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What Better Gear Ratios For TH400 To Get To Just 70MPH In A 1983 C20 4 Door Dually 454 Carburated

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blackandgold51

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I got a 4:10 ratio. Which when I get up to 55mph on the highway the engine screams and screams high past 60. After that gets "dragged" past 60mph

I want to get to 70mph and that's it. Nothing father than that

I would do a 4L80E Transmission but that's costly and I hear those transmissions fail along with having to deal with the computers,while the Turbo 400 remains sturdy and I can tow heavy.

I don't go up to 100mph because I don't drive fast, plus I want it to still be streetable also in the 35 to 40 mph speed zones. Also, I'm not looking to drag race neither, especially since I'm easy/light on the throttle.

454 also has Longtube headers
 
4l80 fail?? Yes everything can fail but never heard of one very often. If you lower gear ratio then you loose pulling power. I’d say a good compromise would be 3.55.
 
Just throw on bigger tires.

Since it's 2WD have you looked at add-on overdrives?
 
4L80s are quite reliable. My 91 454 has 150k, my 99 6.5 has 139k and my wife's burb has 220K all with only fluid changes so far. One might be able to point to the two shift solenoids that can go bad, but even those are not too frequent.

Swapping to 3.73s would give you a similar result to an 80e while in OD. Without knowing your tire size, towing etc hard to further help.
 
bigblock454 said:
4L80s are quite reliable. My 91 454 has 150k, my 99 6.5 has 139k and my wife's burb has 220K all with only fluid changes so far. One might be able to point to the two shift solenoids that can go bad, but even those are not too frequent.

Swapping to 3.73s would give you a similar result to an 80e while in OD. Without knowing your tire size, towing etc hard to further help.
Click to expand...
Wheel size is 16 while tires are 33s
 
https://ck5.com/forums/threads/us-gear-vs-gear-vender-overdrive-units.327497/

Gearvendors: https://www.drivetrain.com/gm-3-sp-automatic-05-gm-3-sp-automatic-3dfs400a

You can see that the aftermarket O/D isn't cheap. While the Ranger is cheaper, I think they only make them for manual transmissions.

Regular 33's are about 32" inches tall, which makes 60MPH = 2750RPM and 70MPH=3175RPM. If you're OK with the 2750RPM, but want that at 70MPH, that's 3.55 gears as mentioned above, or a swap to some 37" tires, but the acceleration will suffer either way. Maybe that's OK with the BBC - only you can decide what you want from the truck. Of course having 4 speeds makes it a better performer and more versatile. (Hence why automatics have progressed from 2-speed, to 3, to 4, 5 and now 6-speed and more)
 
Blue85 said:
https://ck5.com/forums/threads/us-gear-vs-gear-vender-overdrive-units.327497/

Gearvendors: https://www.drivetrain.com/gm-3-sp-automatic-05-gm-3-sp-automatic-3dfs400a

You can see that the aftermarket O/D isn't cheap. While the Ranger is cheaper, I think they only make them for manual transmissions.

Regular 33's are about 32" inches tall, which makes 60MPH = 2750RPM and 70MPH=3175RPM. If you're OK with the 2750RPM, but want that at 70MPH, that's 3.55 gears as mentioned above, or a swap to some 37" tires, but the acceleration will suffer either way. Maybe that's OK with the BBC - only you can decide what you want from the truck. Of course having 4 speeds makes it a better performer and more versatile. (Hence why automatics have progressed from 2-speed, to 3, to 4, 5 and now 6-speed and more)
Click to expand...

Who and what someone was thinking? When they made 3 speeds only Transmissions still in the late 1970s early 1980s .

Besides the 700R4

And it's suprising some of how large tires can make a difference
 
Blue85 said:
https://ck5.com/forums/threads/us-gear-vs-gear-vender-overdrive-units.327497/

Gearvendors: https://www.drivetrain.com/gm-3-sp-automatic-05-gm-3-sp-automatic-3dfs400a

You can see that the aftermarket O/D isn't cheap. While the Ranger is cheaper, I think they only make them for manual transmissions.

Regular 33's are about 32" inches tall, which makes 60MPH = 2750RPM and 70MPH=3175RPM. If you're OK with the 2750RPM, but want that at 70MPH, that's 3.55 gears as mentioned above, or a swap to some 37" tires, but the acceleration will suffer either way. Maybe that's OK with the BBC - only you can decide what you want from the truck. Of course having 4 speeds makes it a better performer and more versatile. (Hence why automatics have progressed from 2-speed, to 3, to 4, 5 and now 6-speed and more)
Click to expand...
Blue85 said:
https://ck5.com/forums/threads/us-gear-vs-gear-vender-overdrive-units.327497/

Gearvendors: https://www.drivetrain.com/gm-3-sp-automatic-05-gm-3-sp-automatic-3dfs400a

You can see that the aftermarket O/D isn't cheap. While the Ranger is cheaper, I think they only make them for manual transmissions.

Regular 33's are about 32" inches tall, which makes 60MPH = 2750RPM and 70MPH=3175RPM. If you're OK with the 2750RPM, but want that at 70MPH, that's 3.55 gears as mentioned above, or a swap to some 37" tires, but the acceleration will suffer either way. Maybe that's OK with the BBC - only you can decide what you want from the truck. Of course having 4 speeds makes it a better performer and more versatile. (Hence why automatics have progressed from 2-speed, to 3, to 4, 5 and now 6-speed and more)
Click to expand...
I forgot to mention that I also a stall torque convertor
 
Your going to want OD ideally. Those trucks were geared for the 55mph speed limit back then. Otherwise Id get 3.42s and run it with the th400.
 
blackandgold51 said:
LT245/75R16s
Click to expand...
:eek1:

Get an NP205 transfer case and install it backwards. 3300RPM becomes 1650RPM :thumb:. Good luck shifting it at highway speeds!

But seriously, the 4L80E will bring your 3300 down to 2475. It will actually seem better than 0.75 because you'll have lockup.
 
and just a fyi for you . . . the 4L80-e shares a LOT of hard parts with a th400 . so you saying there weak is kind of funny . there a much stronger unit than the 700r4/4L60-e units for big trucks tho .

and look at these guys for a nice controller unit . www.usshift.com
 
+1 on the 4L80E. You get overdrive and a lock up, plus they will put up with a lot of abuse.
 
acm said:
+1 on the 4L80E. You get overdrive and a lock up, plus they will put up with a lot of abuse.
Click to expand...
and in gm factory use they were installed behind duramax engines in the G-series vans if you can find one . there is not a lot of them out there but they are out there . i have seen 2 and worked on 1 .
 
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