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Old 10-20-2018, 11:20 AM   #1
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Optimal speed for 400 Cat engine

Got a 40 ft Fleetwood Revolution pusher. What is the optimal speed range for best fuel mileage and engine performance?
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Old 10-20-2018, 11:31 AM   #2
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At 65 you should be in the most torque range, I run 65-70 on mine mileage stays about the same bad.
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Old 10-20-2018, 12:46 PM   #3
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This is my understanding...

Look at your engine spec, note down "Max torque xxxx lb-ft at yyyy rpm". When your engine is revving at yyyy rpm, that is the optimal speed to get your max fuel mileage.

For example, my Cummins ISC 350 has a peak torque of 1,050 lb-ft at 1,600 rpm. When I am cruising on the road, I want my engine running at 1600 rpm neighborhood. On a flat road without a strong head wind,my coach speed is about 62 mph.
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Old 10-20-2018, 12:57 PM   #4
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Really depends on the rig. My ISX torque is 1950 lbs ft from 1100 to 1700. My cruising rpm is 1330 to 1360. That's right in the middle of my torque. Max HP is 650 hp at 2000 rpm. Cummins has a calculator online that gives the rpm for max mileage. As I remember it showed 1380 as correct for my engine.
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Old 10-20-2018, 04:46 PM   #5
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Hi ! Welcome to IRV2! We're sure glad you joined the gang!

I'm not a Fleetwood guy so can't help with the question. Noticed that you are kinda new on IRV2 and wanted to say hello! Have fun and keep her between the ditches!

Good luck, happy trails, and God bless!
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Old 10-20-2018, 10:21 PM   #6
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What Steve said in post #3
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Old 10-20-2018, 11:25 PM   #7
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Get a Silver Leaf system. It will tell you exactly what your fuel milage is. One guarentee for every 5 mph above 55 mph you will see a drop in fuel milage. Eg. Cummins !SL 370 hp pushing 29800 lbs with a toad at: 55 mph on a flat road 8.5- 9.7 mpg. 60 mph 7.8-8.6 mph. 65 mph 7.1-7.8 mpg.
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Old 10-20-2018, 11:56 PM   #8
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Quote:
Originally Posted by pumper9x9 View Post
Get a Silver Leaf system. It will tell you exactly what your fuel milage is. One guarentee for every 5 mph above 55 mph you will see a drop in fuel milage. Eg. Cummins !SL 370 hp pushing 29800 lbs with a toad at: 55 mph on a flat road 8.5- 9.7 mpg. 60 mph 7.8-8.6 mph. 65 mph 7.1-7.8 mpg.
Silverleaf is built into my rig. My overall average us 7.6, but on flat constant speed I'll see above 12 towing my CR-V. My MH weighs 47,600 empty, has a 54,000# GVWR and a GCVWR of 69,000#'s.
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Old 10-21-2018, 12:15 AM   #9
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You asked about Cat but I am sending you to Cummins because they have answers you should understand. Most answers are not engine brand specific. Cat walked away from the on road business when it got too messy for them. They sell enough stuff for off highway use to ignore the on highway for now.

If you want to understand the issues go here:

https://www.cummins.com/engines/heav...r-fuel-economy

about half way down the page is a button to download a pdf of the Cummins study. It shows you what the issues are at various speeds. One of the things that effect power requirements thus economy is air resistance. That becomes a major factor around 60 mph and is why pushing that flat front box much over that causes a severe hit in fuel usage. There is other information there if you choose to look at it.
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