3.08 or 3.31 with 4L65?

[CaliWagon83]

So, it’s going to be quite a ways out until I ultimately have to make this decision, but I’m trying to narrow down my choices on a rear-end ratio once I do the E-Rod swap. I know the Ford 9-inch is popular, but I’m leaning toward the 12-bolt. I’ve kind of narrowed it down to 3.08 or 3.31.

To be clear, I’m not aiming to build a drag strip demon or the fastest G-Body wagon out there. I just want a fast, reasonably fuel-efficient cruiser that I can drive around town and maybe the occasional road trip.

I know a 3.73 would really wake it up around town, but I don’t want it to be too frantic on the highway. I typically cruise between 70-80 on the highway, so I want a gear that’ll get me out of the “drone zone” which seems to be between 1,500-2,000 RPM.

Seems either the 3.08 or 3.31 would bring it above 2,000 at between 75-80. This should also be kind of the sweet spot for fuel economy. I would be thrilled to get about 22-23 highway.

Any thoughts, personal experiences, or advice appreciated. Thanks.

 

[Longroof79]

I'm thinking between a 3.23 to 3.42 gears should keep you within that "sweet spot". Also, depending on what cam you're using could make a difference in the way the car cruises.

 

[CaliWagon83]

It’s just going to be an out-of-the-box stock-spec LS3. The LS’ are a tad peaky in my experience compared to traditional SBCs, but the upside is they have a lot more power higher in the rev range. With 376 cubes, I’m thinking low-end torque shouldn’t be too much of an issue with 3,500-3,700 lbs (est.)

 

[TURNA]

4:22's

 

[CaliWagon83]

4:22's

Sounds like you live your life “One 1/4 mile at a time.”

 

[pontiacgp]

Your 4th gear is close to my 5th and I have a 3.08 rear, at 75 mph I'm at 1900 rpm.

 

[Wraith]

Drone is dependent more on muffler/exhaust choice, whole other question/solution/conundrum. I say why bother taking advantage of overdrive with a gear that is fine with a 3 speed transmission?

What is your "around town" vs "highway" driving mix? Gear to that and you will be much happier in the long run.

 

[CaliWagon83]

Wraith, so you're recommending an even taller rear-end? It has a 2.73 currently, but mated to a TH250 3-speed. It doesn’t currently have a tach, so I have no idea what revs it’s turning on the highway, but when it was still running/driving, I remember it sounding pretty busy at around 70/75. Gearing in the TH250 is taller in the lower gears, and shorter in the higher gears (it’s only a 3-speed, though.)

But the LS3 and the 231 2-bbl are entirely different galaxies power-wise, so I want to make sure I’m making my decision based on the future, not current powertrain.

 

[pontiacgp]

Wraith, so you're recommending an even taller rear-end? It has a 2.73 currently, but mated to a TH250 3-speed. It doesn’t currently have a tach, so I have no idea what revs it’s turning on the highway, but when it was still running/driving, I remember it sounding pretty busy at around 70/75. Gearing in the TH250 is taller in the lower gears, and shorter in the higher gears (it’s only a 3-speed, though.)

But the LS3 and the 231 2-bbl are entirely different galaxies power-wise, so I want to make sure I’m making my decision based on the future, not current powertrain.

this will tell you what your current revs are

http://www.businesspath.com/business_paths/auto/rpm-calc.html

 

[CaliWagon83]

This is the tool I’ve been referencing:
https://www.hgmelectronics.com/gear-ratio-calculator/

Works great on desktop. Unfortunately on mobile, it has an obnoxious newsletter sign-up that I can’t seem to get rid of. That’s helped me to narrow it down to 3.08 and 3.31. OD of 245/45-17s (size I’m probably going with) is about 26”.