johnjudge

:I just bought a new and my first diesel truck, I was wondering what RPM I am supposed to cruz at? The tack says around 3100 is redline, but to go 70 on the highway I have to be at almost 2500 constant, is that ok? ???

Shovelhead

Welcome John,
The Cummins is designed to run at, or near redline for hours and hours.

My '99 with 4.10 rear gear tachs approx 2400 rpm @ 70 and will run like that without breaking a sweat until it runs outta fuel.

Ed

Mexstan

I regularly cruise at 2500 rpm. Fuel consumption goes down a bit, but still not bad.

doug

I understand that the CTD falls apart at 4200. So that 3100 rpm redline has lots o margin in it. Ed is right -- the engine just blinks, smiles and pulls like a billygoat at 3000 rpm. you know what they say 'run it like you stole it'.

EdsGarage

I bought my first CTD 1000 miles ago and I am in the same boat.

At 2000 RPM, I am going 65 MPH. AT 70 MPH it begins to approach 2300 RPM. The engine sounds as though it wants another gear. I panicked.

After posting my concerns and getting feedback, I realize that it is not out of the ordinary. In my case the 4:10 is the main culprit. Having never driven the 3:73, I cannot compare the two.

Hang in there and check those body plugs!

bulabula

I still find myself looking for 7th gear once in a while.

drafalske

Poor guys... I got the 3.55's in my truck. Cruising at 70 I'm right at 2000 RPM.
-D

doug

[quote author=EdsGarage link=board=17;threadid=17830;start=0#msg166956 date=1059753142]
Having never driven the 3:73, I cannot compare the two.
[/quote]
going from 4.10 down to 3.73 is a 9% change. in your case, 65mph @ 2000 would change to 65 mph @ 1820. I'd say for a towing animal, you're better off with 4.10s, cause 1820 is kind of on the low end of things if you're towing 16,000 lbs.

I happen to like my 6-speed/3.73 and 285/70 tires. I'm looking at 65mph @ 1900, which is right where the CTD likes to run for best fuel econmy. At least for the 2nd gens anyway. it will be interesting to see if the fuel economy rpm band is any wider with the new HPCR. Its possible that the new engines might not loose fuel economy as fast as you increase rpms but I don't know...

GrandpasRam

Mine's turning 2150 at 70MPH, and feels like it would like to have another 200 RPM to cruise with. I just don't like doing over 70 in Dallas traffic, so 2150 it is most of the time. Cruising at 2500 should have no adverse affect on the engine, only on MPG.

doug

hey grandpasram -- do you have any pics of your guage install?

GrandpasRam

[quote author=Doug link=board=17;threadid=17830;start=0#msg166972 date=1059754144]
hey grandpasram -- do you have any pics of your guage install?
[/quote]

I don't have a digital camera, so I'm afraid not. They look like any of the pillar mounts you'll see in this forum, and are the ISSPRO EV (extreme visibility) guages, which I like very much. My kids get all my available "disposable income", so I haven't yet been able to afford a digital camera and download pics of my rig. I will try to do that over the next few weeks with a loaner camer from my huntin' buddy.

johnjudge

thanks for the great response to my question! I was thinking of changing the size of the tire, I was told that if I went to a 33" tire that would be the same as changing the rearend to a 373, does make sense? But I was also told that the speedo would be off, any fix for that. thanks

gadgets

The speedo, & everything else that relys on accurate speed, will be off, but only about 10% or so....

SuperLift makes a TruSpeed calibrator, but they don't have one yet for the 2003 diesel; everytime I call, I get a different answer as to availability.... >

They've said anytime from this week to next year.... :

If anyone knows of another mfg, please post it!!

Rene