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Old 08-28-2019, 12:54 AM   #1
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340 HP versus 360 & 400 HP versus 450 HP

I just sold a 40 foot Ventana LE with a 360 HP Engine. I am buying a 44 foot Ventana with a 400 HP. I have been constantly told the big difference is torque and that gives you the additional power to climb hills and faster starts to pull on the highway. If this is true - what is the advantage of 450 over 400 and 360 over 340? The 360 on the 40 footer was terrible at taking off - was scary getting onto highways. I owned a 450 before and that coach would really climb mountains and enter the highways. It was on a Spartan 40 foot chassis. The new coach, which hasn't arrived yet, will be on a Freightliner and has a tag axle. I drove a 44 foot coach with a 400 and it moved well while doing the demo ride. But it was unloaded and not towing anything. So, this really got me to thinking - is the extra horsepower available really doing much? I understand it is the same engine with an internal electronic chip (?) that has something to do with the increased horsepower - but if the torque remains the same - is the additional HP really doing anything or is it bragging rights? Also, does the the additional HP affect mileage?
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Old 08-28-2019, 07:13 AM   #2
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I dont know the difference between each power level in the 6.7 or the 8.9 but we went from 6.7 340hp to 8.9 380hp and it was a world of difference. Basically in the same size coaches.
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Old 08-28-2019, 07:36 AM   #3
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I owned a 1993 diesel pusher and under powered !
I since talked to many DP owners and their rule of thumb is that the HP of a coach should go with the gross weigth of the coach:
- a 40,000 lbs should have at least 400 HP
- over that weight, it should have at least have 450 HP
and I find it funny that it matches the length of the coaches also:
- a 40 footer should have 400 HP and more
- a 45 footer should have 450 HP and more...
p.s. just numbers
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Old 08-29-2019, 10:02 AM   #4
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Good chance you'll find the power to weight ratio of the old and new coaches to be similar. Meaning you will not feel much difference in acceleration or hill climbing.

Usually when you climb the pecking order of the manufacturers, along with more goodies and luxuries and complexities of the coaches themselves, you also improve your power to weight ratio's by getting larger engines too. say 600-650HP, and yes more torque too 1500 to the 1900 range, depending upon specific engine. With this higher HP/Torque, you would feel better acceleration, hill climbing and just as important - Braking HP from larger displacement engines.

Regardless of the engine in a coach, driver's active involvement in keeping the RPM's in the sweet spot by manually shifting. (We humans can see, and proactively shift and be prepared for a hill. Our Engine and Trans ECM's can't see, and thus are reactive in their shifting. And on an engine with marginal power to weight ratio's, once you drop speed/RPM's - it's very hard to recover while say climbing a hill...

I know two people who have bought RV's I'm the past 6 months. Both went for older higher end, towards the top of the manufacture's food chain models - to get the better suspensions, and larger engines. They 'Dropped years to remain within budget range, and bought the highest quality coach that met their needs.'. And both of them saved some funds, to put into customizing the coaches to their personal likes. By buying a bit older coaches, they spent the same funds as they would have to buy a mid tier/model new, and are very happy with their choices.

Not trying to hijack or shift the focus of your thread, but was sharing how these two gents went about their new to them coach purchases. And I'll share, I have another couple I know that bought a retirement coach two years ago. The DW wanted to buy new, so they could set it up from the manufacturer they way the wanted it. Budget wise they bought mid tier model, and have no regrets at all.

I always kid, if it were not for the mix of 'Buy New' vs 'Buy Used' - no 'Used' would be available! So it's a Win/Win!

Enjoy your new coach, travel safe,
Smitty
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Old 08-29-2019, 10:19 AM   #5
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Yes same peak torque in a ISL 400 hp versus 450 hp, however the peak torque extends into the upper rpm range as I understand it, for the higher horsepower engine. Horsepower is a calculated number based upon torque and rpm. So, yes the extra horsepower is real, not just a bragging thing. You would need to floor it, so that the rpms would get into a higher range before the transmission shifts to feel it.
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Old 08-29-2019, 01:46 PM   #6
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An ISL 450, will not accelerate or climb as fast as say an ISM 450.

Newmar did put the ISM 450 into their mid tier model, vs the next level up got the ISM 500. And again, higher up the Newmar food chain, the ISX is available in different HP ratings and displacements, depending upon specific model and year.

While 450 is 450, as noted by pasdad1, how and where the HP (And Torque) are available in the RPM curve - will make a big difference in usability!

Travel safe, have fun,
Smitty
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Old 08-29-2019, 06:22 PM   #7
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The little Cummins ISB (both 5.9 and 6.7L) is not a good fit for a 40' coach, especially if towing. It's a great engine and I've had several in Dodge pickups and even in Case tractors and backhoes, but just not enough torque for a 40' coach.
The Cummins ISL is a much better choice whether its the 400, 425, or 450hp version the torque is 1250 ft lbs.

If you drop back a few years, you can find coaches with the Cummins 10.9L ISM in 450 and 500hp versions. These are absolutely great motor home engines. They weigh 1000 lbs less than the big ISX and they produce great power. They are usually rated at 1550 ft lbs and are actually fun to drive and do a great job towing.

Always ask the engine torque rating and if it's less than 1000 ft lbs, walk away.
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