Drivetrain combo

[EPK5]

I am in the process of revamping my 78 for driveability and capability. I am looking at running the 700r4 and the NP241 transfer case. Is this a viable setup or too much of a hybrid? I know that the 700 isn't the most popular tranny but I like the simplicity and the overdrive. It is going behind an old school small block so I don't see myself over powering it. Eventually I will be adding 3/4 ton axles but for now I am running the stockers with 35" tires. Thanks fellers.

 

[ryoken]

what gears are in it?

keep in mind with 35's, 700's do not like undergearing, they either hunt for OD, or never get into it.. not a healthy existence for that trans to be lugging...

 

[swettysblazer]

My truck is a 1991 with the same combo.... 350/700/NP241. I am running 37's with 3.73's, and like Ryoken said you need to be aware that OD will be basically useless unless you regear. I have wheeled the snot out of my truck and have had no issues whatsoever with this combo.

 

[EPK5]

I have 4.10s in it.

 

[EPK5]

At 65 mph the truck is turning about 2700-2800 rpm. It is screaming by 70 mph. I live in Texas, the land of 75 mph speed limits.

 

[swettysblazer]

What are your plans for the truck in the future besides the 3/4 tons? Wheeler?

 

[tRustyK5]

The 700R-4 will get your freeway R's down to 1800 at 65 mph. Probably tolerable for OD, although 4.56's would still be better. 4.56's and a 700R4 would put the R's at 2000 at 65 mph.

 

[EPK5]

Swettysblazer, I plan on a reliable adventure, medium duty wheeler, I don't have a large surplus of funds so I don't plan on going too crazy, the crazier it is the more it hurts when it breaks. I plan on sometime doing an LS swap of some sort but that is not a huge priority.

tRustyK5, I am hesitant to swap gears out just yet, especially since I plan to go heavy on the axles. Can a 700r4 survive at that low of an rpm? Lugging a 700r4 is bad juju.

 

[swettysblazer]

Swettysblazer, I plan on a reliable adventure, medium duty wheeler, I don't have a large surplus of funds so I don't plan on going too crazy, the crazier it is the more it hurts when it breaks. I plan on sometime doing an LS swap of some sort but that is not a huge priority.

tRustyK5, I am hesitant to swap gears out just yet, especially since I plan to go heavy on the axles. Can a 700r4 survive at that low of an rpm? Lugging a 700r4 is bad juju.

I would go play around with the GrimmJeeper gear calculator to see where you want your desired RPM to be. You can find it on google

 

[EPK5]

Advice on proper rpm? Almost bone stock 350, Edelbrock 650 cfm, MSD Pro billet dist, hotter Accel plugs and wires and headers, other than that nothing done to it. I am cool with 65-70 mph, saves wear and tear in the long run. I sincerely appreciate the input guys. I have been wheeling for over 20 years but I always appreciate an outside perspective.

 

[swettysblazer]

I feel like anywhere between 2000-2200 would be good. This way you're not hunting for OD and still bearable on the highway.

For example, my truck at 70 would be running 1600 RPM.... wayyyyyyy too low for me.

 

[tRustyK5]

I feel like anywhere between 2000-2200 would be good. This way you're not hunting for OD and still bearable on the highway.

For example, my truck at 70 would be running 1600 RPM.... wayyyyyyy too low for me.

4.56's...

Formula is easy:

Speed (mph) x rear end ratio x final drive (700R-4 is .70:1) x 336 (for a lock up auto or manual trans) / tire diameter (inches)

For a non lock-up auto you use 355 in place of 336.

TH 350 and 4.10's at 65 looks like this:

65 x 4.10 x 1.00 x 355 / 35 = 2703 rpm

With 700R-4:

65 x 4.10 x 0.70 x 336 / 35 = 1790 rpm

700R-4 and 4.56's:

65 x 4.56 x 0.70 x 336 /35 = 1991 rpm

As you can see to hit the 2000-2200 cruise rpm range you'll need 4.56's or even 4.88's.

Frankly 5.13's are still decent... 2240 rpm at 65 mph.

 

[ryoken]

4.56's...

Formula is easy:

Speed (mph) x rear end ratio x final drive (700R-4 is .70:1) x 336 (for a lock up auto or manual trans) / tire diameter (inches)

For a non lock-up auto you use 355 in place of 336.

TH 350 and 4.10's at 65 looks like this:

65 x 4.10 x 1.00 x 355 / 35 = 2703 rpm

With 700R-4:

65 x 4.10 x 0.70 x 336 / 35 = 1790 rpm

700R-4 and 4.56's:

65 x 4.56 x 0.70 x 336 /35 = 1991 rpm

As you can see to hit the 2000-2200 cruise rpm range you'll need 4.56's or even 4.88's.

Frankly 5.13's are still decent... 2240 rpm at 65 mph.

yup, it's not TBI.. it's a carb, the cam is a little more conducive to actually SPINNING, than the anemic TBI pimplestick.. powerband is a smidge higher...

 

[EPK5]

So the hunt for bargain 4.56s begin. I was hoping to sneak by with the 4.10s.

 

[EPK5]

I'm one of those Craigslist perusers, I like a good deal on parts.