K5 with 700r4 question

[DBear]

hey guys, thinking of swapping in a 700r4 into my 72 K5. It is bone stock, with the original 350, TH350 trans, NP205 with 3.73 gears. Going with a 2.5 inch lift and 31.7 inch tires...235/85/16's. Can anyone give me experience or opinions on mpg and performance? Thanks in advance

[DeadheadNM]

I've got trucks here with 33" tires and both 700r4 and th350 transmissions (and 4.10 and 3.73 gears respectively). IMO unless you do a lot of highway driving I'd stick with the th350. I'm building a blazer now and plan to keep the th350 even if I swap the 3.07s to 3.73s.

Not too many K5s with all original drive trains.

[DBear]

Originally Posted by DeadheadNM

I've got trucks here with 33" tires and both 700r4 and th350 transmissions (and 4.10 and 3.73 gears respectively). IMO unless you do a lot of highway driving I'd stick with the th350. I'm building a blazer now and plan to keep the th350 even if I swap the 3.07s to 3.73s.

Not too many K5s with all original drive trains.

I hear that....I really don't wanna mess with this drivetrain since it's original, just thought it would be nice to have the overdrive. I plan on bringing it to NM next summer, Ruidoso area, and do some trailing.

[hemi43]

Putting an overdrive transmission behind an old school engine wont give you the gas mileage you would expect mainly because the older engines are not designed to run efficiently at 1900 RPM. If you want fuel economy, then you will have to upgrade both the engine as well as the transmission. Your 3.73 gears are a bit low for an overdrive application especially with your tire diameter anyway, so you're looking at a big expense for everything to run nicely together.
For comparison sake, I have a 5.3 with a 4L60E and 4:10 gears turning 33" tall tires. I get a true 25 MPG (imp) which is equal to 21 MPG US. Unless you're willing to do a complete package, don't waste your time.IMHO

[ClassicStyle]

I have a 383/700r4

I like the combo, runs nice down the highway at 75mph.

It's getting pulled for a ls2/4l70 at a later date

[mister.freeze]

Originally Posted by ClassicStyle

I have a 383/700r4

I like the combo, runs nice down the highway at 75mph.

It's getting pulled for a ls2/4l70 at a later date

Same combo here. I used to drive a lot highway miles and it worked well. Now I don't, and would like to try a 4l80 trans. On my best day, I get about 10mpg.

[hemi43]

Originally Posted by mister.freeze

Same combo here. I used to drive a lot highway miles and it worked well. Now I don't, and would like to try a 4l80 trans. On my best day, I get about 10mpg.

10 MPG ? Wow, that would kill me up here in Canada. Regular gas right now is $4.04 per US gallon and is going up in the new year.

[twp1]

Hemi 43 what adaptor did you use on your trans to transfer case?

[hemi43]

Originally Posted by twp1

Hemi 43 what adaptor did you use on your trans to transfer case?

I used the Advanced adapter. Worked great.

[4oldcars]

I put a crate 350 in my 2 wd with a 700R4. Pain in the backside, no advantage and cost a ton of money. Wish I'd kept the 350 trans. Cheaper - better.

[Lieferson]

Its all about the smiles per gallon. No one buys a brick on wheels with a V8 for Miles per gallon

[DBear]

agreed....too much for an occasional driver.

[Bigdav160]

No longer have my K5 but I drive it's big brother K20 Suburban.

I like the 4L60 overdrive. Lower first gear for better take off. Overdrive for less stressed engine. Small increase in fuel economy but having the engine last longer has it's benefit. Quieter in the cabin too.

Moving the engine forward isn't a terrible task. Shorten the radiator hoses and lengthen the exhaust pipes.

[Tom Vogel]

I dont like the 700r4. Its shifts like a powerglide with an over drive.