Gas vs Diesel (I've read the FAQs!!)

[ZagiFlyer]

Hello to All,

We *still* have the Thor Jazz in my sig, and it's still a going concern, but the wife is up for a change and "we" are wondering if a Class A would fit the bill. Many of our trips are long-range and we'd like to be comfortable driving cross-country -- my daughter has informed me that the back seat of an extended cab is not making her back happy on 6, 8, 12 hour drives.

Keeping in mind that we're coming from a 5th-wheel towed by a 6.0L gasser, my wife is under the impression that a DP will fly up the Grapevine (6% grade) at 50-60 mph. Is this true? I wouldn't expect it, since the HP/torque required to move 26,000 lb up a 6% grade at 50 mph would be enormous.

I've read the FAQs and searched the forums, but I didn't find anything specific enough so here is my question:

Thinking along lines of the Grapevine or other steep/long grades:

• At what speed are you 36-40 ft. DPs getting up steeper grades
• At what speeds are you 36 ft. gas Class A's getting up steeper grades?

For comparison, my rig gets us up the Grapevine at about 35 mph, but it's struggling mightily at 4400 RPM.

I need to set her expectations realistically if I am to acquire any semblance of domestic tranquility when we upgrade.

Thanks!

[OhhWell]

Bruce Brown wrote:

OhhWell wrote:

Bruce Brown wrote:

OhhWell wrote:

Bruce Brown wrote:

Daveinet wrote:

Bruce Brown wrote:
Not the Grape Vine, but Rt 26 out of Johnson City, Tn;
2000 V10 gasser MH - brought to it's knees, 30 MPH tops
2003 DP w/ Cat 3126, 330HP/860 TQ - 55 MPH
...
If you're ready for a DP skip the HP number and look at the torque.

I'd like to see you reconcile your statements with the post from Greyhost above. My guess is you have not considered the weight of either coach, or the altitude. An old V10 has serious breathing problems, which will be exacerbated by any kind of altitude. No doubt that is a big factor, so you argument of torque doesn't hold water. (never mind that it defies physics)

I have no idea why he was limited to 50 MPH in his diesel - ours does not.

As to the rest, I'm offering real world expirence, not a physiscs class. If it makes you feel better to say I'm wrong then OK, make yourself happy.

If you want to buy a low torque engine go ahead, I won't.

We've owned gassers and diesels in both our MH's and pickups. Gas has it's place, but when it comes to hard work I'll take a diesel every time, and the bigger the better.

Nothing wrong with loving a high torque engine as they make for a very pleasant driving experience. When you say ignorant things like ignore the HP number, it's all about torque; unfortunately, you are doing a disservice in addition to being just plain wrong.

Ask yourself;

Do you want a 300HP/600#/ft diesel or do you want a 300/950#/ft diesel?

Me? Ignorant as I may be I'm skipping the HP number and going for more torque.

Take a look at the torque curves and you'll know why. :W Where an engine makes power is just as important as how much it makes. A low torque diesel just can't offer what a high torque one can. And until you've owned both (we have) you just won't understand.

You gotta be kidding me right? You expect anyone with a good sense of reasoning to take you seriously after that?

besides, it doesn't usually work out like that. Lets take the Cat 3126 that is offered in different power levels from 300 to I think 350 HP but the TQ rating is the same. Which would you take? Would you flip a coin since they should all do about the same?

I have driven High TQ , Low HP engines and vice versa. I completely understand how a high TQ engine just feels more powerful and is fun to drive, I ALSO understand how it runs out of steam when you have exceeded the HP it has available. You can also increase TQ at the wheels simply through gearing. You can't increase HP.

You are dead set on believing what you want to believe as dead wrong as it may be. The good thing is most modern diesels have plenty of HP DUE to their high torque abilities.

Of course it works that way. Look at the Cummins engine family.

