known as "testosterone"... And unfortunately, testosterone sometimes makes us (men, and maybe some women) do thing that are seemingly unrealistic, just to make a statement to others, or maybe even make ourselves feel better about the void we are missing in our lives...(LOL).

 

ANYWAY, my point being, by dragging around a 20000lbs (gross) toyhauler, would the engine ( Volvo vnl 670-780 only as an example) with the least HP/torque be adaquate enough?? Just wondering?!?!?!?!

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Try looking at it from this view point.

If it takes 400hp and 1200ftlb of torque to move your 20000lb rig up a 6% grade, do you want to use 100% of the power 100% of the time, or would you rather use 75% of the power and not strain your engine as much by using a higher horsepower and torque engine.

Thank you for your answer as well sir, but if I have a truck that produces 400hp/1200ftlbs of torque, and it takes 100% of the power to climb a 6% grade with a 20000 lbs trailer, then I need a REAL truck because something is Definitely wrong with the one I am driving!!!

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"ANYWAY, my point being, by dragging around a 20000lbs (gross) toyhauler, would the engine ( Volvo vnl 670-780 only as an example) with the least HP/torque be adaquate enough?? Just wondering?!?!?!?!

As has been answered, your question was "least HP/torque", but you won't probably find that 400/1200 in a 780, and probably not a 670 either. Having extra power is ALWAYS a good thing.

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"ANYWAY, my point being, by dragging around a 20000lbs (gross) toyhauler, would the engine ( Volvo vnl 670-780 only as an example) with the least HP/torque be adaquate enough?? Just wondering?!?!?!?!

As has been answered, your question was "least HP/torque", but you won't probably find that 400/1200 in a 780, and probably not a 670 either. Having extra power is ALWAYS a good thing.

Thank you sir, but I have seen these power combinations on both trucks (for example) truckpaper.com... Now, it could have been a misprint or mistake, but that is why I MUST ask these questions, because I simply do not know and only ask the experts that DO know...

 

And you are absolutely right about extra power is always good, because I am all for buying as much truck for as little money myself, but if I am on the hunt for a truck that meets my expectations and requirements 100%, would the lower HP/torque truck have me at a disadvantage, compared to the higher Hp truck towing the same weight, or would the smaller engine be more than adequate??

 

I certainly hope that I am not confusing anyone with my question, simply want to know if the lower HP/torque engine has any disadvantage/ advantages as compared to the larger engine as far as climbing mountains in California, Colorado, Alaska or anywhere, with the same payload..

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Going back to the 'good ole' 60's and the muscle cars, every one knew that displacement was the king, torque was the queen and the horsepower was the court jester.

So 20,000 pound real or "theoretical" toy hauler will be very happy with a 12-14 liter diesel producing 14-1,600 foot-pound of torque. Up hills. down hills and actually will get a decent fuel mileage on flats because the engine will loaf (actually idle while pulling).

The smallest engine in the class 8 trucks will be around 11 liters, many folks had/have trucks with those engines and these are quite adequate, might have to do a little more shifting in the mountains.

Can you pull 20,000 pound trailer, with smaller diesels, sure you can, right down to the 7 liter jobs you will find in MDTs and pickup trucks. Diesel engines have a tremendous low RPM (starting) torque and a 7 liter engine will definitely get a 20,000 pound trailer going and even get it to 60 mph on a flat, don't expect to maintain that speed even up a small hill. And your mileage will be worse than that of a 14 liter engine because it will be screaming it's head off and spend lots of time in lower transmission gears.

I found a perfect visual representation of a 20,000 pound trailer pulled by a 7 liter truck.

2902955090096176628IHnXeJ_ph.jpg

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Unless you are ordering a new truck, the engine size will not have much of a factor in the cost of a used truck.

 

Likewise, the intelligence of the Engine Computer Unit (ECM), the engine will use the amount of fuel it needs to to do the job. I.e. A 450 HP engine will have the same fuel consumption as a 600 HP engine for an equal load.

