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Topic: Fuel economy difference between 350hp and 450hp Cummins? (Read 2878 times) previous topic - next topic

Fuel economy difference between 350hp and 450hp Cummins?

Curious to the difference in fuel economy between a 350hp and the 450hp.  I know there are a lot of factors.  Hoping to hear from someone who has owned both so driving habits would be the same.
Jerry
Jerry & Nanci
1999 U270 34'WTFI
2011 Malibu
A smart man knows what to say, a wise man knows when to say it.

Re: Fuel economy difference between 350hp and 450hp Cummins?

Reply #1 –
About 1 mpg difference, but also much heavier, probably nearly 9,000 pounds more
previous 1984 35 ft ORED 250 HP 3208 Cat       
previous 1998 40 ft U295 CAI 325 hp Cummins
previous 2003 40 Ft u320 build #6140 450 Cummins M11.                                                         
1999 Mazda Miata
Ron, Nancy, Tipper the cat, Max The dog
1997 U 270 36 ft build number 5174 8.3 Cummins

Re: Fuel economy difference between 350hp and 450hp Cummins?

Reply #2 –
Fuel burn is controlled by your right foot.  When I upgraded my ISM450 to the ISM500, I strongly believe with the resonator change also, the fuel mileage improved. Over known distances I consume the same amount of fuel, but arrive quicker, so if I drove the exact same, no doubt the mileage would be better.
That is my story and I'm sticking with it. ;D

Re: Fuel economy difference between 350hp and 450hp Cummins?

Reply #3 –
I am also about one mpg different but my old coach was 34 and this one is 42 foot.  The grand Cherokee cost me a half a mile per Fallon over the wrangler too. 
2025 Wanderbox Outpost 32 on F600 Expedition Motorhome
2015 Born Free Royal Splendor on Ford 550 nonslide version  for sale
Former Coaches  covering. 360,000 miles
1999 34 U270
2000 36 U320
2001 42' double slide U320
2018 Jeep Rubicon

Re: Fuel economy difference between 350hp and 450hp Cummins?

Reply #4 –
My VMSpc reports our ISM 11 450hp, 2001 U320, 36' FT has gotten 8.0 mpg over 65K miles (since the beginning of engine time).  Three drivers, two different tows, flat lands, mountains, back roads, slow roads, hilly roads, lots of small town roads, everywhere.  Same coach as Dave M but without the hot rod mods (yet)

A light load, no tow 63 mph drive from CA to MN probably with a tail wind got us 9.4 mpg over 2400 miles.

I like the additional power towing especially out West.  For our 8,000 miles or so per year the difference between 9 and 8 mpg is just over 100 gallons per year or about $400.

Roger
Roger Engdahl and Susan Green
2001 U320 3610 #5879 (Home2) - 2014 Jeep Cherokee or 2018 F150
Hastings, MN

Re: Fuel economy difference between 350hp and 450hp Cummins?

Reply #5 –
We're seeing 8.4mpg over 131,000 miles and 4 owners on our 40 ft 1999 M11 towing

best, paul
1999 U320 40' 1200 watts on roof. 12cf AC/DC Cold plate fridge/freezer. VMS 240 CL Honda Element

Re: Fuel economy difference between 350hp and 450hp Cummins?

Reply #6 –
Sounds like not a whole lot of difference then, unless you start towing heavy.
My 280 with turned up 8.3 got around 9.3 going to New Mexico and back. Doubt we can pull quite as much as a big 320.
Tom
1998 U320 40'

Re: Fuel economy difference between 350hp and 450hp Cummins?

Reply #7 –
Our 1990 U280 with Cat 3208T gets between 9.3 and 10 mpg at 75 mph on the interstate.
It's only 250hp.  That said, it accelerates faster than our "new" U320 400hp M11 - I'm checking to see if it has a hole in the tank--- it gets about 7mpg.  Our Toad is a 2000 Jeep Wrangler.
Current coach 1996 U320 40'
Previous coach, 1990 36' U280

Re: Fuel economy difference between 350hp and 450hp Cummins?

Reply #8 –
Quote from: Kemahjohn –
Our 1990 U280 with Cat 3208T gets between 9.3 and 10 mpg at 75 mph on the interstate.
It's only 250hp.  That said, it accelerates faster than our "new" U320 400hp M11 - I'm checking to see if it has a hole in the tank--- it gets about 7mpg.  Our Toad is a 2000 Jeep Wrangler.
      Weight matters! We almost never see 75mph, 65 is normal cruise speed for us.
Tom
1998 U320 40'

Re: Fuel economy difference between 350hp and 450hp Cummins?

Reply #9 –
When I started towing,  my fuel economy improved about 1mpg. 

My towed is somewhat heavy,  but my speed slowed from 65 to 60.
Tom Lang K6PG (originally  KC6UEC)
and Diane Lang
2003 38 U295 build 6209
2016 Jeep Grand Cherokee Summit Ecodiesel
still have tow-ready 2006 Acura MDX 
Temple City, California
Motorcade 16681 California Chapter President
SKP 16663 member of SKP Park of the Sierra, Coarsegold California
FMCA F071251
Retired electrical and electronic engineer

Re: Fuel economy difference between 350hp and 450hp Cummins?

Reply #10 –
My ISC gets 8 MPG average pulling a 4dr Wrangler at 65-68 MPH. Curious to see what happends now that we are live aboard and a good bit heavier. 
Bruce, Linda, and Macy
Zoey RIP 1/20/19
1999 U295 40' build #5400
2017 silver Jeep Wrangler, 1260 watts of solar on top
Moving around the country