Pre 07 EPA they offered the ISB in a 300HP/600lb/ft configuration and the ISC in a 300HP/950lb/ft configuration.

The ISC had more available torque through a wider part of the powerband than the ISB had at it's peak, even though they were the same peak HP.

Like I said - where it makes its power is as important as how much peak power it makes. More available torque usually means much more broad torque curve.

In your Cat example, how they got more HP without raising the torque is simple - they spun it faster.

Remember, HP is determined by torque, not the other way around. ((TorquexSpeed)/5252)

Having said all of this, sure, if we all only ever drove at peak HP then sure, it wouldn't be a big deal, but we don't - we drive through a wide variety of conditions and RPM ranges, so in the real world I'm looking for more torque - the HP part will take care of itself.

Ahh, I didn't think you were comparing engines from different lines, in that case, the ISC is de-tuned to 300 hp. What I thought was utterly ridiculous was backing up your statement about ignoring the HP number by using an example of two engines with the exact same horsepower... well, DUH! You would have seemed more reasonable if you had used the argument about not really needing the most out of the engine (HP) in most driving anyway so in that case TQ might be ore important. Beside going round and round again, it also kinda acknowledges the FACT that HP is the amount of work over TIME that the engine can produce. I know TQ influences HP. They are all tied together.

Also, as Dave stated, Torque can be multiplied through gearing, HP cannot. I have stated that time and time again in these silly bickering matches and it is never really acknowledged by folks on your side of the fence so to speak.

It shouldn't but GAS vs Diesel always runs right along with HP vs TQ. The are both measurements of the power plant. There are gas engines with more TQ than HP. I have owned and driven 2. I completely get it. It's NICE to have a lot of torque. It's nice all the way up till you run out of HP and then you are out of steam.

[phnguyk]

Daveinet wrote:

OhhWell wrote:
That's do-able. I can live with 45mph on a 6-7. I didn't have any trouble keeping my 60 mph cruising speed on 4%. Well, the engine was roaring but I kinda like the sound.

If you like the sound, come ride with me up a 6% grade @ 80 mph towing my Jeep :B

BTW: When one compares 2 different engines with the same HP and different torques, there is an assumption that both units are optimally geared for the desired speed. If not then all bets are off.

Also something else to keep in mind, as one hits high altitudes, a turbo is able to compensate for the lack of air density by just cramming more air in. If not for the turbo, a diesel would be much worse than gas at high altitudes. I'm waiting for a large format turbocharged gas truck engine. Gas engines run hot, so that is the real difficulty running a turbo on a heavy duty gas engine.

I disagree with the "gas engines run hot" I've never hit 200 degrees, average 190, which I think is close to norm for a diesel too.

[Daveinet]

One small problem, you can always create any torque characteristics you want by gearing. You can not create HP by gearing.

[daytripper63]

I went from a gas class A to a 5th wheel to a 40ft DP class A and the DP does 45-55 over the Grapevine. The biggest difference for us in a DP class A is the comfort compared to sitting in my truck and hearing the motor for hours and hours on long trips, the DP with air ride and the motor is in the back, the ride and comfort is nice and I don't have to stop every 45minutes for someone to go to the bathroom etc

[Bruce_Brown]

OhhWell wrote:

Bruce Brown wrote:

OhhWell wrote:

Bruce Brown wrote:

Daveinet wrote:

Bruce Brown wrote:
Not the Grape Vine, but Rt 26 out of Johnson City, Tn;
2000 V10 gasser MH - brought to it's knees, 30 MPH tops
2003 DP w/ Cat 3126, 330HP/860 TQ - 55 MPH
...
If you're ready for a DP skip the HP number and look at the torque.

I'd like to see you reconcile your statements with the post from Greyhost above. My guess is you have not considered the weight of either coach, or the altitude. An old V10 has serious breathing problems, which will be exacerbated by any kind of altitude. No doubt that is a big factor, so you argument of torque doesn't hold water. (never mind that it defies physics)

I have no idea why he was limited to 50 MPH in his diesel - ours does not.