 

The importance in a truck purchase is not the engine nor the rear end ratio. The transmission is a strong factor since you want an automatic transmission unless you think your are smarter than the transmission computer (you are not).

 

The brand/model will matter depending on your cab space requirements.

 

The next factor in the physical condition of the truck. When you find a truck in great condition, whatever engine it has really won't matter.

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Going back to the 'good ole' 60's and the muscle cars, every one knew that displacement was the king, torque was the queen and the horsepower was the court jester.

So 20,000 pound real or "theoretical" toy hauler will be very happy with a 12-14 liter diesel producing 14-1,600 foot-pound of torque. Up hills. down hills and actually will get a decent fuel mileage on flats because the engine will loaf (actually idle while pulling).

The smallest engine in the class 8 trucks will be around 11 liters, many folks had/have trucks with those engines and these are quite adequate, might have to do a little more shifting in the mountains.

Can you pull 20,000 pound trailer, with smaller diesels, sure you can, right down to the 7 liter jobs you will find in MDTs and pickup trucks. Diesel engines have a tremendous low RPM (starting) torque and a 7 liter engine will definitely get a 20,000 pound trailer going and even get it to 60 mph on a flat, don't expect to maintain that speed even up a small hill. And your mileage will be worse than that of a 14 liter engine because it will be screaming it's head off and spend lots of time in lower transmission gears.

I found a perfect visual representation of a 20,000 pound trailer pulled by a 7 liter truck

2902955090096176628IHnXeJ_ph.jpg

OMG!!! That was the PERFECT explanation, thank you sir...
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Unless you are ordering a new truck, the engine size will not have much of a factor in the cost of a used truck.

 

Likewise, the intelligence of the Engine Computer Unit (ECM), the engine will use the amount of fuel it needs to to do the job. I.e. A 450 HP engine will have the same fuel consumption as a 600 HP engine for an equal load.

 

The importance in a truck purchase is not the engine nor the rear end ratio. The transmission is a strong factor since you want an automatic transmission unless you think your are smarter than the transmission computer (you are not).

 

The brand/model will matter depending on your cab space requirements.

 

The next factor in the physical condition of the truck. When you find a truck in great condition, whatever engine it has really won't matter.

LOVED that answer sir!!! However, I will have to differ on your opinion about me not being smarter than the transmission... (Well, after considering and thinking it through, you might be right about that)!!!! "Laughing"

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Keep in mind a repair shop can always turn up the horsepower using just a laptop computer. There are other things they can change while they have access to the trucks computer like shift points, top speed, warning buzzers, shut down alarms, ect. I asked my local Cummins shop how much to turn mine up and change other parameters and it's $200. That is if I have the password to the ECM, which I do. They said the components like the size of the turbo and the trans itself are the limiting factors on how much they can turn it up. When you buy your truck ask them if they have the passcode for the ECM. I think Volvo wants $100-200 for it??

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LOL - Wow, you talk J1939 data? On these automated Trans's the ECM and TCM have conversations;

 

Engine - coming up on 1500 rpm and not fueling hard

Trans - OK, I can do a shift, back off on the fuel

Engine - OK trans, fueling down and ready for you to do your thing

Trans - OK clutch open back off the go pedal to 1000 rpm - Doing it now

Engine - OK I'm at 1000rpm

Trans - OK - I need 950 Rpm on the flywheel

Engine - OK, it's there

Trans - cool, clutch closed, pour the juice to it and lets go baby.

Trans - Hey DID, bring up 6th gear on the display and let that mouth breather know we're in 6th gear.

Engine - DID, tell him that we're running at 1000 RPM and sucking 12 gallons of fuel per hour. Also flash that yellow light thingy that tells him to lighten on of the go fast pedal and we'll get bonus points for economy, while your at it.

 

......

 

Engine - Hey DID, Flash this mouth breather, he's coming up on Mach 1.2, He keeps this up, DOT is gonna flash my programming and have us back at 55 again.

