401 – highway rpm’s

[Lmpy]

I have a 77 cj7 with a 401 out of a 77 Wagoneer. Recently I had new gears installed and it sounds like the engine is going to come apart when it’s running at 2500 RPM’s. The gears I had in for the last 2 years were 2.73 and I just had 4.88 put in. If I were to run 2500 RPM’s with the old 2.73 gears I would be doing 90 MPH. So my real question is what is a safe range to run on the highway or even on the streets with a stock 1977 401?


Thanks for any help you can provide.

Chris

[Goose]

Both of my V-8 amc's turn 2500 to 3000 rpm at highway speeds 65 to 75 mph.. While the fuel mileage bites at this rpm I havent had any problem ..

However I have 3:73 on 33 inch tires in the J-10
and 3:30 (I think) in the CJ-5 on 31's I'm guessing with 4:88 your turning a lot more than 2500 at highway speeds I'm betting 3600 to 4000.. which is a bit more than I would be comfortable with in a daily driver. I treat 6500 as redline on the 360 and 5500 on the 304 (It's kinda tired).so just an opinion but I would guess your spinning her kinda tight.

[Lmpy]

with the 4.88's I would need to be able to run 3200 -3300 RPM @ 65MPH

This isn't my DD but I would like to be able to drive it up to 200 miles away.


With the old 2.73 gears I would shift around 2500 RPM

About 5 years ago I had the 401 with the th400 and the stock 4.09 gears in it and I would cruise 65-75 mph. Now if the qtrac and the th400 were running at 1.00 then that would mean an rpm range of 2700-3150. I just dont remember running the engine that high, but I also didn't have a tach back then :)

[tufcj]

With the 35s and 4.27 gears on my CJ (360), I turn about 3200-3300 at 75 MPH. I've run it on 400+ mile highway trips without a problem. Gas mileage is poor though, only about 10-11 MPG.

I've got 37s on it now, and the 4.27s aren't quite enough gear to pull in the mountains, so the 4.88s go in this winter.

Bob
tufcj

[ibejeepin]

I have 35" boggers on my CJ-7 with a 370. I have 4.10 gears and I'm running around 70@3000 and 75@3200. I judge my speed from my tack instead of the speedometer.
What size tires are you running with the 4.88 gears? :-|

[FrankNB]

Yj, 360 with a 800cfm q-jet and Performer manifold.. 4.10s and 35 boggers..

my last trip to my parents I averaged 14mpg at 45mph... my top speed was about 50mph (80km/h).. around 2700 rpm, and two poser glasspacks exiting right underneath my seat.. Including the humming of the boggers, yes the engine is pretty loud on a 6 hour drive... :shock: