E Rod and a 4L65E

[GMJimmy]

I'm planning on putting a connect and cruise setup (LS3 with a 4L65e) in my 70 shortbox stepside and I'm looking for some suggestions for the right rear gear ratio to use. The truck with 29.6" tires has a 3.08 in it now which will rev at 1704 rpm at 70 mph. 3.73's will rev at 2085 so I'm thinking maybe 3.55's may be better at 1964 rpm. Is anybody using the 4L65 or anything with a .70 (.696) OD and similar rear gear ratio that can tell me how they like it?
Suggestions appreciated.
Jim

[SactoJim]

I think the general consensus is 3.73's are the best choice for auto 4 speed overdrives. 700R4 in mine with 3.73's.....works great!

[71meangreenc10]

3.42 for all my 700R4's.

Good take off and great on the highway.

Smitty

[GMJimmy]

Thanks for the replies. 3.42's will get me to 1892 rpm at 70. What size tires are you guys running?

[donandal]

I have that erod /4l65E in my truck...just got it in December.

the documentation with it recommended 3:42 with about a 29 inch
tall tire as I recall

[68c10airstream]

I just finished going to 18" wheels and a 28.2 diameter tire from a 26.5 diameter running through the same 3.08 ratio with a 5.3/4l65e and suspected a reduction in low end take off, and was correct. Rear end change/ratio change in the future and will be going to at least 3.50 or higher.

[GMJimmy]

Thanks for the replies! I think I'll check out the GM documentation before I decide. I had a 2010 Corvette with a 26.7 tire and a 3.42 rear gear and in 6th with a .50 OD I was revving about 1509 rpm. A little sluggish but 6th was a fuel economy gear. 30 mpg with the LS3. I wonder if rpm that low would work in my C10?

[69 GMC Daily Driver]

Originally Posted by GMJimmy

I'm planning on putting a connect and cruise setup (LS3 with a 4L65e) in my 70 shortbox stepside and I'm looking for some suggestions for the right rear gear ratio to use.
Suggestions appreciated.
Jim

^
Jim,

My LS6 and 4L65E are running 3.73 (w/posi.) It absolutely runs like a champ.
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[Heavymetl]

I've got a 3.25 9" with a 4L80E.

Granted, I just got the truck driving yesterday, but the 3.25 seems too tall for anything other than highway driving. I don't think you'd be dissapointed with 3.73's.

[CarterD2015]

Depends on the type of driving that you are most likely going to be doing. I chose 3.73s because I drive mostly in town and I'm not going to be doing much highway driving.

[GMJimmy]

I'm planning on both highway and city. Around town and those long road trips to the Goodguy's shows. I have a 2006 Silverado with 3.73's and a 6.0 Vortec Max and a 4L65E and it runs about 2000 rpm at 70 and has a 30" tire. The C10 is a lot lighter so I should be ok with something like 3.55 to 3.73. Thanks everybody for you suggestions! Really helps the decision.
Jim

[HSRACER]

I have both a 3.73 and a 3.42 ratio rear end with the overdrive trans. I like the 3.73 but the 3.42 is the perfect combination of acceleration and mileage. If building from scratch I would always do the 3.42 ratio.