Diesel Power

[canes1]

We are thinking about upgrading from our 2004 Damon DP with a 400 ISL Cummins to possibly a 2012 or newer coach with a tag axel. We wanted to know when the emission changes happened and how much the emission reduces the output of power. Should we make the change now or hold off for a couple more years as our rig is powerful enough to make it over the toughest grades. Any thoughts?

[Steve Ownby]

Originally Posted by canes1

We are thinking about upgrading from our 2004 Damon DP with a 400 ISL Cummins to possibly a 2012 or newer coach with a tag axel. We wanted to know when the emission changes happened and how much the emission reduces the output of power. Should we make the change now or hold off for a couple more years as our rig is powerful enough to make it over the toughest grades. Any thoughts?

Engines build after:

1/1/2007 require diesel particulate filter and fuel is changed to ULSD.
1/1/2010 require a reduction of NOX which all but Navistar accomplish with Diesel Exhaust Fluid (DEF).

Due to heavy buying of engines most coach builders did not reflect these changes for one model year. Engines produced after 1/1/10 generally are rated at a higher horse power than previous engines. This is due to a portion of emissions reduction being moved out of the engine by using the DEF. Engine manufacturers were able to de tune the EGR system somewhat which gave a higher horse power.


Steve Ownby
Full time since '07

[canes1]

Thanks Steve, so...
When purchasing do we want to make sure that DEF is part of the equation? Is that something that will boost the torque as well? Sorry for the lack of knowledge of diesel performance. We encounter a lot of steep grades when travelling and we just want to make sure that newer diesels have plenty of torque to get us over without overheating or begging to get to the top.

[dvmweb]

DEF is a good thing overall. As stated in previous threads, Euopeans have been doing it for a long time. It is only a little bit more fuss, and really helps clean up the exhaust. Make sure the ecm is upgraded and the DEF system is up to date. Our pump failed, it leaked, and was a known problem, for instance.


2013 FleetWood Expedition 38B

[Steve Ownby]

Originally Posted by canes1

Thanks Steve, so...
When purchasing do we want to make sure that DEF is part of the equation? Is that something that will boost the torque as well? Sorry for the lack of knowledge of diesel performance. We encounter a lot of steep grades when travelling and we just want to make sure that newer diesels have plenty of torque to get us over without overheating or begging to get to the top.

When facing a 6-7-8% grade in the DP there is no such thing as enough power. The ISL is up to 450 hp and about 1250 pounds/ft of torque. The performance of the ISL 450 will be about what you are use to. The big thing that will affect performance with be the weight of a new coach.

The biggest thing you can do in climbing long grades is, keep your RPMs up around 2000 or certainly within a couple of hundred RPMs of your governed max. It's not true that torque gets you up the hill, it's horse power. Torque can be multiplied by the transmission but horse power is not. The high RPMs will help keep your heat under control also.


Steve Ownby
Full time since '07

[Ray,IN]

From listening to owners of MH's newer than 2012, they say mileage has improved a bit over previous model years, which somewhat offsets the expense of DEF.
The main complaint I hear is about coach mfgrs putting the DEF fill on the passenger-side of the coach, which is a complication when filling at truck stops.

[CampingCajun]

The use of DEF allows engine builders to adjust timing for a more efficient burn. The DEF cools exhaust temperatures allowing them to get a little more fuel mileage out of them.

[Moxy]

Originally Posted by Steve Ownby

When facing a 6-7-8% grade in the DP there is no such thing as enough power. The ISL is up to 450 hp and about 1250 pounds/ft of torque. The performance of the ISL 450 will be about what you are use to. The big thing that will affect performance with be the weight of a new coach.

The biggest thing you can do in climbing long grades is, keep your RPMs up around 2000 or certainly within a couple of hundred RPMs of your governed max. It's not true that torque gets you up the hill, it's horse power. Torque can be multiplied by the transmission but horse power is not. The high RPMs will help keep your heat under control also.


Steve Ownby
Full time since '07

you seem to more about this than I do Steve, so what you are saying is a 400 hp engine with say 600lbs of torque will go up the hill at the same pace as a 400 hp engine with 1250lbs of torque?

does not seem to make sense so please explain it to me would ya.

Thanks

Moxy

[Steve Ownby]

Originally Posted by Moxy

you seem to more about this than I do Steve, so what you are saying is a 400 hp engine with say 600lbs of torque will go up the hill at the same pace as a 400 hp engine with 1250lbs of torque?

does not seem to make sense so please explain it to me would ya.

