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Old 03-27-2016, 06:43 PM   #1
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Best RPM for economy CAT C7

The following spec recommendations are for vehicles
that are 50,000 lbs. or less GVW or GCW.
• For the best balance of performance and
economy, spec axle ratios and tire size to obtain
2000 rpm @ 60 mph (97 km/hr).

Found that on this site: http://www.toromontcat.com/truck/pdf...EDT7014-01.pdf

Anyone agree or disagree? Or have other formulas?
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Old 03-27-2016, 06:46 PM   #2
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RPM's sound really high for 60 MPH Bob?
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Old 03-27-2016, 07:11 PM   #3
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My C-9 runs around 1600rpm doing 60, that does seem high.
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Old 03-27-2016, 07:17 PM   #4
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Usually the calculations for economy posted are for heavy trucks weighing more than RV's so they aren't necessarily true for lighter vehicles.
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Old 03-27-2016, 07:22 PM   #5
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I have a C-9 and I run 65mph at 1700 rpms. That does sound high for your case.
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Old 03-27-2016, 07:34 PM   #6
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I am no expert. I have heard from people who I do consider expert that a CAT engine usually gets it's best fuel economy at 1200 RPM. For most, if not all, that is somewhere in the 50-58 MPH range. Again, that's hearsay! I have found it to be true in my case.
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Old 03-27-2016, 09:42 PM   #7
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The brochure says "for best balance of performance and economy" and pertains to gearing options for the C7 on vehicles less than 50,000 lbs.
It also pertains to all iterations of that engine from 210 hp and 520 lb-ft of torque all the way up to 360 hp and 925 lb-ft of torque.

I read it as sort of a blanket statement for a lot of different applications and wouldn't read too much into it...
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Old 03-28-2016, 10:57 AM   #8
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My CAT C13 makes the best torque at around 1300rpm. I usually run at around 1450 at 60-62mph. I pull my hills while cruise is set at 62 and end up at the top of the grade usually in 5th slightly lugging the engine at about 52mph for a 6% grade.
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Old 03-29-2016, 08:47 PM   #9
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my 3126b runs at 1750 RPM's at 62 MPH in our Sport Chassis truck
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Old 03-30-2016, 06:45 AM   #10
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Best performance

Best efficiency on a diesel should be at or slightly above max torque RPM.
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Old 03-30-2016, 07:46 AM   #11
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Quote:
Originally Posted by wb7auk View Post
Best efficiency on a diesel should be at or slightly above max torque RPM.

This is absolutely the best answer in the thread. As max torque rpm is engine size/model specific, a hard rpm number for all diesels doesn't exist.
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Old 03-30-2016, 08:42 AM   #12
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My Cat book says my c7 engine is most efficient between 1400 and 2000 rpm, or 1700+/-300 as my pee brain handles it. Take whatever safe speed that yields. The fuel efficiency differences within this range are negligible, and not worth my consideration. Of course, my family's safety is more important than anything else, so a safe speed for the road and weather conditions is WAY more important than maximizing my fuel.
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Old 03-30-2016, 05:33 PM   #13
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Quote:
Originally Posted by 1ciderdog View Post
The following spec recommendations are for vehicles
that are 50,000 lbs. or less GVW or GCW.
• For the best balance of performance and
economy, spec axle ratios and tire size to obtain
2000 rpm @ 60 mph (97 km/hr).

Found that on this site: http://www.toromontcat.com/truck/pdf...EDT7014-01.pdf

Anyone agree or disagree? Or have other formulas?

I would be in 5th gear @ 2000 rpm's @ 60 mph. I try to keep my speed b/t 60-62 mph in 6th gear @ 1650 rpm's. That works for me.
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Old 03-31-2016, 01:13 PM   #14
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Quote:
Originally Posted by wb7auk View Post
Best efficiency on a diesel should be at or slightly above max torque RPM.
According to a chart in this attachment max torque on a 330 C-7 is 1440 rpm. http://www.rvtechlibrary.com/engine/Cat_C7_Specs.pdf
So running 1500 rpm would put me in the slow lane all the time. I haven't driven for a couple of months but if I remember correctly 1800 rpm is about 60 mph - but I could be wrong, memory isn't as good as it used to be. I'll be on the road in a couple of weeks and will try to write down the RPM & mph.
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