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Old 02-19-2016, 10:12 PM   #1
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Cummins 5.0-liter V8 in compact DP

According to MotorHome Magazine, Tiffin is the first company to use the relatively new, small, and lightweight Cummins ISV 5.0-liter V8 diesel in a DP. I'm not in market for a Diesel Pusher, but certainly hope this is part of a broader industry trend towards offering smaller motorhomes.

In a way it seems odd to see a relatively compact and narrow DP about the same width as an Axis/Vegas when for years the trend was towards making motorhomes larger. Even the specified interior headroom at only 78-inches is a throwback. That's not to say downsizing hasn't been tried before, because I recall tiny DPs in the past. They just didn't succeed for long.

What do you think? Innovation or a mistake? And will it spread to other segments?

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Old 02-19-2016, 10:52 PM   #2
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Traded in my 39 ft DP for 25.3 Axis but that's just me and my wife. Looked at the MB version but the chassis costs a premium and my Ford V10 (E450) is serviceable at my dealer we have used for years.
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Old 02-20-2016, 12:37 AM   #3
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I had looked at some MB versions in the same size category as the Vegas 24.1 that I bought. The MBs were all about $20,000 more than the Vegas and did not have nearly the storage or fresh, black, and gray water capacities. I'm very happy with our Vegas. Perfect size for my wife & I (both retired) and we love the twin beds in the 24.1 floorplan.
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Old 02-20-2016, 02:14 AM   #4
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I would think Nissan would be able to service that motor, as it is the same going into their pick ups
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Old 02-20-2016, 02:23 AM   #5
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Originally Posted by Baddad53 View Post
Traded in my 39 ft DP for 25.3 Axis but that's just me and my wife. Looked at the MB version but the chassis costs a premium and my Ford V10 (E450) is serviceable at my dealer we have used for years.
Had your diesel pusher been much smaller (like an Axis in width and height but about 33-feet long), would it have made a difference in wanting to trade?



It will be interesting to see if fuel efficiency for this 23,500-pound GVWR DP is significantly better than other/larger DPs, and also if much better than an Axis/Vegas-size gasoline motorhome. Cummins previously predicted 20 to 40 percent better fuel economy out of this 275 HP 5.0L diesel V8 compared to a Ford gasoline V10, but I'm sure that was based on similar size and weight.
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Old 02-20-2016, 04:46 AM   #6
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Originally Posted by Chance View Post
Had your diesel pusher been much smaller (like an Axis in width and height but about 33-feet long), would it have made a difference in wanting to trade?



It will be interesting to see if fuel efficiency for this 23,500-pound GVWR DP is significantly better than other/larger DPs, and also if much better than an Axis/Vegas-size gasoline motorhome. Cummins previously predicted 20 to 40 percent better fuel economy out of this 275 HP 5.0L diesel V8 compared to a Ford gasoline V10, but I'm sure that was based on similar size and weight.
I got 7 to 8 mpg with DP - I am getting 8 to 10 mpg with V10.
My wife hated the size while traveling and liked it when it was parked. Only thing we gave up was washer/dryer. Plus she is driving it to releave me on trips ...she would never do that in the DP. Yes it was about size and costs. But my wife and I thought that the Axis/Vegas was just the right size (tanks and living space for us) MB based B's and C's. The ones with room we wanted had no capacity for GVWR.
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Old 02-20-2016, 02:23 PM   #7
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Originally Posted by Baddad53 View Post
I got 7 to 8 mpg with DP - I am getting 8 to 10 mpg with V10.
My wife hated the size while traveling and liked it when it was parked. Only thing we gave up was washer/dryer. Plus she is driving it to releave me on trips ...she would never do that in the DP. Yes it was about size and costs. But my wife and I thought that the Axis/Vegas was just the right size (tanks and living space for us) MB based B's and C's. The ones with room we wanted had no capacity for GVWR.
That's quite an improvement.

If Cummins is correct about their 20 to 40 percent improvement over a V10, it would suggest your 8 to 10 MPG could become 10 to 14 MPG if an Axis-size motorhome had a 5.0L diesel V8. And that sounds realistic compared to Winnebago Class A on Sprinter chassis that reportedly get as high as 17 MPG (granted they are slightly smaller and lighter than Axis).

What I don't get about diesels is buyers' acceptance of low power-to-weight ratio compared to many gas motorhomes. For example, this new Tiffin with 275 HP for 23,500-pound GVWR would be the same as Ford installing a 3.2L 185 HP inline-5 in an Axis. That would also make an Axis close in power to a 3.0L Sprinter V6. Would that seem adequate after driving a 305 HP V10?



By the way, I agree the larger Mercedes Class A on Sprinter chassis is a little low on GVWR for the way it's built. I also don't like the narrow rear track for such a tall motorhome, or the limited places to get it repaired. We do like the overall size and build quality which appear very good; although higher quality should be expected at that price.
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Old 02-20-2016, 03:02 PM   #8
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The problem I have with the Tiffin concept is the coach riding on "Tiffin's proprietary PowerGlide chassis". Who can repair that chassis when there is a problem and what is the chassis warranty? My nearest Tiffin dealer has a reputation for being great on sales and lousy on service. They are also a Thor dealer.

You can talk all you want about HP to weight ration but unless you know the specs of the entire power train you don't have any idea what the performance will be. What is the transmission gearing, what is the gear ratio of the rear end? Yes you may have an increase in "engine" performance over gas but what is the overall performance of the power train and chassis combined?
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