 

 

Just cause you have the power, doesn't mean you have to use it. Then we come to those long uphill grades and all the heavies are down in 5th and grinding up the hill in the right lane. You feed some more power to the beast and roll right on past at 55 - 60. As Phoenix said in #8, "Let the torque set you free, young Jedi"

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Your question is better answered by breaking it into two separate questions.

 

1. Is a basically equipped power train on a 670 or 780 Volvo, sufficient to haul a 20,000 pound rv trailer or toyhauler?

 

Yes. The rv with a gross weight in the neighborhood of 20,000 pounds is also in the neighborhood of what a lot of semi trailers weigh, empty.

 

Granted, a 650 horsepower engine will pull that load much quicker and faster up a steeper grade, but a D13 Volvo engine, that can run between 375 and 500 hp, will still be overkill for most people. Unless you have an unlimited drive tire budget, then you can never have enough horsepower/torque.

 

2. Why would someone spec a truck out above 400 horsepower if that would be adequate?

 

The legitimate reason is in the case of someone speccing out a truck for heavy haul where the gross weight of the truck will be 120,000pounds, or more.

The other reason is for folks who want to be able to haul any load up any hill at any speed. Or they just love to have that ability. The tire budget applies here as well.

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An honest answer from an ex HDT owner....

As most of us true "Cowboy HDT'rs" are/were their is no limit on how much is too much :) It's just a motor head mentality that I have had all my life..

When I was farming, I used a ~340 hp tractor when a my 100 hp, or others I had would have been just fine....

(Oh, and yes I did buy bigger equipment for it...but didn't really need any of it)

Cheers,

Bob

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Well, since I just spec'ed a new truck and could have ordered a wide variety of hp/tq spec's I went with the highest rating (500/1850) I could get in a D-13 engine. I live in the west and am in the mountains quite a bit. One of the other considerations spec'ing this truck was gear ratio which I went with 2.67 ratio. The Eco-torque engine spec makes good power down to 950 RPM. The truck just idles down the road and is very quiet at low rpm of about 1150@65 mph. This combination of high power a high gear ratio works very well but would not want any less in the mountains.

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I cannot speak of other HDT's, but I tow with a 2008 Volvo 780 with 16 liter engine. It gets about 19 mpg (at 65mph) deadheading and 11 mpg towing (at 60mph).

 

I use to tow with a 2008 Ford F550 with a 6.4 liter engine. And, at the same speeds as above, The F550 got 11mpg deadheading and about 6mpg towing. So, the Volvo fuel economy, with an engine almost three times as large as the Ford, is almost two times better than the F550.

 

I will leave it to the folks smarter than me to explain the why.

 

Bottom line, better to have bigger and, for me, the fuel economy got better bigger :rolleyes:

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It is also a little bit about availability. Since a good portion of these Class 8's are spec to haul 80000#, the majority have the larger HP and Torque specs. The good ones that have the smaller motors seem to just not be available as readily for this groups needs. As other have said, there are so many other factors in looking for a truck, that having one with too large of a motor is usually not a deterring factor.

 

For many it is more about the size (condo height or not), transmission (2 pedal, 3 pedal, stick) how well it was maintained (records available), mileage, cleanliness (non smoked in, not rusty, livable), etc...

 

When you put more limitations (HP, size of motor, gear ratio, color, amenities like refrigerators stocked with Dr. Pepper, exact WB length, a certain brand of tires) it makes it hard to find the exact truck.

 

Each of us has to decide what it critical and most important to them when searching for a HDT, but we also need know what our own limitations are, so we know what we can do to modify a potential truck to make it our ideal one. I haven't heard of anyone changing engines just to get a lower HP or Torque number and I know I wouldn't do it!

 

Dave

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Keep in mind a repair shop can always turn up the horsepower using just a laptop computer. There are other things they can change while they have access to the trucks computer like shift points, top speed, warning buzzers, shut down alarms, ect. I asked my local Cummins shop how much to turn mine up and change other parameters and it's $200. That is if I have the password to the ECM, which I do. They said the components like the size of the turbo and the trans itself are the limiting factors on how much they can turn it up. When you buy your truck ask them if they have the passcode for the ECM. I think Volvo wants $100-200 for it??

