towing with a three speed auto

[obijuan]

so i am going to be towing my blazer all across texas in the next few years, with my dually. 1984 454/brand new stock rebuild th400/np205. got a good trans cooler and oil cooler, and my rear bumper reciever is set to go.

ive got dana 60/70 3.73s and 36s now planning on 37s, and its a turd. can go 4.10s pretty easily and am trying to get 4.56 in the bag.

i am leaning towards 4.56 but i just remember how high my rpms were on the k5 when i had 350/400/205 4.56 and 37s. i could barely go 65 without feeling like the gas tank had a leak and wondering where my fuel went!

ive calmed down, with the dually and only hot rod it when the music is up.

whats a good towing RPM for my 454 to be at for say, 6 hours straight. thatll get me to dallas.
also whats a good cruising rpm to be at not towing anything. typically i will be unloaded. maybe wheel five times a year.

ive got a 20 foot steel car hauler, so add a 1 ton k5 on it and full o spare parts and at least 70 gallons of fuel.

give a towing noob some advice thanks guys.

 

[K5er4Life]

I would probably go with the 4.56's. Just to make it easier on the truck/tranny/sanity for the tow. However, at 65 you will be turning probably around 2600 rpms. Which I do believe will put you close to what the stock setup would be at 65. 4.10's would be good for the daily driving around town stuff but you have a dually and sounds like you would like to use it, so I would go with 4.56. The best option if you can afford is to go with a 4.56 and a 4l80 or an easier swap would be to add a gear vendors to the back of the 205. That way you can have the best of both worlds, cruising on the freeway unloaded 65 mph at 2100 rpms, then switch off the gv for heavy towing.

Or you can leave the 4.10's and run it and more than likely you wont hurt that th400. With heavy towing I do like a small shift kit in the tranny to boost line pressures a little to keep the tranny from slipping so much (less heat) and provide slightly firmer shifts (less heat).

 

[throttleissues]

4.56s aren't going to put the RPM too high with 37s, considering they were stock in both of my 3 speed auto Chevy trucks. Just go with the 4.56s, you'll be happy you did, especially with the tall 1st gear in a th400.

 

[obijuan]

cool, thats what i was really thinking. and hell if i get an awesome deal on a 4l80 or OD unit even better. i just need to find a powerlock for 4.56 and up.

also i bought a shift kit but i didnt read the directions. built the trans and got to the valve body area, and forgot a few internal parts.so i just built it stock. itll do for a long time. just next one ill read the directions!

 

[tRustyK5]

What is the tq peak for that engine? In an ideal world you'd be towing at the tq peak rpm for most of the time. I'd go out on a limb and guess that magic number is somewhere around 2500 rpm, maybe even 3000 rpm. 4.56's will get you there, but it won't be easy on fuel.

Rene