3FE and highway cruising RPMS

[Bryan062087]

I'm in the process of rebuilding my transfer case and debating on whether I want to swap out my auto transmission to a manual. The auto is not in the best shape and slips until its warmed up.

I've got a 4 speed, h42 and was thinking of swapping that in.

I use my truck a lot on the highway and am used to going 75-80 with the a440f at 2500 RPMS.

With 4.11 and 33's and the manual tranny, I would be cruising at a consistent 3000-3200 rpms almost daily. Too much for 3fe? How much increased engine wear would I see as a result of the higher rpms? Gas mileage differences?

I started a similar thread a month or two ago, but never asked this specific question and could not find much relevant info by searching.

Thanks for the help.

 

[RockDoc]

Okay, I'll bite to get things started. I think 3000-3200 is excessive for cruising, and would want to stay below 2800.

I would either go H55F, or swap diffs with a 60 to get the 3.7s

BTW, if you are cruising at 2500 rpm now, the switch will give you closer to 3500 after (2500/0.717), not 3000-3200. You're not going to do 75-80 without overdrive.

 

[Front Range 4x4]

I agree that cruising over 3000 isn't desirable, I have a 3FE, H55F & 4:1's and cruise at about 55mph at 2500rpm which is a nice cruising speed for gas mileage only. 75-80mph is very high rpm for me and gas consumption is scary bad.

 

[Bryan062087]

Not what I wanted to hear but thanks for the input.

Front Range 4x4, you run 2500 RPMS at 55 in 4th right? I don't see why your RPMS would be that high running an h55f and 4.11's in 5th gear? At 70mph, it should be about 2500 correct?

I keep trying to find ways around spending 2k for the h55f, but its not working too well.

 

[RockDoc]

Not what I wanted to hear but thanks for the input.

Front Range 4x4, you run 2500 RPMS at 55 in 4th right? I don't see why your RPMS would be that high running an h55f and 4.11's in 5th gear? At 70mph, it should be about 2500 correct?

I keep trying to find ways around spending 2k for the h55f, but its not working too well.

The H55F doesn't have as tall an overdrive as the A440F does, thats likely why he runs higher revs at highway speed (assuming tires and gears are the same).

 

[Joshua993]

This is all good to know as I have just started doing my own research into swapping in an H55 5 speed and keeping my original 4:11's. The auto in my 62 is running strong right now, and my truck seems to prefer 70 mph +/- at just under 2500 RPMs.

 

[Front Range 4x4]

Front Range 4x4, you run 2500 RPMS at 55 in 4th right? I don't see why your RPMS would be that high running an h55f and 4.11's in 5th gear? At 70mph, it should be about 2500 correct?

i have 33's so at 2500rpm in 4th I'm at 55 and 5th is 65.

 

[Bryan062087]

Just thinking, isnt a 2f set up to run 3k rpms at 70 from the factory? Only a small percentage of 60 owners have a 5 speed...

Its ok for a 2f to run at these rpms but not a 3fe?

 

[Front Range 4x4]

I'm not saying anything about the 2F since I don't know anything about them. 3+K on the 3FE is common for me running up the hills. I was referring to mpg conservation on keeping it around 2500rpms.

 

[mkaustin]

We've had an H42 4-speed in our 'Cruiser for the past 4 years. With 31" tires, I run about 2950RPM at a true 65MPH
We had 177.8K when the H42 was swapped in and we have 222.4K on it now. So that's almost 45K in the last 4 years and a lot of it has been on the highway. I get better MPG now w/ the H42 than I ever did w/ the A440F.
W/ 33" tires I expect to get about 8% reduction in RPMs and that will put my SpeedO and OdO spot on. Running 2715RPM at 65MPH. BTW current MPG is about 15. w/ the A440F it was about 12.

 

[RockDoc]

I guess it all comes down to preference. Mine runs 2300-2600 on the highway depending on speed I'm running, but I have no issue taking it up beyond 3500 on hills. I would imagine running at higher rpm would wear things out a touch faster (relative I suppose for an engine that'll get 300 000 miles). Sounds like for fuel consumption it is vehicle speed that is the biggest factor. If I run mine around 65-70 mph, I can get 15 mpg, if I run 75-80 mph, milage takes a real dive.

 

[esh]

33s/4.11/A440, I think I'm at 2200 at 65mph. Because it is so loaded down (think it is up to 6200lbs), I will run it up to 4,000 rpms/65mph in 3rd gear and it is quite smooth, usually carrying 50mph over a good hill. Best I got with 31s and without all the weight/height was 19mpg. As soon as I got up in elevation where the truck had previously lived it would get 17mpg normally. It now gets about 15-16 on trips.

Hmm the info about the H55 OD gear height is interesting stuff. Another data point for possible swaps. The 1HZ likes to make power at lower rpms... the Aussie extreme valve body and billet torque converter, with a large cooler should keep temps down.

 

[euclid]

315's/4:88/A440F. Pretty much the rest of my numbers are the same as Esh. I'll run mine up to 4K to pull a long hill occasionaly, especially since my valve body keeps my torque converter locked up in 3rd, but it sure screams at 4K.

I woulnd't want to run an old tired 3FE at 3K + all the time. H55 is the better choice if you can swing it. If not, stick the H42 in and start saving for an engine.

 

[Bryan062087]

Thanks for the replies everyone. Looks like constant 3k rpms is not a good idea.