Thanks

Moxy

HP and torque are both measures of the force produced by an engine. Truth be told, to have a vehicle that's easy to drive you need as much of both as possible. If the objective of climbing a grade is to keep speed up to keep with traffic then keeping the engine RPMs as close as possible to max HP RPMs is the way to do that. In the example you site, theoretically the answer is yes. In the real world it's not that easy. The engine with 1250 lbs of torque would produce its 400 HP at a much lower RPM and would have a much flatter HP curve. The 600 pound engine would require much higher RPM and would likely have a steep HP curve. Drop off that RPM just a little bit & you can't recover. The thing is HP and torque are linked by RPM. HP is actually calculated from torque which is the force that is actually measured on a chassis Dyno. The reason both HP and torque go up together is that, because torque decreases with RPM as HP increases. The big HP increases come about as engine designers flatten out the torque curve and get more torque available at higher RPMs.

I get flummoxed trying to wrap my head around the HP/torque relationship. I just try to keep in mind that I need to need my RPMs up on a long pull so I'm as close as possible to my HP peak.


Steve Ownby
Full time since '07

[slickest1]

Running high rpms works with a gas engine and higher horse power.
Lower rpms and higher torque is more common in Diesel's.
Most diesel engines the torque curve starts to drop off at 1800. Just watch your boost gauge if you have one. It will start dropping off as the engine revs higher.

[Moxy]

Originally Posted by Steve Ownby

HP and torque are both measures of the force produced by an engine. Truth be told, to have a vehicle that's easy to drive you need as much of both as possible. If the objective of climbing a grade is to keep speed up to keep with traffic then keeping the engine RPMs as close as possible to max HP RPMs is the way to do that. In the example you site, theoretically the answer is yes. In the real world it's not that easy. The engine with 1250 lbs of torque would produce its 400 HP at a much lower RPM and would have a much flatter HP curve. The 600 pound engine would require much higher RPM and would likely have a steep HP curve. Drop off that RPM just a little bit & you can't recover. The thing is HP and torque are linked by RPM. HP is actually calculated from torque which is the force that is actually measured on a chassis Dyno. The reason both HP and torque go up together is that, because torque decreases with RPM as HP increases. The big HP increases come about as engine designers flatten out the torque curve and get more torque available at higher RPMs.

I get flummoxed trying to wrap my head around the HP/torque relationship. I just try to keep in mind that I need to need my RPMs up on a long pull so I'm as close as possible to my HP peak.


Steve Ownby
Full time since '07

not to dispute because I don't know for sure but I was always under the impression I wanted to be near my max torque rpm climbing hills letting the Allison decide which gears to be in. I dunno

Moxy

[Steve Ownby]

Here is a quote I got from a Cummins seminar at an FMCA National rally:

"Cummins recommends that when pulling a grade to let the trans downshift to the appropriate gear to keep the engine within 500 RPM of it's maximum governed RPM. That will keep the engine in the power band and the RPM at a safe level to ensure proper cooling via the radiator and oil pump."

My particular engine is governed at 2100 RPM. My max HP occurs at 1700 RPM. I shoot for climbing at 1600. There is a 7% grade on I26 at the SC/NC state line. If I don't work to keep my RPMs up to that level, my engine temps climb to 200 and mph drops to 40 by the time I top the grade. If I manually shift earlier & keep my RPMs up at the 1600-1700 level my temp stabilizes at just over 190 & speed up over 45 at top.


Steve Ownby
Full time since '07

[Koop]

Okay, I sense some confusion here. Please understand that torque is measured through a dynamometer, a device that measures force. Horsepower is a derived figure, a mathematical equation of force over time. SAE horsepower is (torqueXRPM)/5252.

In the real world, torque gets you moving, horsepower gives you speed. Going uphill or dealing with any high load situation, you cannot fully load an engine at max torque RPM for a sustained period of time without consequence (i.e overheating). It's a better idea to allow the engine to rev within it's it's limitations (near peak HP) and allow adequate cooling and reduced cylinder pressures.

In other words, mashing the pedal to the floor at max torque RPM will be fatal in the long run, sacrificing fuel mileage for reasonable RPM and horsepower is much more sympathetic to your powerplant.

[DD788Snipe]

My friend that's a heavy equipment mechanic (35 years). Hates the DEF system and filters. According to him they are maintenance nightmares and they do lower your fuel mileage and power produced. With Flat Rate labor hovering around $100 and hr. that can get costly. Why do you think Caterpillar pulled out of the open road and marine market? On a Cummins engine system If you had to replace the whole exhaust system, just the parts alone are $3500 to $4000 + labor. I purposely purchased my 2006 rig two years ago because it didn't have the environmental exhaust systems on it. I don't understand the Feds. A motorhome is on the road so little compared to a transit bus or a long haul truck system. If you could break down the percentage of emissions put into the atmosphere by RV's just in North America alone I don't think it would even register .0001% on the scale. There are a lot of mid-2000 rigs out there for a lot less money and low miles that you could use that money that you would save to upgrade anything you want to and not take the hit in depreciation. Besides the DEF injection system is just a band aid and is interim till the industry can figure something more permanent out. So they will change again, that's the emissions game the EPA likes to play. As for coaches? IMHO, look at Newmar, Tiffin, Entegra or Country Coach, anyway that's my 2 cents added.