Danger RPM for highway driving

[motormayhem]

Well I have a dana 44/14 bolt corporate setup that I am going to buy if the gears are right. It has 4.10 gears in it. My question is will my m1009 still be able to maintain 75mph on the highway for hours or driving with 35" BFGs and the 4.10 gears and without hurting the engine or causing it to wear excessively due to sustained high rpm?

 

[fstfrdy]

with 410s and 35s you should be close to stock rpm. most civvy trks came with 373 gears and 30 in tires so you should be running close to the rpm as stock maybe even a touch lower

 

[kennyw]

Use this website to compare what you have to what you want:

Gear Ratio Calculator

 

[motormayhem]

I looked at the gear ratio site, but I was just wondering rpm wise what is a safe rpm for the engine at highway speeds. Cause it looks like the engine will be doing about 3100 at 75 with the 4.10's and that seems a little close to the red line.

 

[kennyw]

I believe the governor is set to 3200 RPM, you can run at the governor all day long if you want, but don't expect any kind of mileage. That is also a good RPM to kill the 6.2L if the bottom end is starting to crack in the crank or block.

You will definitely not be happy with running 3100 RPM on the highway. I am running 37" Hummer tires on 4.10 axles and 60 mph is comfortable, 70 mph can be done in short bursts.

 

[motormayhem]

Well I ended up getting a whole blazer minus the motor for $400 with many extras including a np203, manual tranny, 2 extra doors, np205, roll bar, 4" lift, dana 44/14bolt FF with 4.10s. I was gonna go with 3.73's but this was too good to pass up. Do you think I will able to do 65 without hurting the motor?

 

[91W350]

While the engine produces maximum horsepower at 3,400 rpm, it produces maximum torque at 2,000. If you are wanting to cruise at 65-75mph, you will want a gear/tire combination that will do that at 2,000 rpm or just a little over, 2,400 at the most. To run extended time much higher than that will pound your 6.2 to death. These engines were beautiful for what they were designed for, but rpm was never their intended design. That said, they scream rpm wise for a diesel in their era. Cummins was not out yet, but they typically were governed below 2650 in the early years. The Powerstroke was not much higher. I think the civilian 6.2 engines are governed lower that their military counterparts. If you can hit the 2000-2400 rpm slot, you will probably see your best fuel economy. The 6.2 has an extremely high compression ratio and an unusually small rod for the application.

 

[motormayhem]

Well it is gonna get 4.10's which should be fine for town driving between 45-55 and the occasional (maybe twice a year) 60 mph trip to the mountains 200 mi away. The gear ratio calc I used says 2495 at 60 so that looks ok in my inexperienced opinion, right? I don't need a speed demon just something with the balls to get itself up hills and reliably get me there and back. I think eventually I will get 37's so the 4.10's will be better suited for that when I get them.... If only the th400 had an overdrive and was still as stout of a transmission.

 

[kennyw]

I just took my truck on a 3000 mile road trip hauling a small flatbed with my motorcycle on it. I stayed at 60-65 mph the whole time. I was happy with how my truck did on the long drive until I hit a mountain pass. However, it would be nicer if I had an OD transmission, that would have put me in a more comfortable position.

I should also note, my truck is a civi version, so I have more noise reduction than an M1008/M1009. I can't talk on a cell phone while I'm driving unless all of the windows are rolled up. Even then it is difficult to hear.

It is possible to run a 4L80E behind the 6.2L if you get the stand alone wiring harness and computer from a 1991 K30 crewcab or K20 Suburban with a 6.2/4L80E combo.