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Old 09-06-2020, 08:46 AM   #29
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Originally Posted by shootist View Post
The isx is a real truck engine, much,more torque, comes with the allison 4000 trans. Weighs 3000 pounds verses the 1600 or so of the isl,ism . mileage isn't any different that I have seen between my 400 isl and my friends 525 isx. About 7. I would not go above 550 hp as the valve problem is well known in the bigger hp motors.
My “new” 08 Navigator ISX 525 (not exempt from #6 problems) just turned up 62K miles (20K of mine) and the engine computer says it’s used 10K gallons...6.2 mpg. My 04 Dynasty ISL 400 did the same at 70K miles...7.0 mpg while pushing 4,000 less lbs. While I was happy with the performance of the ISL (didn’t know better) NO WAY would I go back to a ISL in a big MH. On a Interstate I can now pull out into a small gap and quickly pass the slower vehicles. Before I needed a 2 football gap to not upset those in the passing lane. With the ISL on a straight 2 lane, if I could see a oncoming vehicle, I couldn’t pass, now I can. At 7K miles/year the extra 100+ hp, 3’, and 4K lbs is costing me a extra 166 gallons or $350... worth it for me.
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Old 09-06-2020, 09:10 AM   #30
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While I was happy with the performance of the ISL (didn’t know better) NO WAY would I go back to a ISL in a big MH. On a Interstate I can now pull out into a small gap and quickly pass the slower vehicles. Before I needed a 2 football gap to not upset those in the passing lane. With the ISL on a straight 2 lane, if I could see a oncoming vehicle, I couldn’t pass, now I can.
I totally agree with your observations. But what most people don't understand is that what you are commenting on has very little to do with the large engine's horsepower and a huge amount to do with its torque.

Torque is an often difficult to understand concept, but, in the case you are describing it manifests itself in the ability of the engine to change the speed of the vehicle quickly. If you've ever been stuck behind a slow truck on an uphill grade and wanted to pass him you'll appreciate having the huge torque of a big block diesel.

Torque is pretty much a function of engine displacement in diesels. My C-12 has 1550 ft-lbs of torque compared to the ~800 of the popular Cummins ISB engine. It does make a difference.

IMO that's a big advantage of buying an older DP; they used to build many of them with large block engines. These days most of the big diesels are limited to MH's costing very big bucks!
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Old 09-06-2020, 02:36 PM   #31
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X2 on the above^^^ and 1650ft lbs is a big increase over 1200 ft lbs. I’ve posted many times that you need to look at the torque of a MH engine, not the HP, especially the Cummins ISB, ISC and ISL. You can have a 350 HP ISB with only 880 torque or a 340 ISC with 1100. BUT, there’s very little difference in the torque of a 400, 425, or 450 ISL...it’s more a year/ amount of pollution distinction as the torque is 1200 to 1250 because of the Allison 3000 tranny is maxed out at 1250 ft lbs.
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Old 09-06-2020, 03:26 PM   #32
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Power to weight ratio is an important consideration when shopping for a coach.

During the manufacturing era in which the OP is currently shopping, there was more of a tendency for coach builders to equip their product with adequate power, compared to power trains installed after 2009-10.

I don’t know how many +40’ tag-axle coaches were equipped with a 350/1050/3000 power train. It would seem like a poor choice. Similarly, a ~500/~1550/4000 power train in a sub-40’ coach with a GVWR in the mid-30K range would seem like an equally poor choice.

The right tool for the job usually gets it done.
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Old 09-06-2020, 03:36 PM   #33
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Similarly, a ~500/~1550/4000 power train in a sub-40’ coach with a GVWR in the mid-30K range would seem like an equally poor choice.
I'm not sure why you consider this to be a poor choice. My 2000 Beaver Patriot Thunder has a 425 HP, 1550 ft-lb engine in a 34,000 lb coach and it is a dream to drive. Is it over-powered? Sure, but that doesn't make it a poor choice. I get ~8 mpg and can move out from a stop more like a car than a MH.
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Old 09-06-2020, 04:26 PM   #34
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You guys are definitely giving me "Torque Envy"

Our 2001 Alpine has the ISC350/1050/3000 combo and while I can typically do better on hills than the trucks I would love to have another 500Lbs of torque....now that would be awesome!!!
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Old 09-06-2020, 05:19 PM   #35
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I'm not sure why you consider this to be a poor choice. My 2000 Beaver Patriot Thunder has a 425 HP, 1550 ft-lb engine in a 34,000 lb coach and it is a dream to drive. Is it over-powered? Sure, but that doesn't make it a poor choice. I get ~8 mpg and can move out from a stop more like a car than a MH.
Remarkably, at 40’, your coach is a length I specifically did not mention. A 40’ will tend to be heavier than a sub-40’ coach. A longer, heavier chassis, an additional storage bay, more cabinets, counters, tile floors, maybe an addition slide or two. It is a length that leads to a decision of a power train choice, that more often than not gets the short straw. Beaver, Country Coach, Alpine and Monaco generally opted for more power.