As to the rest, I'm offering real world expirence, not a physiscs class. If it makes you feel better to say I'm wrong then OK, make yourself happy.

If you want to buy a low torque engine go ahead, I won't.

We've owned gassers and diesels in both our MH's and pickups. Gas has it's place, but when it comes to hard work I'll take a diesel every time, and the bigger the better.

Nothing wrong with loving a high torque engine as they make for a very pleasant driving experience. When you say ignorant things like ignore the HP number, it's all about torque; unfortunately, you are doing a disservice in addition to being just plain wrong.

Ask yourself;

Do you want a 300HP/600#/ft diesel or do you want a 300/950#/ft diesel?

Me? Ignorant as I may be I'm skipping the HP number and going for more torque.

Take a look at the torque curves and you'll know why. :W Where an engine makes power is just as important as how much it makes. A low torque diesel just can't offer what a high torque one can. And until you've owned both (we have) you just won't understand.

You gotta be kidding me right? You expect anyone with a good sense of reasoning to take you seriously after that?

besides, it doesn't usually work out like that. Lets take the Cat 3126 that is offered in different power levels from 300 to I think 350 HP but the TQ rating is the same. Which would you take? Would you flip a coin since they should all do about the same?

I have driven High TQ , Low HP engines and vice versa. I completely understand how a high TQ engine just feels more powerful and is fun to drive, I ALSO understand how it runs out of steam when you have exceeded the HP it has available. You can also increase TQ at the wheels simply through gearing. You can't increase HP.

You are dead set on believing what you want to believe as dead wrong as it may be. The good thing is most modern diesels have plenty of HP DUE to their high torque abilities.

Of course it works that way. Look at the Cummins engine family.

Pre 07 EPA they offered the ISB in a 300HP/600lb/ft configuration and the ISC in a 300HP/950lb/ft configuration.

The ISC had more available torque through a wider part of the powerband than the ISB had at it's peak, even though they were the same peak HP.

Like I said - where it makes its power is as important as how much peak power it makes. More available torque usually means much more broad torque curve.

In your Cat example, how they got more HP without raising the torque is simple - they spun it faster.

Remember, HP is determined by torque, not the other way around. ((TorquexSpeed)/5252)

Having said all of this, sure, if we all only ever drove at peak HP then sure, it wouldn't be a big deal, but we don't - we drive through a wide variety of conditions and RPM ranges, so in the real world I'm looking for more torque - the HP part will take care of itself.

[st687]

Get a coach with a Cummins ISX 600, there is no substitute for cubic inch.

[Daveinet]

Not so sure that is the ticket. The idea behind any pressurised intake is so that you can reduce pumping losses by using a small engine, but still get a lot of power from the boost. Right now the hot ticket is an electric motor driven turbo. Its a hybrid in that you store some energy electrical that is used to supliment the turbo. This reduces exhaust load and at the same time gets rid of turbo lag. I'd like to see it go one step farther and actually store pressurised air.

[OhhWell]

Daveinet wrote:

OhhWell wrote:
That's do-able. I can live with 45mph on a 6-7. I didn't have any trouble keeping my 60 mph cruising speed on 4%. Well, the engine was roaring but I kinda like the sound.

If you like the sound, come ride with me up a 6% grade @ 80 mph towing my Jeep :B

BTW: When one compares 2 different engines with the same HP and different torques, there is an assumption that both units are optimally geared for the desired speed. If not then all bets are off.

Also something else to keep in mind, as one hits high altitudes, a turbo is able to compensate for the lack of air density by just cramming more air in. If not for the turbo, a diesel would be much worse than gas at high altitudes. I'm waiting for a large format turbocharged gas truck engine. Gas engines run hot, so that is the real difficulty running a turbo on a heavy duty gas engine.

