Stock M715 at Highway speeds

[M715up]

I have a M715 all stock and would like to know how to make it go highway speeds (75,80mph). And how much would it cost?

[Nuke_mcinfantry]

new engine, 4400rpm at 80mph 36 inch tires (stock)
new engine, 4100rpm " " 38.5inch tires
new engine, overdrive tranny 3200rpm at 80mph 36 inch tires
" " 3000rpm at 80mph 38.5" tires

it costs as much as you are willing to spend, beg, trade and fabricate. to pay someone? who knows.
if you could get a free motor and tranny and can weld i guess a few hundred though

[brute4c]

Lets see....before you get to the drivetrsin, you need to completely redo the steering and braking systems to be up to the challenge of doing 75-80 MPH....once you figure that all out, you can go a couple ways:
new higher reving motor, OD tranny, bigger tires
new higher reving motor, OD tranny, higher axle gears
new higher reving motor, bigger tires, higher axle gears
new higher reving motor, real huge tires
new higher reving motor, mega high axle gears
new higher reving motor, overdrive/underdrive unit, possible gears or tire swap depending on OD ratio
new higher reving motor, OD unit added in front of tranny or behind as a seperate gearbox, like gearvendors for example, still need bigger tires or higher gears or an OD tranny with it.

Basically, if you want to have your highway RPM's down to say 3000 rpms or so at 80, you need to change your final drive ratio from 5.87 stock to roughly 3.80 gears...not accounting for any losses in a torque converter or other driveline losses. Changing tire size is basically altering the gear ratio just like swapping to a different trans with od, or other od device, or changing axle gears, etc....oh and by the way, the stock tcase woud be pretty suspect at those kind of speeds sustained.
So lets see...the steering, brakes, engine, trans, tcase, axle ratio or whole axles, tires and wheels need to be changed or modified....of course the wiring will need adjustments...and the aerodynamics play so well in your favor, not to mention the high center of gravity...
can you say $$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$ $$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$?
brute4c

[M715up]

What type of engine and Over Drive?

[Nuke_mcinfantry]

brute, whats wrong with the steering?

[brute4c]

Well my opinio is that the stock steering isnt the best suited to running 80 MPH all day....the gear boxs tend to wear, the caster is built into the axle...something I like to set up a bit for high speed driving....
Also for the higher speeds....possibly bigger tires.....steering stabilizer(s) would be in order....
brute4c

[brute4c]

What type of engine depends on what you want...on the bottom end, the 292 chevy and 300 ford 6 cylinders have been used and they provide good power with stock gearing...big od's probably would need more...might be looking at something with good rpm manners from 3-4000 rpms....making good torque to pull a big overdrive, and at least 300 horse I would guess...the more the merrier....
Gear Vendors makes an overdrive....their is one that goes infront of the stock T98 tranny, if you keep that....BrownLipe over/underdrive boxes give a low range, 1:1 range and overdrive range....but the only ones I have ever found with big OD ratios are WAY too big for the M715...like might not even fit between the frame rails....and way too heavy.....lots of OD treannies out there....
Manuals like the NV4500
Autos like the 700R4 gm, AOD ford, A500/A518/A618 Dodge, etc.
Could get cute and try a Viper or corvette tranny...6 speeds with OD.....
If you try to do it on tranny ratio alone, you need a top gear in the tranny around .65 or so....
Personally, I am (hopefully if I ever spend 10 minutes not on injured reserve) working on a 400 Dodge big block, short stroke but good power, A518 Dodge OD tranny, .69 top gear with a 2.74 low gear, NP205 tcase with 3 to 1 low gear set, a Klune V underdrive with 4 to 1 low range, stock axle gears, and 38 inch tires....my truck will see highway...up to 70 max, and a lot of trail use especially with the troop seats full of my kids....a good reason to have a ton of low gearing
This should give me all I need on the top end and the bottom end....remember if you start running big tires and/or higher gears, and/or an OD trans without the freakishly low stock first gear, you lose bottom end gearing...something a stock M715 is blessed with and most factory trucks aren't....a big advantage in a lot of situations....
What are your plans for using the vehicle...what kind of budget.....preferences for chevy/gm/ford/dodge/???
brute4c

[ajbirken]

The best way is to take the cab and bed and put in on a dodge CTD frame and chassis.

Probably the easiest way is:

350/700R4/44inch tires or bigger.

[brute4c]

44 inch tires need a spring over and additional lift or fender carving.....more bucks....
but that might be ok for him.....
brute4c

[oddave]

These trucks just aren't made to run on the highway, plain and simple. If you wanted a four wheel drive Ferrari you could probably build that too but is it practical? I guess its all in how much money you've got burning a hole in your pocket. Dave