That is very informational! All of these answers are piling up in my little black book... With all of these great answers, this is a "fail safe" way to buy, inspect, and know exactly what I want!! Question for you AllenF, does size matter to you??? (ENGINE SIZE)!!!!

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LOL - Wow, you talk J1939 data? On these automated Trans's the ECM and TCM have conversations;Engine - coming up on 1500 rpm and not fueling hardTrans - OK, I can do a shift, back off on the fuelEngine - OK trans, fueling down and ready for you to do your thingTrans - OK clutch open back off the go pedal to 1000 rpm - Doing it nowEngine - OK I'm at 1000rpmTrans - OK - I need 950 Rpm on the flywheelEngine - OK, it's thereTrans - cool, clutch closed, pour the juice to it and lets go baby.Trans - Hey DID, bring up 6th gear on the display and let that mouth breather know we're in 6th gear.Engine - DID, tell him that we're running at 1000 RPM and sucking 12 gallons of fuel per hour. Also flash that yellow light thingy that tells him to lighten on of the go fast pedal and we'll get bonus points for economy, while your at it.......Engine - Hey DID, Flash this mouth breather, he's coming up on Mach 1.2, He keeps this up, DOT is gonna flash my programming and have us back at 55 again.Just cause you have the power, doesn't mean you have to use it. Then we come to those long uphill grades and all the heavies are down in 5th and grinding up the hill in the right lane. You feed some more power to the beast and roll right on past at 55 - 60. As Phoenix said in #8, "Let the torque set you free, young Jedi"

Great answer Bill B! I'm starting to understand a LOT more about how diesels work.. And if I am assuming correctly, even the lowest HO engine could pull the 20000lbs rig up the hill big at speed without resistance, hindering or labor inn the engine too much.. I am assuming that even an engine with 355HP and 1200ftlbs Torque will still chug past others doing 55MPH at low RPM's... When asking my original question, this is what the information I was driving for.. Thank you sir!!!

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Your question is better answered by breaking it into two separate questions.

1. Is a basically equipped power train on a 670 or 780 Volvo, sufficient to haul a 20,000 pound rv trailer or toyhauler?

Yes. The rv with a gross weight in the neighborhood of 20,000 pounds is also in the neighborhood of what a lot of semi trailers weigh, empty.

Granted, a 650 horsepower engine will pull that load much quicker and faster up a steeper grade, but a D13 Volvo engine, that can run between 375 and 500 hp, will still be overkill for most people. Unless you have an unlimited drive tire budget, then you can never have enough horsepower/torque.

2. Why would someone spec a truck out above 400 horsepower if that would be adequate?

The legitimate reason is in the case of someone speccing out a truck for heavy haul where the gross weight of the truck will be 120,000pounds, or more.

The other reason is for folks who want to be able to haul any load up any hill at any speed. Or they just love to have that ability. The tire budget applies here as well.

YES, YES, That's my answer!!!! WHEW!!!! I was stating to think "maybe I should stop asking these stupid questions" but my questions to the masses and your answers seem to like each other !!!! Thanking EVERYONE soooo much!! NOW, wait till I get my rig and trails and see you all at one of the rallies, you are going to have to hide from me, just to shut me up!!! (Laughing). LOVING THIS!!

 

Again, Thank you Vegasflyer!!!

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An honest answer from an ex HDT owner....

As most of us true "Cowboy HDT'rs" are/were their is no limit on how much is too much :) It's just a motor head mentality that I have had all my life..

When I was farming, I used a ~340 hp tractor when a my 100 hp, or others I had would have been just fine....

