Rear End Gearing

[The Lost Texan]

1985 SWB with a LS3 6.2 and 4L70. Ordered a 9” rear end from Quick Performance. Does anyone have suggestions on the final gear for cruising, in town driving and road tripping on the interstate. I will not be drag racing or auto crossing. Just cruising 50-70 mph. I understand tire size is a factor, however, I didn’t know what these particular engines like for RPM’s. I was leaning towards 3.50, maybe 3.73. Anyone have opinions or feedback? Thanks.

 

[Keith Seymore]

Yep. 3.70 will be a nice overall ratio with an OD trans.

K

 

[Keith Seymore]

Hopefully you are not in a big hurry.

I ordered mine back in November and the parts are just now starting to trickle in.

(I'm not in a big hurry).

K

 

[TotalyHucked]

LS engines make peak torque higher in the rev range (usually around 4k or so), so don't fear a gear. I've got a ~425hp 5.3 and it used to have a 4L65 behind it with a 3000 stall converter (got a T56 now) and I went with 3.90s when I did the 10-bolt. That was the PERFECT combo IMO. Cruising at 70 I was right at 2250 with a 28" tire. Still nice and relaxed, exhaust wasn't singing but it would stay in OD/lockup even up hills. But then especially with the stall, it would get rowdy when you wanted to lay down on it. Perfect middle ground IMO. I put 27.5k miles on that setup and never once regretted the gear or wanted more.

3.55 or 3.70 would give you a nice comfortable sub-2k cruise RPM but it may come out of lockup more than you'd like. I personally would never go taller than 3.73. 3.90 or 4.10 would get my vote

 

[The Lost Texan]

Thanks Huck. I was thinking a 28" tire, as well. I will have to reevaluate.

 

[TotalyHucked]

More specifically, that's with a 315/35/20. With my T56 having taller gearing, I'll be swapping to 4.10s or 4.30s soon