Yeah, I think that a small clutch activated supercharger would be perfect on a gas powered HD vehicle; one with just enough boost to compensate for the thin air.

[Daveinet]

OhhWell wrote:
That's do-able. I can live with 45mph on a 6-7. I didn't have any trouble keeping my 60 mph cruising speed on 4%. Well, the engine was roaring but I kinda like the sound.

If you like the sound, come ride with me up a 6% grade @ 80 mph towing my Jeep :B

BTW: When one compares 2 different engines with the same HP and different torques, there is an assumption that both units are optimally geared for the desired speed. If not then all bets are off.

Also something else to keep in mind, as one hits high altitudes, a turbo is able to compensate for the lack of air density by just cramming more air in. If not for the turbo, a diesel would be much worse than gas at high altitudes. I'm waiting for a large format turbocharged gas truck engine. Gas engines run hot, so that is the real difficulty running a turbo on a heavy duty gas engine.

[OhhWell]

LVJ58 wrote:

OhhWell wrote:

LVJ58 wrote:
When we bought our current class A coach our prime concern was a comfortable livable floor plan that would suit our needs as it would be our home away from home.

We really weren't overly concerned with whether it was diesel or gas powered as we would be spending more time living in it than driving it.

Over the 14 years we've had it, haven't been disappointed as it has served our needs well.

Granted, we don't go blazing up those 7+% mountain grades, but it always gets us where we're going.

I do most of my own routine maintenance, i.e., oil/filter change, lube etc. at a cost under $50.00

Bottom line, get whatever type coach that you'll be comfortable with and enjoy it.

Best of luck and safe travels....:)

Out of curiosity, what speed does your coach take a 6-7% grade at? Ours should be pretty similar power to weight.

The best I can recall I think around 45mph or so usually in 2nd gear have been on some grades not sure of the grade % and have had to drop down to 1st, but still maintain the 45mph.

Fortunately the amount of time spent navigating grades is far less than traveling on more level terrain, so I don't consider the slower speed navigating grades that big of a deal.

That's do-able. I can live with 45mph on a 6-7. I didn't have any trouble keeping my 60 mph cruising speed on 4%. Well, the engine was roaring but I kinda like the sound.

[LVJ58]

OhhWell wrote:

LVJ58 wrote:
When we bought our current class A coach our prime concern was a comfortable livable floor plan that would suit our needs as it would be our home away from home.

We really weren't overly concerned with whether it was diesel or gas powered as we would be spending more time living in it than driving it.

Over the 14 years we've had it, haven't been disappointed as it has served our needs well.

Granted, we don't go blazing up those 7+% mountain grades, but it always gets us where we're going.

I do most of my own routine maintenance, i.e., oil/filter change, lube etc. at a cost under $50.00

Bottom line, get whatever type coach that you'll be comfortable with and enjoy it.

Best of luck and safe travels....:)

Out of curiosity, what speed does your coach take a 6-7% grade at? Ours should be pretty similar power to weight.

The best I can recall I think around 45mph or so usually in 2nd gear have been on some grades not sure of the grade % and have had to drop down to 1st, but still maintain the 45mph.

Fortunately the amount of time spent navigating grades is far less than traveling on more level terrain, so I don't consider the slower speed navigating grades that big of a deal.

[OhhWell]

dubdub07 wrote:

Daveinet wrote:

Bruce Brown wrote:


Do you want a 300HP/600#/ft diesel or do you want a 300/950#/ft diesel?

Me? Ignorant as I may be I'm skipping the HP number and going for more torque.

Your conclusion is a little misleading, as both HP numbers are the same. Of course if the HP is the same, the higher torque is more desirable. But the OP's question was about the speed an RV will go up a given hill. The torque rating has ZERO to do with the answer to that question. This is absolute indisputable fact.

