Powertrain question

[Green 1959]

I have a question on the powertrain. I have a 1/2 ton with 4.11 rear and set up for a turbo 350. There is a place locally that can convert to 3.38 ratio, I was thinking about maybe using a 700r4 trans, is this setup going to be overkill for something that I want to daily drive and that is freeway friendly? Im hoping to get the best fuel mileage possible with a 250 l6

[72Mountaineer]

In my experiences, the lowest gear (numerically) in the rearend that you can use with an overdrive tranny, be it a 700R4 or a 2004R (which is my recommendation) is a 3.42. Anything lower will need a much higher stall converter just to get you away from a stoplight, especially with tall tires.

[tmoble]

3.38 ~= 3.42 that'll be fine. With a 250 L6 it may a little short of power in OD, have to drop into 3rd on hills, etc

[dicer]

A 700R4 won't fit unless the rear crossmember is cut out.

[tmoble]

if it already has a TH350 the TH700 should fit. google will have a million results on converting from 350 to 700. driveshaft length is different among other things.

[blackdiesel]

you will have to move the crossmember around 2" back, and need a little more clearance (around 1") at the hump, but should be know problem. Grandpa has 2:73's with a 700r4 but has a 350 in his 57 belair and it does ok. If your in flat country you should be fine, 3:73's would be my pick with the 6 banger though.

[tmoble]

I think blackdiesel is right. You'll probably be needing the extra gear with the 250. I have a torque monster 406 with 200-R4 and 3.73 in my Chevelle. I don't need the extra gear and have been trying to find somebody with a 3.36 or so to swap gears with. The 700 has a little less OD ratio, get more RPM with the same gears.

[Green 1959]

I have a combo that I'm going to try: '78 250 inline, a 700r4 and 3.38 rear end. I want to see how it works, will be awhile before I will have it all ready, tires are going to probably be 235/75/r16. I'll let you know how it works out

[JumboAMONGus]

just keep the 4.11s ,you got overdrive now

[Green 1959]

I might keep the 4.11 rear end around, but I'm wanting be be able to go on long trips with my truck and use it as a daily driver, that's why I'm not working too hard on the body work. You know the jerks at grocery stores Also Jumboamongus your truck rocks, I didn't see a build page for it though. Would like to see more picts.

[JumboAMONGus]

i willmake one here shortly ,i just got the photobucketand found my old pics

[azsnow]

Originally Posted by blackdiesel

you will have to move the crossmember around 2" back, and need a little more clearance (around 1") at the hump, but should be know problem. Grandpa has 2:73's with a 700r4 but has a 350 in his 57 belair and it does ok. If your in flat country you should be fine, 3:73's would be my pick with the 6 banger though.

I have a mild 350 with a 700R4, and the flat panel fits perfectly, no added room needed.