Community Forums

Miserabull · 09-12-2006, 12:27 PM

I am looking at a 38 foot Expedition with a 300 HP Cat Engine, will that be enough power for that size of motorhome.

Miserabull · 09-12-2006, 12:27 PM

I am looking at a 38 foot Expedition with a 300 HP Cat Engine, will that be enough power for that size of motorhome.

GStream40 · 09-12-2006, 02:36 PM

What I was told a few years ago from an diesel owner was you take the HP of the engine and multiply that times 100 and the equals the amount of weight the coach could weight for that engine.

300hp X 100 = 30,000 lbs. max coach weight

I don't know how acturate it is, but has worked for me.

Anyone else ever heard of this?

Ron

Miserabull · 09-12-2006, 04:46 PM

Thank you, I had not heard that before.

jdoc · 09-13-2006, 02:39 AM

My Bounder has the same engine. So far so good no problems at all.

Bob (WA0MQE) · 09-16-2006, 04:57 AM

It depends on how much weight you plan to carry, and the weight of your tow vehicle as well as the typical locations you plan to travel with this weight.

It's not so much the 300HP you should be concerned with, it's the torque. If you typically stay in the lower elevations and don't drive on a whole lot of steep hills then you will probably be happy with it. If, however you intend to make a lot of trips in the higher elevations of the Western US, you will probably be disappointed.

Bob (WA0MQE) · 09-16-2006, 05:06 AM

I meant to add my situation to my first response, but I hit the button to quickly, so I'll add it here.

As can be seen by my signature I have a gas moho which has the 8.1 L GM engine. It's a big engine that develops 340 HP at 455 lbs of torque, but it's not enough for a 26,000 lb motorhome including the toad.

A lot of fellas have done after market performance enhancements to there same engines and have posted very good results in both improved gas mileage and pulling power, but most of these, according to their signatures, live in much lower elevations as well as flat terrain. Mine however, apparently due to the elevation here in Colorado hasn't done that much for improvement in both mileage or power. If I had it to do over again I'd wait till I could afford at least a 350 or better still 400 HP diesel, one with lots of low-end torque.

JRP · 09-16-2006, 05:28 AM

Miserabull,

I assume this is a CAT C7 engine and if so, that same exact engine can be configured for 300, 330 or 350 HP by propietary changes to the CAT electronic engine control module. As correctly pointed out the torque is just as important as the HP, and all C7's give you 860 ft-lbs of torque regardless of their HP setup. So if you find the 300 HP is not quite enough for the weight you carry/pull, you would have the option of going to an authorized CAT engine shop and having it upgraded to 330. How much that costs usually depends on other effected systems which may also need to be upgraded to handle the increased heat of producing more HP.

Jim

Catdave · 09-18-2006, 07:45 AM

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by GStream40:
What I was told a few years ago from an diesel owner was you take the HP of the engine and multiply that times 100 and the equals the amount of weight the coach could weight for that engine.

300hp X 100 = 30,000 lbs. max coach weight

I don't know how acturate it is, but has worked for me.

Anyone else ever heard of this?

Ron </div></BLOCKQUOTE>

This formula is usually promoted by those who do not understand the affect torque has on moving a given load. By this simplistic theory, a 5.9L Cummins with 300hp & 600 lbs./ft. torque will haul 30,000 lbs as well as a 300hp Cat with 860 lbs./ft. torque. Needless to say this isn't likely to happen.

So as mentioned- don't just look at hp, look at torque as well.

BTW- having driven several Expeditions with the 300hp C7 engine I found the performance more than acceptable.

alvinc · 09-18-2006, 10:17 AM

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Miserabull:
I am looking at a 38 foot Expedition with a 300 HP Cat Engine, will that be enough power for that size of motorhome. </div></BLOCKQUOTE>I am curious as to how one would determine whether the engine is "big enough"? This is a very subjective subject. Is there a minimum speed that you want to achieve on flat ground? On a 6% hill?

Do you live and play in the Eastern US or Western US. The east doesn't have as many steep, or as long, grades as the West. Only if you live out West would a bigger engine be a plus. If you live in the Eastern US and occasionally visit out west, spend your money on something else.

Unless you are commuting up and down steep grades, the amount of time lost to slowing down will be maybe 15-60 minutes per day at most.

moisheh · 09-19-2006, 10:00 AM

Catdave: I must disagree. Begore we bought our Bounder DP I drove the new Cat C7 300 HP and thought something was wrong. It was gutless. Drove 2 more and they were the same. Bought a one year old with the 5.9 Cummins and we couldnt be happier. I would do a 1/4 mile test with any Bounder Cat.

Moisheh

Catdave · 09-19-2006, 11:39 AM

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by moisheh:
Catdave: I must disagree. Begore we bought our Bounder DP I drove the new Cat C7 300 HP and thought something was wrong. It was gutless. Drove 2 more and they were the same. Bought a one year old with the 5.9 Cummins and we couldnt be happier. I would do a 1/4 mile test with any Bounder Cat.

Moisheh </div></BLOCKQUOTE>

Are the weights comparable between the two coaches?
If not, there's your answer.
If so, then you need to recalbrate the "seat of your pants" because I've driven both and there is no mistaking which engine has 860 ft. lbs. torque and which one has 600.

But as they say- performance is subjective...

GStream40 · 09-19-2006, 04:38 PM

Here is a link that explains the "torque and horsepower" and how it relates to the motorhome.
Motorhome Advice

At the bottom of the article is a reference as follows:
"A good rule of thumb when planning a coach load is you should have a minimum of 10 horsepower for every 1000 pounds of coach weight you want to move. Remember your tow vehicle should be in the total weight equation, too."

Maybe this will help explain the torque VS horsepower.

Ron

Catdave · 09-19-2006, 05:14 PM

Good link, GStream.
Again, however, for motorhomes I disagree with the blanket formula of 10hp per 1000 lbs. coach weight, and here's why:
(From a post I made on another board.)

I think it's important to remember that when someone asks for a power recommendation in a MH, we should base our recommendations on real world conditions, not theoretical models. For example, if you woke up tomorrow with a 300hp 5.9L ISB in the place of your 300hp Cat (in other words- all things being equal) in your 30,000 lb. motorhome, you'd notice the difference at the first application of the throttle. It would feel sluggish on acceleration, climb hills slower, and overall the experience would be negative. Yes, you'd still be able to cruise at 60 mph on flatlands just the same as before, but any condition requiring increased power would show a marked decrease in performance, even though both engines produce 300 horsepower.
Then we could transplant a 300 hp ISC in the place of the 5.9L and see what kind of performance it would render. I believe you'd see a marked increase in performance over the 5.9L, yet it too has only 300 horsepower.

The coach weighs the same, we have the same transmission, gearing, tires, aerodynamics, etc. and all the engines have 300 horsepower.
Why then, does one engine outperform another?