Know what else is indisputable? My co-worker bought a new version of my DP with the new ISL. I have the ISC. His is 380/1150 and mine is 380/1050. His goes up the passes faster than mine. This would indicate that torque indeed is a factor and that ZERO to do with the OP is actually....disputable.

dub

Right, nothing else could be at play like power curves, gearing, weights, acceleration, tires, driver, age of drivetrain? Naw, you proved it. HP as a universally established standard of quantifying the RATE OF WORK is useless and torque is all that matters. I will send your perfect scientific evidence to caterpillar and they can stop ranking their powerplants based on Horsepower.

[OhhWell]

Bruce Brown wrote:

OhhWell wrote:

Bruce Brown wrote:

Daveinet wrote:

Bruce Brown wrote:
Not the Grape Vine, but Rt 26 out of Johnson City, Tn;
2000 V10 gasser MH - brought to it's knees, 30 MPH tops
2003 DP w/ Cat 3126, 330HP/860 TQ - 55 MPH
...
If you're ready for a DP skip the HP number and look at the torque.

I'd like to see you reconcile your statements with the post from Greyhost above. My guess is you have not considered the weight of either coach, or the altitude. An old V10 has serious breathing problems, which will be exacerbated by any kind of altitude. No doubt that is a big factor, so you argument of torque doesn't hold water. (never mind that it defies physics)

I have no idea why he was limited to 50 MPH in his diesel - ours does not.

As to the rest, I'm offering real world expirence, not a physiscs class. If it makes you feel better to say I'm wrong then OK, make yourself happy.

If you want to buy a low torque engine go ahead, I won't.

We've owned gassers and diesels in both our MH's and pickups. Gas has it's place, but when it comes to hard work I'll take a diesel every time, and the bigger the better.

Nothing wrong with loving a high torque engine as they make for a very pleasant driving experience. When you say ignorant things like ignore the HP number, it's all about torque; unfortunately, you are doing a disservice in addition to being just plain wrong.

Ask yourself;

Do you want a 300HP/600#/ft diesel or do you want a 300/950#/ft diesel?

Me? Ignorant as I may be I'm skipping the HP number and going for more torque.

Take a look at the torque curves and you'll know why. :W Where an engine makes power is just as important as how much it makes. A low torque diesel just can't offer what a high torque one can. And until you've owned both (we have) you just won't understand.

You gotta be kidding me right? You expect anyone with a good sense of reasoning to take you seriously after that?

besides, it doesn't usually work out like that. Lets take the Cat 3126 that is offered in different power levels from 300 to I think 350 HP but the TQ rating is the same. Which would you take? Would you flip a coin since they should all do about the same?

I have driven High TQ , Low HP engines and vice versa. I completely understand how a high TQ engine just feels more powerful and is fun to drive, I ALSO understand how it runs out of steam when you have exceeded the HP it has available. You can also increase TQ at the wheels simply through gearing. You can't increase HP.

You are dead set on believing what you want to believe as dead wrong as it may be. The good thing is most modern diesels have plenty of HP DUE to their high torque abilities.

[dubdub07]

TucsonJim wrote:

dubdub07 wrote:

Daveinet wrote:

Bruce Brown wrote:


Do you want a 300HP/600#/ft diesel or do you want a 300/950#/ft diesel?

Me? Ignorant as I may be I'm skipping the HP number and going for more torque.

Your conclusion is a little misleading, as both HP numbers are the same. Of course if the HP is the same, the higher torque is more desirable. But the OP's question was about the speed an RV will go up a given hill. The torque rating has ZERO to do with the answer to that question. This is absolute indisputable fact.

Know what else is indisputable? My co-worker bought a new version of my DP with the new ISL. I have the ISC. His is 380/1150 and mine is 380/1050. His goes up the passes faster than mine. This would indicate that torque indeed is a factor and that ZERO to do with the OP is actually....disputable.

dub

It would be interesting to note the weight difference between the two units.

If there is, the new one is heavier. ISL 9 weighs more than an ISC 8.3.