th400 transmissiom

[tthornt]

Hey all, i need some help.

I have 1983 chevy Custom deluxe SWB (Poor gas mileage)
I'm running a chevy sb 283 (Stock) with a th400 tranny, & edelbrock 1400.
I'm thinking the engine is not strong enough for th-400
Any one running the same setup? or am i using the wrong application?
Can some one shed some light and/or point me in the right direction?

Thanking you in advance.

[Warrens69GMC]

Most of these trucks get 10-12mpg.

some questions -
tire size
rear gear ratio
are you talking in city driving or freeway driving
do you have anything in the cab or in the bed?
Your weight (it does factor in)

[tthornt]

tire size 225 70R15
Rear End 308 i'll verify tomorrow when i replace axle seals.
High way mileage is what i'm concern with.
I have a toolbox full of tools. which i'm going to remove.
i replaced the bench with bucket seats and i have a spare tire and medium size floor jack in the bed.

[Zane M]

What is "poor" gas milage? 10-12 is probably the norm, but there are always exceptions.
A TH400 consumes about 50 HP, so yeah, your 283 may not be enough engine, depending on what HP it has, considering the 400 was designed for the 350 CI engines and above.

[tthornt]

I'm getting about 12 miles to the gallon.
A buddy of mine has a 200r tranny. I might buy it. if i can't get better gas mileage out of the present setup

283 SB-Suffix code = F0407GF
1965 283 – 195HP

[Warrens69GMC]

Really the problem is the weight and the powerband of the 283. The stock power of the 283 is near the 2500-3000 (65mph) for the stock cam, higher for a larger (aftermarket) cam. a 200r4 will push this farther away from the powerband, essentionally lugging the motor and could increase gas usage.

When GM put the inline 6's (230,250,292) in the trucks, most of them had higher gears (3.42,3.55,3.73,...) as to put them in the powerband of the engine. Since your cubic inch is near this level, you may need this style of gear ratio.

For the 3.08 gears and TH400, you may need the torque and HP of the 327 or 350 for your needs.

[tthornt]

Interesting! Initially i had a 373 or 411 positive traction rear end. and the truck felt like something was holding it back. i replaced the original rear end with what i was told was 3:08. the truck no longer feel like it's being held back, until i get to about 65MPH. When i replace the axel seals i will count the teeth to be certain. When i reach the power band limitations is when it seems to burn more gas.

so the 200r OD Tranny is not the solution? i guess my solution will be change the rear or live with what i have? Installing another motor is not an option.

Will a th350 yield better gas mileage?
Are there any other solutions?

i built this truck for gas mileage.