I read somewhere in here that the engine RPM @ 70mph on a 5spd is around 1850-1900. On my 47RE I have right at 1950-2K. The individuals signature didn't have anything about tires or gears in the rear.
Is the 2K number right for the auto @ 70 or is my trans done.

 

The speedo hasn't been reprogramed for the tires. I know that I'm off about 6-7mph at 70 indicated. Just wondering about RPM at different speeds.

 

Give that a try, I think you'll like it.
http://www.grimmjeeper.com/gears.html

 

It all depends on what your gear ratio is. I have 3.54 gearing and 35's. In overdrive, locked at 70 mph, I'm down around 1700 to 1800 rpms.

 

U have 4.10's according to the gear calculator I have.

And for ur tire size, and trans, u should be going (in overdrive)
70 @ 2000 rpm
61 @ 1750 rpm
52 @ 1500 rpm

So try to have someone trail you on the phone or with a gps to see if ur speed is what it's suppose to be. Because with 3.54 gears u'd be going 80 @ 2000, so i think u'd notice if ur going that fast at that rpm, so it sounds like u have 4.10's and all seems like it should.

 

My 97 with auto, 4.10's and 265s at 2000 rpms is at 62 mph or so. 70 puts me at 2250 I think.

 

A 4.10 rearend should run right around 2000 rpms at 60....my 97 ran those numbers with 265s. redwake

 

thats with a 5spd and somewhat stock tires ^. The auto has a higher overdrive ratio, i think it's like 67@2000 with 235/85/16's.

 

My build sheet from the dodge house says, 3.54 gears. I was really wondering about the difference between 47RE and 5spd rpm's at certian speeds, 60 or 70 with the same tires and gears. I know that will be hard to come by with the way that people modify their trucks around here.

 

i'll do ur tire size and 3.54 gears and compare the actual speeds and rpms, not what ur uncorrected speedo reads.

285/75/16 tires

47rh/re Auto (3.54 gears)

2000rpm @ 80mph
1500rpm @ 60mph

5psd Manual (3.54 gears) same size tire

2000rpm @ 74mph
1500rpm @ 55mph

hope thats what ur looking for.

 

Using the calculator I posted:
@65mph, with 285-75-16's and 3.54 gears
The auto equiped truck in overdrive with the converter locked the rpms should be 1625.
A 5 speed equiped truck should be around 1766 rpm's in 5th gear at the same speed.

 

MCC2430 - You are correct....the 5 speed in 5th is a shorter gear than the OD on an Automatic.

6th on a 6 speed is almost identical to OD on an Auto (.69).

RJ

 

They're close,
Overdrive ratio for the different transmissions,
Auto is .69
NV5600 (6 speed) is .73
NV4500 (5 speed) is .75

 

Actually not as close as I thought...driving them!
6th gear and OD in an AUTO feel the same. 5th in a 5 speed compared to Overdrive feels very different...to me.

RJ

 

So in OD on an auto you're actually pushing less rpm's than 6th gear going the same speed?