86 1/2 ton gears needed for 33” with new 383

[1986Chevy]

So pulling the trigger on a 383 with the 700 R4 had it rebuilt with corvette servos with 2000 stall converter and transfer case Np208 rebuilt was told the current gears are 273 with running a 4” BDS lift and 33” KO2 what gears and brand would you all recommend? Any advice greatly appreciated

 

[Grit dog]

Guess I’d verify what’s in it first lol. Totally possible it had those originally though.
Like most of these type of questions, it up to you to decide what you want out of the truck. Mud bogger vs pounding it 85mph down the highway frequently beget different gears. Both fir out of the gate and for cruising speeds and your rpm tolerance at speed.

 

[PrairieDrifter]

3.73's at the very least. Probably 4.10's though.

I'd say you'd most likely be okay with 3.73's with a fresh 383.

Like said above, it depends what you're doing with the truck.

 

[1986Chevy]

It came with 273 was thinking 373 or 410s will be using as an almost daily driver and do travel up the mountains from 1500 ft to 8000ft most weekends snow, ice in normal winters haven’t had any this year and mostly desert and mountain 4 wheeling in the summer highway driving to get there so I guess something for four wheeling and highway

 

[PrairieDrifter]

4.10's I would probably go with. But that's just my opinion. You don't want to have to regear twice

 

[bucket]

4:10 minimum. 4.56 ideally. I ran the 700r4/3.73/33" combo for a long time and to be honest, it absolutely sucks.

 

[bucket]

I guess I should elaborate, it absolutely sucked on the interstate. The gearing was too tall, any little incline or the slightest headwind would require enough throttle that the converter would unlock and and then your running down the highway with the converter unlocked all the time which will cook the trans. So often I was just putting it down into third to keep the trans cool and just keeping it there, which defeats the purpose of having an overdrive trans to begin with.

When it comes to pushing a brick through the wind, gearing for "economy" will hurt you more than it helps. GM really f*cked up the gearing options of the 4x4's in the 80's and it was a very poor attempt to gain economy. You don't want to do what they did.

 

[Grit dog]

^Good point. And agree. Underpowered OE engine and OD trans, has no business having gears that start with a 2 or even low 3s.
Also suggest OP run some rpm/gear calculator options to get a visual of what rpm’s will be in upper gears at certain speeds. For reference.

 

[Zelph]

I’d go with 4.56. I like having the grunt to power up steep inclines and maintain a speed. A top speed of 70-75 is just fine by me.

 

[Craig Nedrow]

There are 383's and then there are 383's. Engine internals will dictate where your torque will be rpm wise, and also how much torque overall, anywhere from 300-500. 2.73, 33" tires, 2000 rpm's and .67 OD=about 107 mph. Just changing to 3:73 = 78 mph. 4:10=71 mph. 4:56 = 64mph. Bucket is on the money, 4:56 @ 2800 rpm = 90mph, which is more then acceptable for sb, or bb. Overdrive make all the difference. Friend has a performa built 700r4 behind a 427 sb 650 hp, and has blown it twice on six months. There is a guy in Calif that worked for GM transmission, in his 70's now. He sells a kit that last check was about $1100 hand written instructions. My friend Tom has built a bunch of these. He is in the process of building three more. His son has a procharged 498 I believe, close to 1000hp with one of these modded trans, and it has not broke. Just some info for ya. Make sure when you build the motor, take pics so we can enjoy following along.

 

[PrairieDrifter]

Agreed. I'm off the basis of a worn out 350 and 33's and 35's. Highway is liveable, interstate would not be, not at 80 and 35's anyways. Lifted squares don't belong at 80mph anyways lol.

The first gear is really nice even with 35's on the street and casual off-roading. You'd want to be in low range for any real crawling anyways. That and his usage is why I said 4.10's. Mountains could use 4.56's though, was just dependent on his usage and engine build.