(Oh, and yes I did buy bigger equipment for it...but didn't really need any of it)

Cheers,

Bob

I am no different than you sir, as many have already answered in here that "it is the fact that knowing you have that much power, can make any situation THAT much easier and enjoyable"... There is NOTHING wrong with a little extra " reserve" insurance...LOL

 

Thank you sir...

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Well, since I just spec'ed a new truck and could have ordered a wide variety of hp/tq spec's I went with the highest rating (500/1850) I could get in a D-13 engine. I live in the west and am in the mountains quite a bit. One of the other considerations spec'ing this truck was gear ratio which I went with 2.67 ratio. The Eco-torque engine spec makes good power down to 950 RPM. The truck just idles down the road and is very quiet at low rpm of about 1150@65 mph. This combination of high power a high gear ratio works very well but would not want any less in the mountains.

I think that is what I am going for as well!! I am trying to find a truck with your specs.. That just plain make soooo much sense!! BTW, I have been watching you online with your beautiful truck and trailer set up, and I will say that you should start a topic about VERY COOL THINGS!!!! You sir have a VERY nice rig combination! Congratulations to you and EVERYONE that already has an HDT RV hauler... Not only are you guys/ladies smart, but you bring the pride and class back into 5th wheel ownership!!!

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I cannot speak of other HDT's, but I tow with a 2008 Volvo 780 with 16 liter engine. It gets about 19 mpg (at 65mph) deadheading and 11 mpg towing (at 60mph).

 

I use to tow with a 2008 Ford F550 with a 6.4 liter engine. And, at the same speeds as above, The F550 got 11mpg deadheading and about 6mpg towing. So, the Volvo fuel economy, with an engine almost three times as large as the Ford, is almost two times better than the F550.

 

I will leave it to the folks smarter than me to explain the why.

 

Bottom line, better to have bigger and, for me, the fuel economy got better bigger :rolleyes:

Sir, you ARE the smarter folks!! You own something that is economical, powerful, AND safe!! You did exactly what (as you claim) the smarter folks did, so bravo for you.. Explaining to me how things works is one thing, but actually applying the same principal as what they are explaining to me seems to work just as well.. I'm a bit suprised with the 19mpg@65 MPH (deadhead), and 11mpg towing because those are GREAT numbers... Would you care to share Your formula on how you accomplished this? Rear end ratio, engine type,mthat are you towing?? Because with those numbers, I am more than certain a LOT of us would LOVE to tap into that information, and incorporate some of your specs!!! Thank you Dromi!!!

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It is also a little bit about availability. Since a good portion of these Class 8's are spec to haul 80000#, the majority have the larger HP and Torque specs. The good ones that have the smaller motors seem to just not be available as readily for this groups needs. As other have said, there are so many other factors in looking for a truck, that having one with too large of a motor is usually not a deterring factor.

 

For many it is more about the size (condo height or not), transmission (2 pedal, 3 pedal, stick) how well it was maintained (records available), mileage, cleanliness (non smoked in, not rusty, livable), etc...

 

When you put more limitations (HP, size of motor, gear ratio, color, amenities like refrigerators stocked with Dr. Pepper, exact WB length, a certain brand of tires) it makes it hard to find the exact truck.

 

Each of us has to decide what it critical and most important to them when searching for a HDT, but we also need know what our own limitations are, so we know what we can do to modify a potential truck to make it our ideal one. I haven't heard of anyone changing engines just to get a lower HP or Torque number and I know I wouldn't do it!

 

Dave[/quote

 

I'm laughing at your last comment, because that certainly would NOT be what I would want either.. What worries me Dave is when I look online at trucks, I am just Leary about some of the trucks I see.. "For example" a 2006 Volvo with a D-11 with only 600000 miles on it... It could be true, but I am just worried that some of these engines have been turned over and worn out.. An unsuspecting person could look at this as a very well taken care of engine, when in fact the engine could be on its last leg, or has had a significant around of work done to is, and is driven hard!!! (Im sorry, I am getting too deep into another subject), but you are right sir, get what you can get, and be happy!! I'm listening to Ya!!!! (Smile). Thanks Dave...

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