is high rpm hwy running harmful?

[wide body]

my rig has 4.30s in it. so at 70mph it's running right around 2300rpm. the speed limit out here is 70 between here and CA and 75 between here and UT. if read correctly, the redline on this motor is 3700? will i hurt this motor by running it 70-75 for long periods of time? i wouldn't think so, but i just wanted some of your opinions. also, if the cutoff is at 3700rpm why doesn't the truck run the motor to that point before shifting when i run it hard? it seems to shift at 3200rpm or maybe just over. normal?

[Dim Sum]

The 3700 rpm redline is there for going downhill and using the engine to help brake the truck. When you look at dynos of this engine, the power really drops off after 3k, so you really have nothing to gain by running the engine at those speeds.

The engine should have no problem running at 2300 rpm. I would make sure to keep an eye on the coolant and make sure you test the coolant to make sure it is within Ford's spec's (nitrite levels and anti-cavitation additives) as the higher speeds mean faster running water pump.

[colo_dually]

I have 4:30's in my truck, with a considerable number of highway miles running around 65-70 mph. 70 is around 2300rpms for my truck as well, and I will open it up and run 75/2500rpms when the law allows. I haven't had any issues that I feel were brought about running those speeds.

[Beatngu]

Look at equipment such as farm and construction.

Red line on most is 3000 rpm's and they operate near red line for hours at a time.

I say your fine

[eastboundown6]

Ive seen several overspeed test engines that revved to 3700 for anywhere from 500 to 1000 cycles without significant wear

[6.4_twins]

The engine should have no problem running at 2300 rpm. I would make sure to keep an eye on the coolant and make sure you test the coolant to make sure it is within Ford's spec's (nitrite levels and anti-cavitation additives) as the higher speeds mean faster running water pump.

So true, its very important to keep an eye on this.

[wide body]

thanx for the input, much appreciated!

[rberg31]

Originally Posted by Dim Sum

The 3700 rpm redline is there for going downhill and using the engine to help brake the truck. When you look at dynos of this engine, the power really drops off after 3k, so you really have nothing to gain by running the engine at those speeds.

The engine should have no problem running at 2300 rpm. I would make sure to keep an eye on the coolant and make sure you test the coolant to make sure it is within Ford's spec's (nitrite levels and anti-cavitation additives) as the higher speeds mean faster running water pump.

I'm not sure if this is off topic, but what would you say is the optimum rpm to run a 6.4L for an extended period of time? Seems like i get my best fuel economy between 55 and 60mph which equates to 1600-1800rpm on my set-up.