Gear ratio for D35/8.8 with 2.9l V6

[KJ]

I'm currently in the middle of swapping the front and rear ends on my 88 and am also thinking about throwing some new gears in as well. I'm thinking in the 4.10 to 4.56 range, but was hoping to get some feedback on how the pickup will drive with these gears. It has the 2.9 v6 and the 31 spline 8.8 with a D35 up front. I'll probably run 33 inch tires and am not looking for a rock crawler or anything like that, just not a high-geared, gutless SOB.

Also, I hear that some people prefer having either higher or lower gears up front vs. in the back (don't remember which is supposed to be lower). Is there any truth to this and what is the advantage of this setup?

Any feedback greatly appreciated. Thanks!

 

[bigmark303]

I would go with 4.56 gears at the least. If 33 inch tires are your goal with the 2.9 be prepared for it to be gutless even with gears. My 4.0L OHVs with 4.56 were still gutless above 55mph with 33x10.5s.

Also the gear ratio front to rear needs to be the same as well as tire size being the same. When in 4wd front and rear is locked together and you cant have them rotating at different speeds because they will bind up and parts will fail rather quickly.

The only time you would see different ratios front to rear would be in say 4x4 tractors with smaller front wheels than the rear. The ration is different between the front and the rear to keep the rotational speeds of the shafts the same while working in 4x4 because of the difference in tire diameter. There really is no need for a pickup truck to have different ratios.

 

[swynx]

if you want pep and a little more gear id go 4.88 with 33s, i think 4.56 would be closer to stock tho.

 

[4x4junkie]

^^

Agreed. 4.88:1 if you're running 33" tires (2.9L).
I run 5.13s w/35" tires (same equivalent) and it's about dead-on perfect, no problems merging/keeping up in traffic, gets decent mileage, etc.

 

[Beef52751]

I would go with 4.56 gears at the least. If 33 inch tires are your goal with the 2.9 be prepared for it to be gutless even with My 4.0L OHVs with 4.56 were still gutless above 55mph with 33x10.5s.

Also the gear ratio front to rear needs to be the same as well as tire size being the same. When in 4wd front and rear is locked together and you cant have them rotating at different speeds because they will bind up and parts will fail rather quickly.

The only time you would see different ratios front to rear would be in say 4x4 tractors with smaller front wheels than the rear. The ration is different between the front and the rear to keep the rotational speeds of the shafts the same while working in 4x4 because of the difference in tire diameter. There really is no need for a pickup truck to have different ratios.

Some do run different gears front to rear, most mud trucks do to keep the front axle "pulling" the truck...that being said all of them are trailered to the bogs, make a few passes and trailered home. So while it is NOT a good idea for the op to run different gears, it is a fact that some trucks do and that may be where he heard that.

With all that being said I have a 2.9 with 4.10s and 33x12.5s and it isnt unbearable but if I didnt have the gears laying around I would've went with a 4.88.

 

[lvwill]

I have a 92 with 2.9 and auto trans. With 31s and 4.10 gears it was a gutless wonder on the street and wouldn't hold overdrive on the highway. Was getting around 14 mpg. Now I have 33s and switched to 4.88 gears and it's a completely different truck, runs great on the highway and getting around 20 or so mpg loaded with all the camping gear.

 

[KJ]

What kind of rpms, speeds, and gears are you guys getting with various gears? Like 65mph in OD running 2500 rpm for example. Also, what advice do you have for purchasing and installing gears? Looks straightforward to install, but a bit technical.

 

[Will]

Those old motors, you want to keep your cruise below 3000rpm. Above that, your engine will stop reading the O2 sensor and be in open-loop, which means the computer will be fueling in a way that makes sure the motor doesn't go into a lean condition and burn the edges off of the exhaust valves.

But that is fine with these motors. What you want to do is arrange the gearing so that the motor is spinning near its torque peak at your cruise speed. The point of max torque is also the point where the engine is most efficient in these engines. That is 2600rpm with a 2.9 and 2400rpm with a 4.0. Gear the truck to hit those revs at your desired cruise speeds.