400 sbc. . T-400 or 700r4 - Hot Rod Forum : Hotrodders Bulletin Board
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Old 07-26-2012, 09:48 PM
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400 sbc. . T-400 or 700r4

Just like the title says I have a 400 sbc tht "might" have 2 b used as a daily driver 2 work.
Which trans gets better mpg if the round trip of the work trip was around 34 miles a day.
I'm pretty sure the gears in my car are 2.73 so if anyone can throw a better # out there and a good reason why then go 4 it.

I always hear about the 700r4 and its overdrive. So tht peeks my interest because the trip 2 work is 97% highway. But occasionally on a Friday sat or Sunday nite a trip 2 the track.

Can anyone tell me the mpg they get with there th400's or 700r4's

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Old 07-27-2012, 02:39 AM
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Personally speaking...I just converted my 88 chevy crew cab dually from a th400 to a 700r4. my truck is a 2wd with a tbi 350. I went from around 8mpg to 15 on the highway at 60mph. before my truck was screaming at 60, mostly cuz i have 4.10 gears. but i do pull on occasion and the 700r4 appealed to me because it has a deeper 1st gear. beware though, if your putting in a stock version it will be kind of week by todays standards, and if your car isnt equipt with the wiring you will have to wire in a lock up switch for the converter. If you have the recources have a reputable transmission guy build it, then he can do a hydraulic lockup with no wires, and some good internals with vette servos. then you can race it and drive it.
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Old 08-05-2012, 05:32 AM
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You don't state what size rear tire you are running but i doesn't really matter with the 2.73 gear. You will drop your rpm range too low to be useable on the highway in overdrive with the 700r4 with that low of a numerical gear.

I believe the lowest gear I would want is a 3.42 if I were running an overdrive with your setup, though going bigger numerically(say 3.70, 3.73, 3.90) will help get it rolling and still keep you in a useable rpm range while cruising on the highway with the over drive.
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400 th400 700r4

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