Using your coach as an example, there is additional weight to factor in with a larger engine, transmission and other assorted components necessary to make everything work. More weight needs more power, so at some point it becomes a tail chasing exercise. More weight eats into CCC, compared to the same coach with a lighter power train. Or, you start adding more heavy components to add more CCC and now more power is needed. There’s also a cost factor for the manufacturer to consider.

Using my 37’ coach as an example, it rolled out of the factory at ~26.5K. Fully loaded we’re under 31K. The 400/1200/3000 drive train is quite peppy, even with a 5K toad. It is more than adequate. Trying to stuff a C-12 or ISM and an Allison 4000 into the package would have been a complete waste of time and money. AKA: a poor choice for a sub-40’ coach.

Make sense?
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Old 09-06-2020, 05:32 PM   #36
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5 years ago I paid 80K for an '04 MADP, 400 ISL Cummins 2 slides. With 80K miles. If I Junk it when I'm done with it I'll be over 200K ahead of the guy that bought it new. I have put 8K into it plus routine maintenance.
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Old 09-06-2020, 06:50 PM   #37
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Remarkably, at 40’, your coach is a length I specifically did not mention. A 40’ will tend to be heavier than a sub-40’ coach. A longer, heavier chassis, an additional storage bay, more cabinets, counters, tile floors, maybe an addition slide or two. It is a length that leads to a decision of a power train choice, that more often than not gets the short straw. Beaver, Country Coach, Alpine and Monaco generally opted for more power.

Using your coach as an example, there is additional weight to factor in with a larger engine, transmission and other assorted components necessary to make everything work. More weight needs more power, so at some point it becomes a tail chasing exercise. More weight eats into CCC, compared to the same coach with a lighter power train. Or, you start adding more heavy components to add more CCC and now more power is needed. There’s also a cost factor for the manufacturer to consider.

Using my 37’ coach as an example, it rolled out of the factory at ~26.5K. Fully loaded we’re under 31K. The 400/1200/3000 drive train is quite peppy, even with a 5K toad. It is more than adequate. Trying to stuff a C-12 or ISM and an Allison 4000 into the package would have been a complete waste of time and money. AKA: a poor choice for a sub-40’ coach.

Make sense?
i totally agree but.....it would be bad ass🤣🤣
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Old 09-06-2020, 06:57 PM   #38
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I'm not sure why you consider this to be a poor choice. My 2000 Beaver Patriot Thunder has a 425 HP, 1550 ft-lb engine in a 34,000 lb coach and it is a dream to drive. Is it over-powered? Sure, but that doesn't make it a poor choice. I get ~8 mpg and can move out from a stop more like a car than a MH.
"Too much power is just right" and "there is no replacement for displacement" - Carrol Shelby
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Old 09-06-2020, 07:18 PM   #39
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"Too much power is just right" and "there is no replacement for displacement" - Carrol Shelby
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Old 09-07-2020, 04:34 AM   #40
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Power to weight ratio...

Usually you will find most manufacturers specking out coaches at around 1 HP per 100 pounds of coach. That is a general rule of thumb.

My father owned an 05 American Eagle with a 500 HP Cummins. That coach's GVWR was rated around 44K pounds. 88 pounds per HP. That combination was an effortless drive on any road or any grade. My 2006 450 Lxi is a 52K pound bus with a C13 525 HP. 99 pounds per HP. If I want a similar HP to weight ratios as Pop's Eagle I can upgrade the C13 to 600 HP. That is 87 pounds per HP.

Also true as stated there is no replacement for displacement. Big blocks produce big flat torque curves. Really needed in heavier coaches.
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Old 09-07-2020, 07:33 AM   #41
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I totally agree with your observations. But what most people don't understand is that what you are commenting on has very little to do with the large engine's horsepower and a huge amount to do with its torque.

Torque is an often difficult to understand concept, but, in the case you are describing it manifests itself in the ability of the engine to change the speed of the vehicle quickly. If you've ever been stuck behind a slow truck on an uphill grade and wanted to pass him you'll appreciate having the huge torque of a big block diesel.

Torque is pretty much a function of engine displacement in diesels. My C-12 has 1550 ft-lbs of torque compared to the ~800 of the popular Cummins ISB engine. It does make a difference.

IMO that's a big advantage of buying an older DP; they used to build many of them with large block engines. These days most of the big diesels are limited to MH's costing very big bucks!
Right on about torque! Our previous motor home with a cummins and about 800 torque would just craw up long grades. Our current coach with a C12 glides over many long grades often without shifting down when cruising. Love it!
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Old 09-07-2020, 08:45 AM   #42
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Jzack’s dates are correct, late 02 for EGR, 07 DPF (except for MaxForce) & 2010 DPF plus DEF. Yes a lot of Monaco 07-08 rigs have a 06 engine...EGR only like my 08 Navigator.

https://www.cummins.com/engines/isl-epa-2004. Cummins would disagree, at least on the isl. I didn't check others.
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