MPH vs RPM's

MooseMeat · **Posted:** Tue Nov 07, 2006 2:33 pm

ok I just wanted to ask what everyone is turning for rpm's vs mph.

My 2006 CRD:

At 70 mph it's turning just a hair under 2000 rpm's.

At 60 mph it's turning 1850 rpm's.

If I take it to around 65 then slow it down to 60 mph it will run at 1700 rpm's.

Trying to figure if this has anything to do with fuel mileage.

BiodieselJeep.com · **Posted:** Tue Nov 07, 2006 4:39 pm

There was a lot of discussion on this in the spring (I think?) especially in relation to brake specific fuel consumption and mpg. You shifting sound about right. The BSC curve showed a "sweet stop" at 2000rpm, and so there was thinking that at lower speed you should turn off the OD to get close to 2000rpms. Also, as you go faster, the wind resistance increases as a square of your speed....so I generally keep it at 2000rpms if I want to save (bio) diesel. But 80mph gets you there SOOOO much faster.

2005 CRD

2000rpm = 68mph = 25.6 mpg
2250rpm =75mph =~22mpg

BLake · **Posted:** Tue Nov 07, 2006 7:10 pm

Your observations are correct. You have to speed up to 65 to get it into top gear. You can slow down to about 60 and it will stay in gear. Anything under that and it will kick down to 4th gear. 1800-2000 RPMs is the sweet spot for mileage.

An interesting tidbit. When my Scangauge is working, the Intake Air Temp (IAT) is about 110-120 degrees in top gear and 60 MPH. When in 4th gear at the same speed, the IAT zooms to 150-160 degrees. Boost pressure is about the same in both gears so should be no difference in heat gain from compression. I think the EGR is opening in 4th gear and locked out in 5th. After the last reflash (F31) the tranny kicks down to 4th gear much more readily. Wonder if the EPA got after Jeep for emissions?

jinstall · **Posted:** Wed Nov 08, 2006 10:14 am

@ 110mph RPM 3200 and I really don't care about milage.

litton · **Posted:** Wed Nov 08, 2006 11:50 am

BLake wrote:

Your observations are correct. You have to speed up to 65 to get it into top gear. You can slow down to about 60 and it will stay in gear. Anything under that and it will kick down to 4th gear. 1800-2000 RPMs is the sweet spot for mileage.

An interesting tidbit. When my Scangauge is working, the Intake Air Temp (IAT) is about 110-120 degrees in top gear and 60 MPH. When in 4th gear at the same speed, the IAT zooms to 150-160 degrees. Boost pressure is about the same in both gears so should be no difference in heat gain from compression. I think the EGR is opening in 4th gear and locked out in 5th. After the last reflash (F31) the tranny kicks down to 4th gear much more readily. Wonder if the EPA got after Jeep for emissions?

After my F31 flash, I noticed the same thing. I don't think it's shifting to 4th as much as the torque converter is unlocking.

BLake · **Posted:** Wed Nov 08, 2006 12:52 pm

TC, 4th gear, 5th gear??? Who really knows. You would need a scan tool to verify what it is doing. There are no chart I can find in the service manual that describe what the tranny is supposed to do.

action · **Posted:** Thu Nov 09, 2006 10:02 am

Highway, ~110 to 115 kph, ~2000 RPM...we have alot of hilly terrain and this torque monster just motors on up without loosing speed or changing RPM!!! Now towing with a full load it will downshift on the hills but not for long. I love this truck!!!

KenJennings · **Posted:** Thu Nov 09, 2006 10:25 am

This is from the spedometer which may be off by a few mph per other threads:

In overdrive:

2000 rpm == 71mph
1900 rpm == 67mph
1800 rpm == 64mph

about 1620rpm == 58mph (as slow as it goes in overdrive)

Zonie · **Posted:** Thu Nov 09, 2006 6:34 pm

@ 115 mph 3300 rpm and that's all I could get out of her on a flat road

jinstall · **Posted:** Wed Nov 15, 2006 12:26 pm

How far did you drive at 115 mph?

Zonie · **Posted:** Sat Nov 18, 2006 10:13 pm

I'm not sure, I wasn't looking at the odometer. Far enough to stretch my luck with the California Highway Patrol.....

MPH vs RPM's

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