turbo 400 to 700r4 swap......should i do it?

[80goldenburb]

^^^ a 400 is only superior in strength. 4L80 toggle swtich shift with vac modulator is the best option.

 

[smoothandlow84]

I have a built 700r4 mated to my 350 small block in my square and I dont have any complaints, especially on the highway...85 mph and 1900 rpm in o.d. It sips fuel when cruising in o.d., and when I mash the pedal it breaks the tires loose. My transmission guru installed corvette goodies into it with the full rebuild including a new torque converter. I am glad I ditched the turbo 350 and had the 700 installed. The 700 is from an 88' and so is the 350 small block.

 

[rpcraft]

Just throwing this out there, but with a little work, engenuity, and some education on the matter you could upgrade to a stock 4l80E, use a later model PCM out of a 2000 and GM truck,, and then all you have to do is provide the inputs needed by the PCM to act as a trans controller, with a little work from a tuner. I think the only catch 22 is you technically would have to get a VSS fed speedo, or some type of digital to analog to see your speed, or you can replace the speedo with a aftermarket GPS unit (or say screw it and use your phone with a speed app). It is kind of the best of both worlds. Dependability that the th400 had, plus OD for the highway and it does have the taller th400 first gear.



This site below discusses the setup and stuff
https://sites.google.com/site/sloppywiki/everything-ls/cheap-stand-alone-trans-controller

 

[80goldenburb]

With any over drive transmission you need to gear down. You can't lug your truck on the highway expecting to see fuel savings.

The 700 is not a cheap transmission to rebuild let alone beef up. Not like a TH400 that's for sure.

You would like the lower 1st gear the 700 offers!

Thats only a half correct answer. Sure if you have the 10 or 12 bolt and 2.73 - 3.08 gears then yes. BUT, if, like my truck that has the 14 bolt full floater with the tallest possible (and rare) 3.21 gear, than you can keep it. I swapped a 700r4 behind my 502 and kept the 3.21s out back while gaining 6 mpg FREEWAY driving. City stop-n-go stayed the same. When I swapped out the 700 for a manual 4L80, mpg stayed the same, but had to go bigger tires (31' to 33') to keep the same rpms as the 700r4, since the 80 has 25% OD vs the 700's 30%. i like running 2K rpm at 70 vs at 60 mph