I admit that I never travel at the speed limit. Being a motor head and speed demon , Im wondering if im inducing premature engine wear by traveling in the high rpms. It seems that the 4:10 rears are comfortable w/ traveling at around 70 mph w/ rpms at 2600. I sometimes travel at 90 mph w/ rpms at 3000 or so . . Is this bad, and should look into taller tires or different rears. I only tow a 25' boat on occassion so low gears are not that important, but i do like the torque response w/ lower gears. Any info would be great

 

I know on the 2nd gen 24 valves, you werent supposed to exceed 3K for more than 30 seconds, not sure bout the 3rd gen CR's. Might wanna back it down a little.

I noticed that too though when I test drove a 6spd w/4.10's (salesman was looked kinda nervous ) . Even in 6th at 80 it seemed to be turning way to many RPM's.

Jeff

 

that is the one thing that i didn't like about my 03 H.O. it also had 4:10 gears in it and about 70 mph it almost felt like it was running out of steam. would tow like h*&% but wouldn't go very fast. about 75mph is all i was willing to go and if i remember right the rpms were about 2500. seemed to much to me and can't be good for the engine in the long run. JMHO


britt

 

You're not gonna hurt it. In medium duty trucks the 5.9 is usually limited to around 65 mpg by the gearing, so they run around all day wound out and they still average 300k between overhauls. Run as fast as you want, you won't hurt the motor.

 

??????

70 MPH is 2350 RPM with the 6-speed and 4.10s in my truck. I will run 75 MPH (2500 RPM) all day on the Interstate pulling our 5th wheel RV, and the only thing it hurts is my wallet when I have to fill the tank. Having said that, I don't know if I would want to run 3000 RPM all day just from the noise factor - have you considered a U.S. Gear overdrive unit?

Rusty

 

Just the idea I used when I picked my 04.5. I know a bunch of folks who are very happy with the 3.54 gears in older trucks (even when towing). So..... when I found you could not get the 3.54s I got the 3.73s and put H2 wheels and 315s on it as soom as I got home. Now crusing at 80+ (It's great to live out west) is a low rpm deal. I hav not tried to tow anything heavy yet as she is still pretty new, but approx 8k TT and stuff in the bed the cruse control holds 80 in 6th gear with no problems.

Have a great day!
Allen

 

hmmm, I also have the 3.73's and H2 wheels with the 315's. I commonly run about 2800-2900 RPM. I guess I should check the speedo once in a while...

 

You bet ya, I haven't had my spedo recalled yet and use my GPS to verify speed and keep my drivers license!

 

When I bought my truck I wanted the 4.10 gears. If you install 315's which equate to a 34.5 in tire on your truck. With 4.10's you will be running 3.68 road gear ratio. By the same token, if you have 3.73 gears you will have a 3.28 road gear ratio. So for the best of everything, towing, highway. IMO 4.10's are the way to go.
Deano

 

I think the 3.73 gears are great with the 6-speed. I am never feeling lacking in the towing department. The 4.10s I think would induce way too much shifting for my own sanity, and I don't haul a load heavy enough to justify it.

Personally, the highest I would cruise with this motor is 2500 rpms or so. The medium duty trucks run lower revs than ours do, I believe 2700 rpm or so redline according to the Cummins website. If you want to run faster, get a truck with a 3.73. Personally, I would have liked to get a 3.55 in back like the older trucks had. When I get on the highway I always have this feeling that there should be a 7th gear there... the engine certainly has the torque. But hey, that's just me. I love torque!

 

Deano, those numbers seem to be a bit excessive. Please let us know how you computed them.

If running your motor at 3K was bad, Cummins would have put the rev limiter there, and not higher as it is. You have to understand that the engineers are going to be conservative where they place the rev limiter, just for safety, and reliability sake.

So, I hear people saying to run at 3K RPM. Are you same people going to only tell him that he should only tow 5K lbs, because while his truck can go higher, that he shouldn't chance breaking anything?

 

I ran mine up to 105 mph for about 15 minutes and no parts came out. You could run that motor at 3000 all day and not hurt it. Just keep filling the tank.

Casey