Diesel engine power

[Hpymils]

Is a 300hp diesel sufficient for a 36/37 foot motor home? Will a 300hp lug down on hills?

[Gjac]

hooligan wrote:

Crespro wrote:

The torque/HP question arises periodically. My question is: do all of these engines produce rated torque at the typical 1,600 RPM? What is the difference in the torque/RPM curves?

Torque and rpm values vary greatly even among the same engines. My ISB 260 produces 550 ftlbs torque at 1900rpm while another version of that same engine is available with 260HP, 660Ftlbs at 1600rpm.

ISB Engine ratings

I notice in the ISB chart posted that the ISB 225 has 225hp and 605 ft lbs @ 1600 rpm and the ISB 225 has 225 hp and 520 ft lbs @ 1600 rpm. How can these engs have the same HP and different torque values at the same rpm? Is this a typo or am I not understanding something more basic.

[RayChez]

Manufactures of coaches will install diesel engines by the weight of the coach. You will not find a 600 hp engine on a 36 foot coach. If that smaller coach weigh's 24-27K lbs you will find that all manufacturers install ISB Cummins. If the coach weigh's around 34K they will install ISC Cummins engine, and if it is up close to the 40K lb weight they will install the ISL Cummins engines.
Now if you go real big like a Newell or Prevost, them coaches are real heavy at close to 50K lbs so they install big powerful Volvo, DD engines to move all that weight. You are not going to see a heavy coach with a ISB or even ISC Cummins.
So it is nice to have lots of power, but you probably would have to special order the coach to accommodate your wishes.

[JetAonly]

bluwtr49 wrote:
Regarding the "lugging down", Cat recommends that a diesel be allowed to "lug" for the best efficiency. I think they define lugging as letting it the rpm drop to the peak torque speed and only downshift if that rpm can not be maintained. To do this with the Allison I just keep it in the Mode setting and the performance is amazing.

However, a caveat is on extended grades running at peak torque the engine RPM is too low for maximum cooling so a downshift is necessary if coolant temp becomes excessive.

In other words, don't worry about "lugging" it.

Yep!

Cummins, for example, defines lugging as the application of full throttle below torque peak.

OP, the answer is a definite maybe. We need more info as to the vehicle and towing to compare it to the real world.

Enough being a relative term directly related to the size of your wallet.

[hooligan]

Crespro wrote:

The torque/HP question arises periodically. My question is: do all of these engines produce rated torque at the typical 1,600 RPM? What is the difference in the torque/RPM curves?

Torque and rpm values vary greatly even among the same engines. My ISB 260 produces 550 ftlbs torque at 1900rpm while another version of that same engine is available with 260HP, 660Ftlbs at 1600rpm.

ISB Engine ratings

[bluwtr49]

Regarding the "lugging down", Cat recommends that a diesel be allowed to "lug" for the best efficiency. I think they define lugging as letting it the rpm drop to the peak torque speed and only downshift if that rpm can not be maintained. To do this with the Allison I just keep it in the Mode setting and the performance is amazing.

However, a caveat is on extended grades running at peak torque the engine RPM is too low for maximum cooling so a downshift is necessary if coolant temp becomes excessive.

In other words, don't worry about "lugging" it.

[Peralko]

Another issue is the turbocharger on diesel engines, which keeps power at high altitudes whereas gas engines lose significant power at altitude.

[ferndaleflyer]

Since I have one of each this is what I see towing my trailer.

The 330 Cummins 325hp in the 38ft DP slows to about 50--55mph on long steep grades.

The 500hp in the 45ft barely slows towing the same trailer up the same grades. But even at that HP it still slows some. More weight!

[mci7]

Total correct, it is a matter of weight vs hp & torque, My setup is a 30,000 lb with the Cummins ISM500 & 1550 ft lb torque, hills are not an issue, I pass everyone going up, and everyone passes me going down, I do laugh a lot.
Years ago, I drove truck, found quick the mountain travel and decided if/when I bought a motor home, it would have enough power to get it done.
Dave M

[Golden_HVAC]

I have a factory engine horsepower rating of only 225 HP at 3,600 RPM with my 97 460" V8 in my Bounder. It will slow to about 45 on a 6% grade in second gear at 4,000 RPM in second gear.

My buddies 350 HP 40' DP that is about 26,000 pounds does not do as well on the mountain grades. It is much heavier than my RV, by about 9,000 pounds.

When I took my motorhome to Sequoia National Park, I can remember doing about 45 up the hill, and taking the curves at a slightly slower speed, I could pick up speed even climbing the hill. With the DP, I was not able to get above about 35 MPH, because it would not stay in 4th gear without bogging down, and it would redline in 3rd gear around 38 MPH, so I was stuck going slower in the DP.

Fred.

[wolfe10]

Crespro wrote:

wolfe10 wrote:
Actually HP alone does not answer the question.

There are Cummins B's with 300 HP and 6XX lb-ft torque
There are Cat 3126's with 300 HP and 860 lb-ft torque
There are Cummins C's with 300 HP and 960 lb-ft of torque

They are NOT the same.

The other part of the equation is loaded coach weight with toad.

The torque/HP question arises periodically. My question is: do all of these engines produce rated torque at the typical 1,600 RPM? What is the difference in the torque/RPM curves?

The larger the engine (actually, the longer the stroke), the lower RPM for peak torque. So, peak torque could be at 1100 RPM or 1800 RPM.

[Crespro]

wolfe10 wrote:
Actually HP alone does not answer the question.

There are Cummins B's with 300 HP and 6XX lb-ft torque
There are Cat 3126's with 300 HP and 860 lb-ft torque
There are Cummins C's with 300 HP and 960 lb-ft of torque

They are NOT the same.

The other part of the equation is loaded coach weight with toad.

The torque/HP question arises periodically. My question is: do all of these engines produce rated torque at the typical 1,600 RPM? What is the difference in the torque/RPM curves?

[Gjac]

Hpymils wrote:
Is a 300hp diesel sufficient for a 36/37 foot motor home? Will a 300hp lug down on hills?

Compared to what? If you compare it to a gas V-!0 with 362 HP that weights 16,000 lbs and the 300 hp DP weighs 30,000 lbs I would say it will lug (be much slower on a hills).

[bshpilot]

Hpymils wrote:
Is a 300hp diesel sufficient for a 36/37 foot motor home? Will a 300hp lug down on hills?

depends on the Transmission & RearEnd gearing.
IMO more (hp, tq & transmission) is better !

[RayChez]

There are many 36 foot coaches with 300 hp diesel engines. 36' diesel coaches probably will weigh around 27K lbs. So I would say yes it is plenty power to move that much weight up hills.

But one thing you have to learn when driving those coaches is to always keep an eye on the tachometer and if it starts to lug down, do not hesitate to shift to a lower gear and keep a certain rpm.